The gobies, family Gobiidae, are among the most speciose fish families, with more than 2000 species in 200 genera worldwide and a long taxonomic history (Van Tassell 1998). They are generally small- to mid-size fish that dwell mostly in shallow warm marine waters, although some inhabit brackish waters and estuaries and a few hundred species live in fresh water environments. Gobies have fused pelvic fins that they can use as a suction device to hold rocks and other objects in their environment. This sucker is functionally analogous (of separate evolutionary origin so not homologous) to suction-forming organs in in other fish, for example remoras and lump suckers. Most goby species eat small invertebrates and plankton, some eat other fish. Gobies are important prey for many larger fish. Few goby species are fished commercially as a human food source; some examples are: round goby, monkey goby, toad goby, and grass goby. Some species of salt-water gobies are popular in the aquarium trade.
(Van Tassell 1998; Wikipedia 2012)
Currently 212 genera and 1,875 species are recognized, making gobies the largest marine fish family and the most species-rich family of vertebrates. Gobies and blennies combined make up a dominant portion of the small fish inhabiting benthic tropical reefs around the world. Additionally, gobies are usually the most abundant freshwater fish on oceanic islands. This group is so poorly known due to their cryptic and secretive nature that 10 to 20 new species are described each year, making them the marine family with the greatest number of newly described species. The range of morphology, behavior, habitat and reproductive strategies within this family is undeniably impressive.
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Group 4: longfin gobies .
Psilotris, Varicus, Chriolepis, Pycnomma, Gobulus, (and Robinsichthys)
Although gobies are known for having fused pelvic fins, often in the shape of a sucking disk, several goby genera have divided pelvic fins to various degrees. The division can be partial or full, although the bases of the split pelvic fins are usually in contact. This character is shared by the related gobioids of the families Eleotridae and the similar appearing (but not gobioids) Ptereleotridae, which have pelvic fins that are separate, even at the base.
In some gobies, the divided pelvic fins are clearly acquired after the larval phase. For example, Coryphopterus personatus larvae have fused pelvic fins despite the fact that juveniles and adults have separated pelvic fins. A closeup photograph of the pelvic fin of a 7.6 mm SL larval C. personatus at right clearly shows the connecting membrane. Series of transforming larvae show variable states of fusion of the pelvic fins. It should be noted, however, that the majority of larvae in the collections have frayed fins and the state of fusion cannot be evaluated. This is especially the case for the difficult genus Coryphopterus, where the pelvic-fin morphology is, unfortunately, an important species-level character.
Other larval gobies, such as Gobulus myersi and Psilotris amblyrhynchus, can have partially-fused pelvic fins. G. myersi is an interesting contrast to larval C. personatus in that it shows the opposite sequence of pelvic fin morphological changes: it starts as a partially-divided fin in larvae (left) and subsequently fuses in adults.
The only six-dorsal-spined species with divided pelvic fins are a sub-group of Coryphopterus (C. alloides, C. lipernes, C. personatus, and C. hyalinus). It is likely that the pelvic fins of all of these species are not divided in pre-transitional larvae.
The seven-dorsal-spined group with divided pelvic fins is quite heterogeneous (with some rare and obscure deep-water taxa), comprising Psilotris, Varicus, Chriolepis, and the individual species Pycnomma roosevelti and very deep Robinsichthys arrowsmithensis.
Three Caribbean goby species have partially-divided pelvic fins (all seven-dorsal-spined): Gobulus myersi, Psilotris amblyrhynchus, and Gobiosoma grosvenori. The latter is a member of the large genus Gobiosoma with otherwise fused pelvic fins and thus it is unclear whether the larvae should be expected to show any division in the pelvic fins. Gobulus myersi adults have fused pelvic fins without a frenum, but larvae clearly fitting this species have partially-divided pelvic fins (D-VII,11-12 A-10-11). Two of the three other Gobulus species have partially-divided pelvic fins as adults (all in the eastern Pacific), and thus the fused pelvic fin in adult G. myersi may be a derived character. In contrast, adult Psilotris have divided pelvic fins and the presence of partially-fused pelvic fins in larvae of Psilotris amblyrhynchus may indicate that divided pelvic fins are a derived character in that genus.
In the genus Psilotris, P. batrachodes has the fewest fin rays with modal D-9 A-7 Pect 16; P. alepis has D-9-10-11 A-8-9 Pect 15, P. celsa (originally "Psilotris celsus") has D-9-11 A-9-10-11 Pect 16-17-19, P. boehlkei has D-10-11 A-10 Pect 16-18, and P. kaufmani has D-11 A-10-11 Pect 16-18-19. P. amblyrhynchus has D-11-12 A-10-11 Pect 17-19. Psilotris are scaleless.
Pycnomma roosevelti has a similar general appearance and a modal fin-ray count of D-10 A-9 Pect 16 (and later develops scales). (Gobiosoma grosvenori also has modal D-10 A-9 (and Pect 17) but is from a fused-fin genus and has only partially-divided pelvic fins and a small pelvic frenum and a very different body shape.)
Chriolepis and Varicus are rare, obscure, and mostly deep-water gobies that typically have divided and long pelvic fins and large eyes. The species comprise Chriolepis fisheri (the only relatively shallow water species (can be found in sand tilefish mounds); D-11-12 A-10-11 Pect 17-18, with two large spiny basicaudal scales), Chriolepis benthonis (over 150m, Gulf of Mexico, D-9 A-8 Pect 16), Chriolepis bilix (described in 2013, over 60m, widespread, D-12 A-11-12 Pect 19-20), and Chriolepis vespa (deep, Gulf of Mexico, D-10 A-7-9 Pect 15-17). The related genus Varicus differs by having unbranched pelvic-fin rays and comprises Varicus bucca (very deep-water, D-9-10 A-8 Pect 16-19), Varicus marilynae (deep-water, Florida, D-9 A-8 Pect 16-18), and V. imswe (deep-water, Belize, with pelvic fins extending beyond the anal-fin origin and D-8 A-8 Pect 14-15). A profoundly deep-water goby, Robinsichthys arrowsmithensis, has D-VII,11 A-11 and is distinctive with 22-23 pectoral-fin rays.
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Group 5: divided pelvic fin gobies .
Evermannichthys, Evorthodus, Ctenogobius, Gnatholepis, Nes, Bollmannia, Gobionellus, Gobioides, Microgobius, and Palatogobius
Gobies with 12 or more dorsal and anal-fin rays have a generally different look from the short-fin gobies; they are more likely to have a long tapering body and a relatively short caudal peduncle. Although uncommonly encountered by divers, these gobies are abundant on sand and silt bottoms near reefs and in brackish waters along the coast. One species, the Goldspot Goby Gnatholepis thompsoni, is commonly seen on the reef. The long-fin gobies mostly comprise those species that live on soft substrates, often in holes, and sometimes with symbiotic shrimp partners. The high number of fin rays and long narrow bodies are likely adaptations to hole-dwelling. Their larvae are typically lightly marked and relatively small, thin, and long. Those species with characteristically blunt heads and subterminal mouths have larvae with pointed snouts and terminal mouths which undergo marked head-shape changes at transition.
The larval eleotrid Dormitator maculatus has a similar general appearance and shares most of the markings, including the abdominal promontory and jaw angle melanophores, but the abdominal midline streak extends to the level of the swimbladder (shared with the other eleotrid species) and there is no internal melanophore around the gut near the vent. Some immature larvae of the long gobies, such as Microgobius superficially resemble this type, but have many more median-fin rays and very short caudal peduncles and are usually longer than 8 mm SL. Immature Bollmannia boqueronensis larvae may resemble this type, but have more median-fin rays and a much larger irregular eye, along with additional melanophores.
Description: Body relatively thick, long, and narrow with a medium round eye and a terminal large wide mouth. Head broad and slightly flattened. Dorsal and anal-fin bases short, caudal peduncle relatively wide and long and procurrent caudal-fin rays 8-9 (8 spindly). Lightly marked, mostly along the ventral midline: at the isthmus, along the pelvic-fin insertion and extending onto the abdominal midline, often with a clear Y-shape diverging from the pelvic-fin insertion (post-pelvic Y), then often a melanophore on the abdominal promontory just forward of the vent, followed by paired melanophores along the anal-fin base and then a row (or streak) extending along the caudal peduncle ending near the start of the procurrent caudal-fin rays. Melanophores are present on the base of most of the lower caudal-fin segmented rays. Melanophores on the head are limited to the angle of the jaw. There are internal melanophores along the dorsal surface of the swim bladder and around the gut near the vent.
Goby 1125 larva
Goby 1125 larvae
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Group 5: divided pelvic-fin gobies .
Barbulifer, Risor, Ginsburgellus, Gobiosoma, Elacatinus, and Tigrigobius
This group includes many of the small gobies on and around Caribbean reefs that live well-hidden around coral structure or inside sponges. Most are inconspicuous and rarely noticed on the reef. The main exception is the group of cleaner gobies that live on prominent coral heads and sponges and remove parasites from passing fishes. They need to advertise and typically have bright blue or yellow stripes on a black background. Interestingly, a set of related sponge gobies share the colored stripe, but do not apparently clean other fishes; the reason for their colors could either be to receive some protection from the relative immunity of cleaners from predation (mimicry) or advertise the fact that they produce noxious chemicals. The striped sponge gobies usually stay in their sponges and do not perch in conspicuous locations as do the cleaners. A group of small non-descript inshore, sometimes even freshwater, gobies are also in this group. The phylogenetic relationships are not resolved and some species have been shuttled around into various genera over the years. The most recent change has been the returning of the non-cleaner/sponge gobies of Elacatinus back to Tigrigobius, where they form a cohesive grouping.
The larvae of Group 3 gobies are typically very small and lightly marked, usually with only a few ventral midline melanophores or often just a single post-anal-fin spot. The basic shortfin meristics (usually 8-11 second-dorsal and anal-fin elements) and general appearance are shared by some larvae of the six-spined standard gobies of Group 2 and the two groups can be a challenge to separate when the dorsal-fin spines are not easily apparent. Similarly, some of the divided pelvic-fin gobies, Group 5, have larvae that are similar in size, shape, and markings to the Group 3 gobies and they also can be difficult to distinguish when the state of the pelvic fins is not obvious. The few Group 3 gobies with 13 second dorsal-fin elements overlap the lower range of fin counts of the longfin gobies of Group 4, but have a quite different body shape and larval appearance. Only the occasional Gobiosoma from US waters have counts that high, but they notably have no more than 11 anal-fin elements.
Most of the Coryphopterus species are sand gobies, i.e. small sand-perching gobies with pale bodies and a set of dark stripes and spots. There are numerous species and larvae cannot confidently be identified to the species level without DNA sequencing. Fin-ray counts can distinguish the sand goby species with fewer or more than 10 dorsal and anal-fin elements, but many of the species and the vast majority of specimens share the 10/10 fin-ray count. The non-sand species comprise C. lipernes, a colorful coral-dwelling species, and C. personatus and C. hyalinus, both colorful hovering gobies that school in groups over corals and sponges. The sand and non-sand species are similar as larvae and share a suite of larval characters, but can be distinguished.
Description: Body relatively thin, long and narrow with a large eye and a terminal mouth. Paired fins medium to long at transition, dorsal and anal-fin bases relatively short, caudal peduncle long and narrow, procurrent caudal-fin rays 7-10 (7-8 spindly). Lightly marked mostly along the lower body: melanophores on the ventral midline at the isthmus and the pelvic-fin insertion (usually streaks). Rare variants have a melanophore on the abdominal midline promontory just forward of the vent. There is a row of melanophores along the anal-fin base, usually five, paired and one per side between the third and eighth element (often merged into a streak on each side). Then, after a space, there is a row of midline melanophores, usually seven or eight unpaired (but often merged into a streak) extending along the ventral caudal peduncle ending near the start of the procurrent caudal-fin rays. Melanophores are typically present on the base of several (usually 4 or 5) of the lower segmented caudal-fin rays extending up to halfway out along the rays. The majority of larvae have one (often none or two, occasionally three or four) melanophores on the dorsal midline just after the last dorsal-fin ray (proportions vary greatly between collections). Some have an additional small melanophore off-center of the dorsal midline near the base of some of the mid-soft-dorsal-fin rays. Many (all?) have melanophores on the distal membranes between the anal-fin rays, usually between the second and sixth elements. Internal melanophores are present at the base of the saccule and often above the saccule and sometimes several around the rear braincase, along the dorsal surface of the swim bladder, and around the gut near the vent. Most individuals have a melanophore at the angle of the jaw, however less-developed larvae are often missing them (but they do have caudal-fin melanophores, separating them from C. personatus).
Early-stage larvae before the completion of all of the fin elements have a dorsal and ventral indentation in the iris, with some later-stage larvae retaining a dorsal indentation in the iris. Series of transitional larvae show development of the eye from a moderately-narrowed vertical oval, often somewhat squared-off, with a small posterior-inferior extension of the iris, to round. The extension has no surface melanophores overlying it, or, at most, a single small melanophore at the dorsal edge (vs. C. personatus, see comparative photograph under C. personatus). Rare individuals show abnormal enlargements of this extension (interestingly, often several in the same collection). There is often a prominently speckled "eyebrow" membrane over the upper half and posterior of the eyeball that appears detached from the pigmented iris below.
Although the length of the pelvic rays are an important character as adults, larvae and juveniles typically have the innermost pelvic-fin ray slightly shorter or about equal in length to the next ray. The pelvic frenum is not usually visible, but may develop on all juveniles in the group (see C. dicrus). Larvae have fused pelvic fins, and the species with divided pelvic fins likely develop the division after transition (unknown for C. alloides, but confirmed for C. lipernes and C. personatus).
The large goby genus Coryphopterus contains numerous species in the Caribbean, several of which are particularly difficult to distinguish, sometimes even as adults. The results of my barcode (mtDNA) sequencing for this group show that many of the important characters used to separate adults do not apply to larvae or juveniles. Since the basic markings and morphology of the early stages are shared by many of the species in the group, DNA sequencing is likely the only reliable way to distinguish species for most larvae and some juveniles.
One of the primary causes of the difficulty in identifying juveniles and adults of Coryphopterus species in the western Atlantic is the extreme variability in the degree of dark markings with habitat. All of the sand gobies have lightly-marked forms on white sand in clear water and heavily-marked forms on darker sediments in more turbid waters, particularly along continental coastlines. This variation can become extreme in several species (C. tortugae, C. bol, C. eidolon, and C. thrix), with some individuals showing almost no dark markings at all. These super-pallid individuals can be impossible to identify to species without DNA sequencing. On the other hand, heavily-marked populations of some typically pallid species, for example C. eidolon, have not been recognized as conspecific and are typically assigned to other species in museum collections.
An additional problem when using the literature and field-guides for identifications is the presence of heretofore cryptic species in the common 10/10 sand-perching bridled-goby group, i.e. the recently twice-redescribed "pallid" bridled goby C. tortugae and a new more-offshore species C. bol (Victor 2008). These species are presently lumped by most observers as variants of the bridled goby C. glaucofraenum. To avoid confusion, I propose that C. glaucofraenum retain the original "bridled goby" common name, while C. tortugae should be called the "patch-reef goby" and C. bol should be called the "sand-canyon goby", after their distinctive habitats.
Most of the characters traditionally used to separate sand gobies do not apply to juvenile or larval stages. For example, the morphology of the pelvic fin is one of the more important taxonomic characters separating the regional Coryphopterus species. The degree of joining of the pelvic fins, the relative length of the innermost ray, and the presence or absence of the pelvic frenum are diagnostic for some adult Coryphopterus (the pelvic-fin frenum is the anterior membrane running from spine to spine that forms the fin into a sucking disk). My DNA barcoding results, however, reveal that pelvic-fin characters do not apply to larvae, recruits, or even small juveniles of several species. For example, the species with divided pelvic fins have fused pelvic fins as larvae and small juveniles (i.e. C. alloides, C. personatus, C. hyalinus, and C. lipernes). The pelvic frenum can be present in juveniles of species that later do not have one (C. dicrus) and the innermost pelvic-fin rays do not become distinctly shorter or longer until well after the transitional stage.
Transitional sand gobies can develop their metamorphic melanophores in differing sequences, leading to a proliferation of transitional larval types that certainly represent the same species. At least some of this variation may reflect the marked variability in the degree of markings with habitat types, with lightly-marked juveniles living on white sand and those on darker backgrounds or more turbid waters being heavily-marked. The light marking may occur in larvae as well, where a significant portion of individuals are missing the melanophores on the caudal-fin base and/or the dorsal caudal peduncle. If these patterns prove to occur within the same species, it raises a very interesting question whether larvae have pre-determined which habitat to settle onto or the trait is flexible.
species: #dorsal/#anal-fin elements #pectoral rays (pelvic-fin form), sand or other goby
10/10 group (widespread and abundant species) C. glaucofraenum: Randall: 10/10 pect 17-20 Bohlke: 10/10, rare 9 pect 17-20 usu 19 C. tortugae: Acero: 10/10 pect 18-20 C. bol: Victor 2008: 10/10 pect 18-20 C. eidolon: Randall: 10 (11 is a typo)/9-10, mode 10 pect 19-20, rare 18 Bohlke: 10/10, rare 9 pect 19-20 C. thrix: Bohlke: 9-10/10 pect 17-19 C. dicrus: Randall: 10/10 pect 18-20 Bohlke: 10/10 pect 18-20 11 group (localized endemics) C. punctipectophorus: Bohlke: 11/10 pect 18-20 (South Carolina to the Gulf of Mexico) C. venezuelae: Cervigon: 11/11 pect 18-20 (NE Venezuela: Cubagua, Isla Margarita, and Cumana) fewer than 10 (widespread, but notably uncommon) C. kuna: 9/9 pect 15 C. alloides: 10/9 Bohlke: 10, rare 9/9, rare 8 pect 16-17 (divided pelvic fins)
C. lipernes: 10/10 pect 16-18 (divided pelvic fins) C. hyalinus: 10/10 pect 14-16 (divided pelvic fins) C. personatus: Randall: 11/11 pect 14-16 (occ. 10/10) Bohlke: 10-11, mode 11/10-11, mode 11 pect 14-16 (divided pelvic fins)
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Group 5: divided pelvic-fin gobies .
These two large genera include many of the abundant small gobies ubiquitous on and around Caribbean reefs. They share six first-dorsal-fin spines and 9, 10, or 11 dorsal and anal-fin elements. The larvae of these gobies are typically small and lightly marked, usually with only a ventral midline series of melanophores (at the isthmus, pelvic-fin base, anal-fin base and caudal peduncle). The larvae of this group and the seven-spined short-fin gobies (Group 3) can appear similar; although, with the characters discussed here, they should all be able to be identified, at least to genus.
The large genus Coryphopterus dominates this group of gobies and accounts for the vast majority of gobies one sees on a Caribbean coral reef. The largest group within Coryphopterus are the sand gobies. These fishes can be found perching on the bottom along the sandy edges of hard substrate, seemingly everywhere except in the most turbid or muddy environments. The sand gobies are particularly difficult to identify to the species level in the field and, even when in the hand, careful examination of marking patterns is required to distinguish the species. This becomes even more difficult for smaller juveniles that have not developed their species-specific marking patterns. The other group of Coryphopterus, the hovering masked and glass gobies, are also very abundant, although more reef-associated. They are found in large groups just off the bottom on almost every coral reef in the region.
The Lythrypnus gobies are much less conspicuous, but may also be quite abundant on reefs. Their larvae can be difficult to separate from those of Coryphopterus
The small lightly-marked goby larvae account for a major fraction of larval collections in the region. They are superficially quite similar, sharing the ventral midline markings and an otherwise unremarkable appearance. Before counting fin rays, the basic appearance of the larvae can distinguish the three most common genera. The larvae below are from a typical collection: Coryphopterus personatus in the middle, Lythrypnus nesiotes below, and Microgobius signatus above. The body shape of each is distinctive: Coryphopterus larvae tend to be hunched-over, Lythrypnus are usually not hunched-over and have a slightly wider body with a shorter caudal peduncle, and larval Microgobius are long and straight with a blunted upward-facing mouth and a sharply-tapering caudal peduncle.
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Group 2: six-spined shortfin gobies 2 .
Group 3: seven-spined shortfin gobies .
Group 4: longfin gobies .
Group 5: divided pelvic-fin gobies .
Bathygobius, Lophogobius, Priolepis, Awaous, and Sicydium
This group of six-spined gobies with short median fins and fused pelvic fins includes several unrelated genera of gobies, including tidepool, reef, and fresh-water species. Although common in their appropriate habitats, this group of gobies are not usually observed or photographed on reefs. The abundant reef and sand gobies of Coryphopterus and Lythrypnus are separated for convenience and treated in Group 2.
Goby larvae are typically the most abundant larvae collected in most reef fish larval collections, both in diversity and often in total numbers. Indeed, Ctenogobius saepepallens, the dash goby, is the most frequently occurring larval type in my Panama collections, followed closely by the bridled gobies, Coryphopterus spp.
Since the process of elimination is critical to the identification of larval gobies, the diversity within this group makes for some difficulty in species ID. A variety of other factors add to the complexity of identifying goby larvae:
The larval melanophore patterns within the family tend to be conservative, with many larval types sharing a sparse basic pattern of a ventral midline series of melanophores: at the isthmus, pelvic-fin base, anal-fin base, and caudal peduncle. Melanophore patterns can be quite variable within types- many individuals, especially earlier-stage larvae, are missing one or a few of the standard complement for their type.
Melanophores can be contracted, appearing as discrete dots, or expanded into either complex dendritic star-shapes or linear forms. Linear melanophores often merge with adjacent melanophores into long streaks. In addition, the intensity of melanophores can vary a great deal, with many preserved larvae showing faint or indistinct melanophore patterns (in some species this variation is
The soft fin-ray counts often vary by at least one or two in Caribbean gobies, unlike many other reef fish families that have very conservative fin-ray formulas. In addition, the reported modal fin-ray counts from different sources in the literature can sometimes vary, usually by one ray. Nevertheless, modal fin-ray counts are critical to species diagnosis.
The oft-used character of six vs. seven spines in the first dorsal fin is sometimes difficult to see (since the seventh spine is tiny). Although it is often not that useful for practical screening of larvae, the number of spines can be very useful for genus diagnosis, separating genera with otherwise similar appearances and fin-ray counts. There is some variation in dorsal spine counts; but it is helpful to recognize that six-spined gobies usually have five close spines and then a distant sixth, while seven-spined gobies have five close spines and then two more spaced out farther. Thus some of the variants can be recognized as anomalous (i.e. four close and two spaced out is likely a variant seven-spined goby).
A common problem is that some literature sources count total dorsal-fin spines and total dorsal-fin soft-rays, confusing whether the spine count is including the first, often spinous, element of the second soft dorsal fin. It is best to count total elements in the second-dorsal and anal fins to avoid this problem (and the issue of whether the first element of the second-dorsal fin and anal fin in some gobies is spinous or soft, which... surprise, can also vary).
Larval gobies tend to initiate transformation from larval to juvenile phase (also transition, or metamorphosis) while still pelagic and many transitional individuals can be collected in waters over the reef. Indeed, in some collections, the majority of specimens are in transition. As a result, larval goby samples can often include a surprisingly wide range of morphological appearances.
Head Shape: The head shape of transitional gobies varies greatly. Pre-transformation goby larvae usually have thin pointed heads with terminal mouths. As they initiate transformation, the head usually thickens and the snout often becomes more rounded. In those species with blunt head-profiles, this change can be marked and the mouth can move subterminally. (photographs below of larval Gobionellus oceanicus transitional series)
Eye Shape: The eye shape can change radically during transition and the process is somewhat consistent within larval types. Both the shape itself and the size at which the changes are observed can be an important character for species identification. As larvae initiate transformation, narrowed eyes become round, tilted eyes become vertical, and in some species the eye becomes markedly larger (in a few it gets smaller, e.g. larval Nes longus). Eye shapes can thus be valuable for inferring the stage of goby larvae, i.e. in a species with narrowed eyes in pre-transitional larvae, the presence of round eyes in a small individual indicates that it is in transition. This becomes particularly useful in practical larval sorting where the size at which larvae develop round eyes can be an important character, as in Lythrypnus vs. Coryphopterus. (photograph at right of transitional changes in the eyes of larval Lythrypnus nesiotes)
Body Shape: The body of pre-transitional larvae is typically thin and becomes thicker and bulkier at transition. This change needs to be distinguished from effects of condition of larvae. Clearly some emaciated larvae appear very thin and narrow. This appearance can be found in some larvae with round eyes and even metamorphic melanophores, indicating that they are not just immature early-stage larvae.
The fins of those species who develop long pectoral and pelvic fins as juveniles show a marked increase in the length of these fins at transition. In a few cases, where juveniles have a characteristically short fin, that fin length may decrease at transformation.
There is variation in the timing of changes in the early life history of gobies; some larval gobies develop transitional morphological changes, especially rounded eyes and blunted snouts, before acquiring any transitional markings, as in the larval Lythrypnus at right. In contrast, it is common with larval gobies to see individuals of the same species and in the same collection that have started to develop metamorphic melanophores while still morphologically in mid-transition, at least in body and head shape. However, the eyes of larval gobies almost always start rounding before transitional markings develop; it is exceptionally rare to see a larva with dense metamorphic melanophore patches and narrow eyes. Two larvae at the ends of the spectrum easily look like they could be different species.
Metamorphic Melanophores: These arrays of additional melanophores (along with leukophores and iridophores) are usually smaller and limited to the skin surface, compared to the large, discrete, and often deeply-penetrating larval melanophores. In many other reef fish families, the metamorphic melanophores are typically in dense patches that often begin on the head and develop posteriorly following the pattern of the juvenile markings of the species. In gobies, however, the size difference of the melanophores is less obvious, and metamorphic melanophores can often be just as large as larval melanophores and are distinguished mostly by their graded appearance, i.e. the accumulation of more markings in a pattern starting around the mouth and head, then at the caudal peduncle and dorsal midline, and then filling in from forward to rear (photographs below of a transitional series of Bathygobius soporator). This phenomenon helps a great deal in providing missing links for species IDs, but also contributes to the confusing variety in the appearance of larval types. This is especially the case when the metamorphic melanophores can show up in very different sequences, as is common in larval Coryphopterus glaucofraenum.
Of course there is some variation in the size of larvae within a species. There can be two sources of this variation and distinguishing between them is important.
One is the simple size increase with growth and development during the early life history: younger and less-developed larvae are smaller than older ready-to-settle larvae. This variation can be detected by the well-known ontogenetic landmarks to be expected with growth, i.e. first the flexion of the notochord, then the full development of the fin-ray elements and finally the eye and head shape changes as settlement approaches. Among the late-stage larvae collected over reefs, almost all have passed the flexion stage and have developed their full complement of fin rays. The subsequent body and eye-shape changes and the degree of development of metamorphic melanophores are the features that vary most in these settlement-stage larvae.
The second source of variation is individual variation in size at the same stage of development. This variation can be large in gobies, and, of course, the observed range increases with sample size. This variation can be confusing, and the occasional extreme size variant can look like a different species entirely. For example, the photograph at right shows the extreme one percent variation in size at transformation for the common Coryphopterus glaucofraenum larval type. Note that these are all transitional larvae that have already developed round eyes. The larval sizes in the photograph range from 5.1 to 8.6 mm SL, but 90% of the larvae of this species that I have collected are concentrated between 6.5 and 7.3 mm SL.
Larval eye morphology
Larval gobies of different species and different stages of development exhibit a remarkable variety of shapes of the eyeball, most often a narrow vertical oval but, in some species, irregular or even squared. These eye shapes, along with other eye-related morphological features, likely reflect adaptations to the pelagic world of reef fish larvae, either to degrees of darkness or differing wavelengths of light. Fortunately, these shapes tend to be consistent within species and can be used as characters to help identify larvae.
The primary variations are in eyeball shape, most often a narrowed vertical oval, but sometimes squared or another irregular shape. The oval sometimes can show a pronounced tilt, usually forward, but sometimes backward. The direction of the tilt is not always consistent within larval types, for example larval Evorthodus lyricus commonly show tilts both forward and backward (this is true to a lesser degree for larval parrotfishes, family Scaridae, as well as the wrasses of family Labridae). As a rule, the eyes of larval gobies become fully round at the end of the settlement transition.
In addition, there can be indentations in the iris, usually, but not always, dorsal and/or ventral. Many very early-stage larvae of all kinds of fishes show these indentations as part of the development of the eyeball, but in larval gobies these indentations can persist, sometimes through transition. Persistent indentations in various quadrants of the iris can be a consistent character for certain larval types. The photograph below left shows a persistent dorsal iris indentation in a 9.6 mm SL transitional larva of Ctenogobius saepepallens. The photograph below right shows a 5.5 mm SL Bathygobius curacao larva with persistent off-center-axis dorsal and ventral indentations of the iris despite being in transition.
Another occasional feature of the eyeball of larval gobies is the presence of an additional speckled membrane overlying the black surface of the upper iris. This feature is mostly consistent within larval types and can thus aid in identifications. In several larval goby types, this membrane is visibly lifted off from the eyeball. In some species the speckled membrane is only along the top quarter of the eyeball, while in others it extends further down, usually overlying the posterior half of the iris. At right, the oblong-shaped eyeball of a 7.2 mm SL larval Coryphopterus glaucofraenum shows the distinctly speckled membrane overlying the upper and rear of the iris.
A very common feature in the eyes of larval gobies is an extension of the shiny iris in the posterior-inferior quadrant. The extension appears to have a more flattened appearance than the rest of the iris. In some larval types this extension is quite prominent. Some rare individuals show clearly abnormal outgrowths of the eyeball in this same quadrant, perhaps a developmental anomaly related to whatever might be the function of this extension. The photograph at left shows a 6.9 mm SL larval Coryphopterus glaucofraenum with the abnormal outgrowth.
A rare feature in some larval gobies is a bizarre outgrowth of tissue from the eyeball into the adjacent compartments of the head. Interestingly, in Microgobius signatus this can occur in several individuals in the same collection, suggesting that whatever is causing the anomaly may be an environmental effect. The photograph below shows the head of an 8.0 mm larval Microgobius signatus.
Gobies are perhaps best known for their fused pelvic fins that act as a sucking disk to anchor them to the substrate. The degree of fusion of the pelvic fins and the overall shape of the disk are important characters in gobioid taxonomy, although the feature is certainly far more labile than taxonomists would desire. Unfortunately the degree of concordance between larvae and adults in pelvic-fin morphology is still an open question. In my collections, it is clear that the presence or absence of divided pelvic fins can differ between larval and adult stages, as in Coryphopterus personatus.
There are several basic states of pelvic-fin morphology in larval gobies. The pelvic fins on the right and left can be completely separate, with the base of the innermost fin ray clearly separated by a space from the base of the ray on the other side. This state is typical of most fishes (including the gobioid sleepers of the family Eleotridae), but is quite uncommon in gobies. The pelvic fins can be divided down to the base, or only partially-divided, leaving the proximal innermost fin rays still fused (as in larval Gobulus myersi, pictured at left). Alternatively, the pelvic fins can be completely fused along the length of the rays; this is the most
common condition among the larval gobies. Lastly, within the completely-fused pelvic-fin group, there can be a frenum, or anterior connecting band, joining the outermost pelvic-fin spines on the two sides to form a cup-shaped fin. This cup can be flat and inconspicuous, as in the 9.9 mm SL larval Ctenogobius saepepallens at right, or an obvious large sucking disk as in the 7.7 mm SL larval Elacatinus saucrus pictured at the top of this section.
The gobies are the largest family of reef fishes and account for a major fraction of the world's tropical marine fish fauna. There are well over a hundred Caribbean species, and doubtless a few more to be described. In addition, there are numerous cryptic species among the gobies in the western Atlantic (populations with sharply divergent DNA sequences that are usually allopatric, but can be sympatric). Although almost always small and inconspicuous, gobies occur in large numbers in all reef-associated habitats. There are over 30 regional genera and, unfortunately, many groupings of closely related species that make species-level larval identifications particularly challenging. I have managed to identify and include in this guide the larvae of almost all of the shallow-water goby genera of the region; a few deep-water genera remain unknown.
The great taxonomic diversity of gobies is certainly reflected in their early life history stages. Larval gobies exhibit the full range of larval sizes at transition, from about 4 mm to almost 30 mm SL. In general, however, they are small and nondescript with a long, narrow, and thin body. They tend to have small to medium-sized terminal mouths, small heads without spines, and slender flexible spines in the fins. They can be recognized most readily by their two separated dorsal fins with the first having only a few spindly spines. In addition, they often have fused pelvic fins and typically light markings. The basic marking pattern for goby larvae is a ventral midline series of melanophores: at the isthmus, pelvic-fin base, anal-fin base, and caudal peduncle, along with a variety of other small melanophores. Some larval gobies also have markedly narrowed and tilted eyes. Since Caribbean goby genera are often quite speciose and the larvae only become distinct during transition or even later, some groups will certainly require DNA testing for the identification of individual larvae to the species level.
Since there are too many Caribbean species to deal with on one webpage, the goby family needs to be subdivided, a task that has tested more than a few fish taxonomists and can be quite frustrating. A variety of divisions have been proposed in the past, none of which have been satisfactory and certainly none have been backed up by strong phylogenetic evidence. Gobies are highly variable in morphology and genetics and deep phylogenies so far are quite elusive. Suffice to say, some traditional separations based on the state of fusion of the pelvic fins and the presence or absence of pores and scales are not reflective of true relationships. Indeed, the state of the pelvic fins can be variable among larvae of obviously close relatives. The evolutionary loss of pores and scales is an individual adaptation and not likely a shared attribute among relatives. Larval markings in gobies are often sparse and the basic patterns are generally shared by unrelated groupings and do not fall out in manageable blocks. Since genetic relatedness is an unwieldy method to subdivide larval forms in a group this complex, I have tried to arrange the groups in a form that makes it easier to navigate. The basic separations I use are six vs. seven first-dorsal-fin spines, the short and long-fin groups, i.e. the increasing number of median-fin rays, and the fusion state of the pelvic fins. The number of dorsal-fin spines, six vs. seven, is not always easy to see on larvae, but is consistent enough to be useful and seems a natural separation among gobies. The number of dorsal and anal-fin soft rays is somewhat consistent within similar-appearing larvae and the "long-fin" gobies with more than 11 second-dorsal and anal-fin elements are usually easy to distinguish from the "short-fin" gobies, typically with 9, 10, or 11 second-dorsal and anal-fin elements. Lastly, although pelvic-fin states can be phylogenetically labile, the state of fusion is often an obvious visible attribute of goby larvae and the division of the pelvic fins seems to be a characteristic of a set of goby species as well as the allied gobioids, the eleotrids and ptereleotrids.
Gobies are found worldwide in fresh, brackish and saltwater. They are concentrated in the tropics and subtropics, mainly of the Indo-Pacific, but some marine species can be found in the subarctic streams of southern Siberia. Gobies have been transported beyond their natural range via the intake pipes or ballast water of large ships. One species, Neogobius melanostomus, a native of the Black and Caspian Seas, was introduced into one of the Great Lakes in North America around 1990 and has since spread into all five. Between 1960 and 1963 two marine gobies native to Japan, Korea, and China had established populations along the California coastline and by 1980 they were established in several parts of Australia.
Biogeographic Regions: nearctic (Introduced , Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Introduced , Native ); oceanic islands (Native ); indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )
Other Geographic Terms: island endemic
Most gobies are extremely small; in fact, the smallest known vertebrate is a goby from Japan, no longer than 10 mm at sexual maturity. The largest, Gobioides broussenetii from the Caribbean, may reach 50 cm TL. Gobies are usually recognized by their small size, the existence of two dorsal fins (the first with eight flexible spines and the second soft), and a blunt round head with large eyes. Some gobies have prominent head barbells as well. Most gobies, and all freshwater species, have pelvic fins united to form an adhesive or sucking disc. However, some reef species have separated pelvic fins although the degree of separation is highly variable. The scales may be cycloid, ctenoid, or absent and the lateral line is absent. (Click here to see a fish diagram).
Coloration in gobies ranges from vivid, especially in reef species like the brilliantly marked neon gobies, to drab, as in many estuarine species (Bathygobius). Still others may be pallid or translucent (Coryphopterus). Although most reef gobies are sexually monomorphic in terms of permanent coloration and gross morphology, temporary sexual dichromatism (color differences between the sexes) has been observed during courtship and spawning on reefs and other habitats. When permanent sexual dimorphism does occur, it may vary even within a genus. For instance, males in some genera, Lythrypnus and Coryphopterus, have longer dorsal and/or anal spines than females, but other species within these genera lack any morphological differences. Permanent sexual dichromatism also exists in some species but investigators have been unable to explain why there is such variation within genera.
Many gobies have evolved unique physical adaptations for life in tidal or estuarine environments. For instance, mudskippers, which span the genera Boleophthalmus, Periophthalmus, Periophthalmadon, and Scartelaos, are essentially amphibious. The skin contains numerous blood vessels enabling them to take up atmospheric oxygen and a muscular tail helps them to skip over the mud. Additionally, their eyes are perched high on the head to allow them to forage effectively and avoid predation. Another goby, Gillichthys mirabilis, has evolved a highly vascularized buccopharynx, which allows it to gulp air from the surface when the waters it inhabits become depleted of oxygen.
Other Physical Features: ectothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike; male larger; sexes colored or patterned differently; male more colorful; sexes shaped differently; ornamentation
Diagnosis: A larval type with D-?,10 A-9. Unfortunately, the 10/9 fin-ray count is the most common formula for Caribbean gobies and there are many candidates for this larval type. The basic melanophore pattern, i.e. a melanophore at the angle of the jaw, a row along the anal-fin base continuing to the start of the lower procurrent caudal-fin rays and melanophores at the base of most of the lower segmented caudal-fin rays, is shared with larval Barbulifer ceuthoecus and the six-spined Coryphopterus. The body shape of this larval type, however, does not match the Coryphopterus. In most features, this larval type fits with what would be expected for immature B. ceuthoecus larvae, i.e. the pattern of melanophores (especially the post-pelvic Y), the small round eye, the flattened head shape with a very broad mouth, and the relatively wide caudal peduncle. However, the melanophore just forward of the vent on the abdominal promontory is not found on other B. ceuthoecus larvae, and this larval type is therefore described separately (pending intermediate individuals or DNA sequencing). Barbulifer antennatus is not reported from Panama, but cannot be excluded.
Analogues: (light markings with anal fin plus caudal peduncle row) Within the diverse anal fin plus caudal peduncle row group, there are many very similar larval types. Two of the most common gobiid larval genera share this basic marking pattern, including the melanophore at the angle of the jaw: Lythrypnus (without the caudal-fin melanophores) and Coryphopterus (both six-spined). A few Elacatinus are the only seven-spined gobies to share the anal-fin-caudal peduncle row of melanophores, but, as a rule, they do not have the melanophore at the angle of the jaw. All three of the aforementioned groups are typically wider-bodied and do not share the flattened head appearance and broad mouth of this larval type. Furthermore, their eyes are either narrowed vertical ovals or large and round, without the smaller slightly flattened eye exhibited by this larval type. They do not share the post-pelvic Y marking and only a rare Coryphopterus specimen exhibits an abdominal promontory melanophore. Typical Barbulifer ceuthoecus larvae are larger, usually more than 9 mm SL, and thicker (but may represent the mature version of this larval type).
Analogues: (VMS4: jaw angle, thorax, anal fin, caudal peduncle) The basic larval melanophore patterns on the sand gobies are shared with a number of other gobies, although, in general, these others do not have equal numbers of dorsal and anal-fin elements as do most of the sand goby species. Coryphopterus personatus larvae do have the equal numbers of fin elements, but are missing the melanophores at the jaw angle and at the caudal-fin base and have a larger eye. Larval Lythrypnus appear quite similar, but have 10/9, are shorter and wider, have fewer procurrent caudal-fin rays, and transition at a smaller size. Lophogobius cyprinoides may share the VMS4 pattern, but have 10/9 and fewer procurrent caudal-fin rays. Bathygobius larvae have 10/9 and VMS4, but have distinctive internal melanophores not present on larval Coryphopterus The seven-spined gobies with similar larvae do not have the jaw angle melanophores and the caudal peduncle streak extends only halfway to the caudal fin.
Gobies are extremely successful in their ability to exploit microhabitats inaccessible to most other fishes; they are found from subarctic streams in Siberia to mountain streams at altitudes of 2,000 m on islands to ocean depths of 800 m. On coral reefs, they can be found in the numerous cracks and crevices or out in the open among corals (Gobiosoma). Others build burrows (Signigobius) or use the burrows of invertebrates, ranging from polychaete worms to clams. Members of the genera Boleophthalmus, Periophthalmus, Periophthalmadon, Scartelaos, and Bathygobius have uniquely adapted to tidepools, mudflats and mangrove swamps, where some even climb out of the water for extended periods to forage (discussed further in Food Habits). Still others build numerous holes along sandy beaches (Coryphopterus) or compose a large part of the fishes in estuaries, inland seas and continental shelf environments as deep as 800 m.
The approximately 200 species found in freshwater form a separate category of gobies. Gobies are extremely successful in freshwater habitats where few other fish are found, such as oceanic islands. Half of the freshwater species are part of the subfamily Sicydiinae. Members of this group exhibit a high degree of island endemism and some even reach the headwaters of high-elevation rivers (2,000 m) in mountains. Some species have a short marine life-stage while others have evolved to live completely within freshwater environments.
Habitat Regions: temperate ; tropical ; saltwater or marine ; freshwater
Aquatic Biomes: pelagic ; benthic ; reef ; lakes and ponds; rivers and streams; temporary pools; coastal ; abyssal ; brackish water
Other Habitat Features: estuarine ; intertidal or littoral
Gobies are classified as zooplanktivores, omnivores, and carnivores, as they feed on a wide variety of small organisms like crabs, shrimps, smaller crustaceans (such as copepods, amphipods, and ostracods), mollusks, annelids, polychaetes, formaninferans, sponges, small fishes, and eggs of various invertebrates and fishes. Many gobies are quite selective in their feeding habits, favoring an individual prey item, such as a minute algae or small invertebrate. Others have evolved unusual adaptations to allowing feeding in habitats formerly off-limits to fish. For instance, mudskippers (Boleophthalmus, Periophthalmus, Periophthalmadon, and Scartelaos) take on an amphibious character, actively foraging over mudflats and up mangrove roots for crustaceans and insects (see Physical Description for more information on this). Members of the genus Gobiosoma are well known for their brilliant colors used to distinguish them as cleaner fishes. These gobies feed on the parasites and dead skin of larger fish. Some freshwater species of the subfamily Sicydiinae are amphidromous: the larvae are carried downstream to the ocean where they feed and grow (they travel for feeding, not reproduction, unlike many other fishes) before migrating back to freshwater island habitats.
Primary Diet: carnivore (Piscivore , Eats eggs, Eats non-insect arthropods, Molluscivore ); herbivore ; omnivore ; planktivore
Gobies are extremely important in almost any ecosystem they occupy because their relative abundance makes them an essential part of the food chain. Gobies have the greatest impact on the benthic environment since most reside there. Gobies may be the keystone species (dominant in the food chain) in the freshwaters of small oceanic islands because they are often one of the few species of fish that exist in these areas.
Ecosystem Impact: keystone species ; parasite
Species Used as Host:
- Branched Corals
- Sea Urchins
Due to their small size, gobies must be wary of many different predators, such as sea snakes, shore birds and larger fishes. It’s no surprise that they have developed a wide range of behaviors to defend themselves. Perhaps the most characteristic feature of gobies is their secretive nature. They rarely leave their burrows and display a wide range of coloration for camouflage. Some gobies are translucent and have only a few colored spots to match their surroundings while others have formed symbiotic relationships with shrimp. In the latter case Crytocentrus steinitzni sits outside the burrow watching guard while the shrimp clears out the burrow they share. Cleaner fishes of the genus Gobiosoma enjoy relative freedom from predation due to their color pattern and cleaning behavior. Others live within sponges, sea urchins, the branches of corals, or the roofs of caves for protection. Some gobies even rely on chemical protection, producing a poison called tetrodotoxin, which also occurs in pufferfishes and species of salamander. Some morphological adaptations can be found in mudskippers (Boleophthalmus, Periophthalmus, Periophthalmadon, and Scartelaos). The eyes of mudskippers are located on the tops of their heads to detect and avoid shore birds as well as to locate prey, and their powerful tail allows them to move quickly along the mud.
- larger fish (Actinopterygii)
- sea snakes (Hydrophiidae)
- shore birds (Charadriiformes)
Anti-predator Adaptations: aposematic ; cryptic
Based on studies in:
Puerto Rico, Puerto Rico-Virgin Islands shelf (Reef)
This list may not be complete but is based on published studies.
Known prey organisms
Based on studies in:
Puerto Rico, Puerto Rico-Virgin Islands shelf (Reef)
This list may not be complete but is based on published studies.
Life History and Behavior
There is considerable evidence that gobies use visual, tactile, chemical, auditory, or olfactory cues in reproduction and territorial behavior (see Reproduction and Behavior). It is quite likely that investigators will find more evidence of different types of communication as research progresses.
Communication Channels: visual ; tactile ; chemical
Other Communication Modes: pheromones
Perception Channels: visual ; tactile ; chemical
In most gobies, eggs hatch in one to five days and grow rapidly within a few days. At hatching the larvae are quite advanced with pigmented eyes, well-developed jaws, digestive tracts, and vertical fin folds. The small transparent larvae (between 2 and 10 mm long) are usually dispersed in the water column where they swim for three to 20 days. Finally, the larvae settle into a suitable habitat and develop colors that allow them to blend in with the surroundings. They reach sexual maturity within a few months. However, in temperate climates development may take much longer, with sexual maturity occurring after one to two years.
A notable exception to this developmental pattern (and there are likely many others) can be found in burrowing gobies. In this species, the male remains in a burrow, which is sealed shut by the female, for up to five days. During this time, the burrow is periodically reopened and the eggs cleaned by both male and female before the male is again sealed in the burrow. The eggs develop entirely within the burrow and only one juvenile apparently exits the burrow, suggesting that juveniles receive nourishment through cannibalism, as well as food reserves and their surroundings. Upon exiting, the juvenile immediately begins a benthic existence.
Tropical gobies develop very quickly and probably live no longer than one year but in cooler areas some species may live between two and ten years.
Gobies exhibit a wide variety of mating systems but most seem to be promiscuous, either organized into a hierarchical social system, such as Coryphopterus personatus, or small territories maintained by individuals, such as Coryphopterus glaucofrenum and Lythrypnus dalli. A typical mating sequence begins with nest preparation by the male, which involves clearing and cleaning the area where eggs will be deposited. In response, the ventral area of the female swells and the male proceeds to swim back and forth between the female and nest site and in some cases the male will nudge the female with its snout. The male may also make exaggerated swimming motions in place by anchoring himself with the sucking disc.
There is evidence of monogamy in some gobies (Ioglossus spp., Gobiodon spp., Valencienna spp., Gobiosoma spp., and Paragobiodon spp., among others) but some of these pairings are the result of fierce territorialism toward other members of the same sex, which confines mating to that individual. However, there is evidence that some gobies recognize mates as individuals (Elacatinus oceanops), possibly through olfactory cues. In fact, extensive research on frillfin gobies has revealed a complex suite of visual, chemical, auditory, and olfactory cues used in courting behavior. For instance, an ovarian pheromone produce by female frillfin gobies has been shown to elicit courtship in males, even if the female is not present. Male frillfin gobies have also been observed making a knocking sound to initiate courtship. An example of visual cues is well illustrated by the alamo’o, which is found in the Hawaiian Islands. In this species, the male attracts females by perching on a rock and waving its rear end, which is bright yellow, back and forth in the current. Although there are very few studies as extensive as these for all gobies it is likely that a mixture of visual, tactile, chemical, auditory, or olfactory cues will be found in other gobies as well.
Mating System: monogamous ; polygynous ; polygynandrous (promiscuous)
Most gobies have extended spawning seasons with peak spawning depending on the species, but in colder regions breeding may only occur once or twice a year. Females may deposit from five to several hundred eggs, which the male then fertilizes. Some gobies exhibit protogynous hermaphroditism, such as members of the genus Paragobiodon. Individuals may be found in pairs, trios, or male-dominated harems depending on the species. In Paragobiodon harems the largest individual is always the dominant male and the second largest the functional female, and sex change is socially controlled. Most likely, similar hermaphroditism will be found in other territorial and pair-forming gobies. In estuarine species the lunar cycle is thought to play a role in spawning behavior as well as larval recruitment.
Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sequential hermaphrodite (Protogynous ); sexual ; fertilization (External ); oviparous
In most cases, male gobies guard the eggs after they are fertilized. The young probably stay close to adults for a period of time after hatching. Even if females are permanently paired, they rarely take part in parental care. In some freshwater island species parental care is not practiced at all. For instance, in the subfamily Sicydiinae the larvae are carried downstream to the ocean where they feed and grow before ascending the freshwater streams.
Parental Investment: male parental care
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimens with Sequences:6357
Specimens with Barcodes:6184
Species With Barcodes:692
There are five critically endangered gobies, 18 listed as vulnerable, and 12 listed as low risk. Agricultural practices and the introduction of non-native species are some important causes for their decline. This is not surprising considering the diversity of this family and the fact that many are confined to a single lake or river system, or one or few islands. Some may go extinct before humans become aware of their existence.
Relevance to Humans and Ecosystems
No specific information was found concerning any negative impacts to humans.
In the Caribbean and Philippines amphidromous gobies (see Food Habits) form a large portion of the catch as they migrate upstream in freshwater creeks. A number of gobies have been successfully bred in captivity, and some are also popular in the aquarium trade.
Positive Impacts: pet trade ; food
Gobies are fishes of the family Gobiidae, one of the largest fish families comprising more than 2,000 species in more than 200 genera. Most of them are relatively small, typically less than 10 cm (4 in) in length. Gobies include some of the smallest vertebrates in the world, such as Trimmatom nanus and Pandaka pygmaea, which are under 1 cm (3/8 in) long when fully grown. Some large gobies, such as some species of the genera Gobioides or Periophthalmodon, can reach over 30 cm (1 ft) in length, but that is exceptional. Generally, they are benthic, or bottom-dwellers. Although few are important as food for humans, they are of great significance as prey species for commercially important fish such as cod, haddock, sea bass, and flatfish. Several gobies are also of interest as aquarium fish, such as the bumblebee gobies of the genus Brachygobius. Phylogenetic relationships of gobies have been studied using molecular data.
- 1 Description
- 2 Distribution and habitat
- 3 Subfamilies
- 4 Ecology and biology
- 5 Reproduction
- 6 Behavior
- 7 Commercial importance
- 8 See also
- 9 References
- 10 External links
The most distinctive aspects of goby morphology are the fused pelvic fins that form a disc-shaped sucker. This sucker is functionally analogous to the dorsal fin sucker possessed by the remoras or the pelvic fin sucker of the lumpsuckers, but is anatomically distinct; these similarities are the product of convergent evolution. Gobies can often be seen using the sucker to adhere to rocks and corals, and in aquariums they will stick to glass walls of the tank, as well.
Distribution and habitat
Gobies are spread all over the world in tropical and temperate near shore-marine, brackish and freshwater environments. Their range extends from the Old World coral reefs to the seas of the New World, and includes the rivers and near-shore habitats of Europe and Asia. On coral reefs, gobies constitute 35% of the total number of fishes and 20% of the species diversity. Gobies are generally bottom-dwellers and live inside the bodies or burrows of invertebrates.
Gobiidae contains six subfamilies:
Members of the subfamily Amblyopinae are elongated mud-dwelling gobies commonly known as the eel gobies or worm gobies. Their two dorsal fins are connected by a membranous structure and their eyes are highly reduced. They are usually pink, red, or purple in coloration. Amblyopinae contain 12 genera and about 23 species.
Members of Benthophilinae are endemic to the Ponto-Caspian region (including the Marmara, Black, Azov, Caspian, and Aral Seas). The representatives of the subfamily have fused pelvic fins and elongated dorsal and anal fins. They are distinguished from the closely related subfamily Gobiinae by the absence of a swimbladder in adults and location of the uppermost rays of the pectoral fins within the fin membrane. Its members include tadpole gobies, monkey gobies, and bighead gobies.
Members of Gobiinae are known as true gobies. It is the most widespread and most diverse of the subfamilies under Gobiidae, containing around 2000 species and 150 genera.
Members of Gobionellinae mostly inhabit estuarine habitats, though some are freshwater and a single genus, Gnatholepis, is marine. They are found in tropical and temperate regions around the world with the exception of the northeastern Atlantic Ocean, the Mediterranean Sea, and the Ponto-Caspian region. It includes around 370 species and 55 genera.
Members of Oxudercinae are commonly known as mudskippers. They are highly specialized members of the family. They are able to survive for extended periods on land through a combination of behavioral and physiological adaptations, including pectoral fins that act as simple legs; the ability to breathe through their skins (like frogs); and the digging of damp burrows to avoid drying out. Mudskippers live in tidal areas, particularly on mudflats and in mangrove forests, and are only found in tropical and subtropical regions.
Ecology and biology
Gobies are primarily fish of shallow marine habitats, including tide pools, coral reefs, and seagrass meadows; they are also very numerous in brackish water and estuarine habitats, including the lower reaches of rivers, mangrove swamps, and salt marshes. A small number of gobies (unknown exactly, but in the low hundreds) are also fully adapted to freshwater environments. These include the Asian river gobies (Rhinogobius spp.), the Australian desert goby (Chlamydogobius eremius), and the European freshwater goby Padogobius bonelli. Most gobies feed on small invertebrates, although some of the larger species eat other fish, and a few eat planktonic algae.
Gobies attach their eggs to a substrate, such as vegetation, coral, or a rock surface. They lay from five to a few thousand eggs, depending on the species. After fertilizing the eggs, the male guards the eggs from predators and keep them free from detritus. The male fans the eggs, thereby providing them with oxygen. The female maintains the burrow. The eggs hatch after a few days. The larvae are born transparent, and they develop coloration after spreading to find a suitable habitat. The larvae of many freshwater goby species are carried downstream to the brackish waters, or even to the sea. They return to fresh water weeks or months later.
Gobies in warmer waters reach adulthood in a few months, while gobies in cooler environments reach adulthood in two years. The total lifespan of goby varies from one to ten years, again with the species in warmer waters generally living longer.
Gobies usually live in male-female pairs that construct and share burrows, similar to many other fish such as Mozambique tilapia. The burrows are used for shelters and spawning places. Gobies use their mouths to dig into the sea bottom, removing dead coral-fragments, rubble, and benthic algae in order to build their burrows. Gobies maintain their burrows by fanning away sand inside the burrows. Furthermore, gobies use coral rubble to block burrow entrance. A single goby carry as many as nine pieces of coral rubble per minute. Gobies also build a 6–13 cm high mound over the entrance of their spawning burrow. The mound lets the water flow fast over the mound. The water flow created by the mound helps to provide oxygen to the eggs. While burrow building is a cooperative behavior done by both sexes, males usually put more effort in burrow maintenance than females. Females feed more instead, because the reproductive success is optimal when females put more energy in preparing for the reproduction. Interestingly, after spawning eggs, the roles of male and female changes. Females primarily maintain the burrow, and males mainly care for the eggs by fanning them, thereby providing oxygen. When females leave the burrow, however, the mounds lose their heights. The males then give up on the eggs and eat them, preparing for future mating opportunities. Goby burrows vary in size depending on the size of the goby species.
Kleptogamy refers to the sneaking behavior during reproduction. Female gobies prefer male gobies with large bodies. Since not all males have large bodies, the smaller ones may cheat instead of expending energy to find mates. The sneakers wait near the spawning ground of paired gobies. The sneakers then release their sperms on the spawning ground as soon as the paired female releases her eggs. Even though sneakers’ sperms fertilize some eggs, the paired male cannot distinguish the eggs fertilized by the sneakers from those fertilized by his own sperms. Therefore, the paired male equally gives parental care to all the eggs.
Kleptogamy is a good strategy in many ways. First, the sneakers do not need their own territories, indicating that they do not need to spend energy in protecting territories, as most other males do. Most male gobies need their own territories, since females will not choose to mate with a male who does not own his own territory. Secondly, the sneakers do not provide parental care to their eggs. The paired males will provide parental care instead of the sneakers. Therefore, the sneakers can save energy, and they can put more effort into finding new targets for cheating.
The cost of kleptogamy is that the sneakers can receive aggressive attacks from the paired males that are usually much larger and stronger than the sneakers. For small sneakers, the attacks by the paired males can be detrimental and often lead to death.
The sneakers are also referred to as pseudo-females, since they are small and hardly distinguishable from females. This small body size makes cheating easier. The paired males would, most of the time, think that the sneakers are females, and thus the paired males would not chase the sneakers away. The paired males are called “bourgeois” males, because they are larger, stronger, and most importantly, paired.
A few species of goby, such as blackeye goby and Lythrypnus dalli, can change their sexes. Sex change is possible in these gobies, since the external genitalia for males and females do not differ much. Sex changes can take from days to weeks. Most sex changes in gobies are from female to male (protogyny) rather than male to female (protandry). Female-to-male changes are observed not only in gobies but also in wrasses, damselfishes, and sea basses. Female-to-male change usually occurs because the resident male of the group is dead. If there is no male in the group, reproduction will be impossible. Therefore, the dominant female turns into male, allowing mating to happen. Male-to-female change occurs when the females have preference for specific features in males. For example, female gobies prefer large males, and a few large males mate with multiple females, whereas small males lose their chance to mate. Small males either choose to become sneakers (kleptogamy) or choose to transform into females because all females technically have high mating opportunities. By turning into females, males can ensure that they produce many descendants.
Some gobies have extraordinarily developed sex change ability. Gobiodon histrio from the Great barrier Reef exhibits bi-directional sex changes. Gobiodon histrio is one of the very few species that can change sex in both ways. It has been shown that when two Gobiodon historio females, used to be males, are on the same coral reef, one of them transformed back into a male goby.
Sex determination in coral goby Gobiodon erythrospilus does not occur until juvenile gobies meet potential mates. Confronting a potential mate can be difficult for Gobiodon erythrospilus juveniles, since most coral resources, crucial for attracting mates, are occupied by pre-existing paired gobies. Juveniles can only meet potential mates when one member of the pre-existing pairs dies. Juveniles’ sexes are determined according to the sexes of their potential mates. When a juvenile goby meets a female, it becomes a male, and vice versa. This type of sex determination is referred to as socially-influenced sex determination.
Some gobies remember landmarks that are within short distances, and use them to find their ways. Small frillfin gobies (Bathygobius soporator) live in intertidal zones. They swim through the pools during high tides and memorize how each pool connects to the others. Then, during low tides, they can exhibit accurate jumping behaviors, as they have memorized the paths. In a new environment, these gobies do not show jumping behaviors or jump into wrong pools. Nevertheless, after one night, they show the same accurate jumping behaviors.
A study was done to understand how gobies react to changing habitat. Gobies were given two choices: a safe habitat with less food and a dangerous habitat with more food. Results from both the full and hungry gobies revealed that gobies, when confronted with the trade-off between foraging and avoiding predation, made choices that would better their foraging.
Gobies sometimes form symbiotic relationships with other species, such as with burrowing shrimps. The shrimp maintains a burrow in the sand in which both the shrimp and the goby live. The shrimp has poor eyesight compared to the goby, but if it sees or feels the goby suddenly swim into the burrow, it will follow. The goby and shrimp keep in contact with each other, the shrimp using its antennae, and the goby flicking the shrimp with its tail when alarmed. These gobies are thus sometimes known as "watchmen gobies" or "prawn gobies". Each party gains from this relationship: the shrimp gets a warning of approaching danger, and the goby gets a safe home and a place to lay its eggs. Only the alpha male and female reproduce, other fish in the colony eat sparingly to resist being eaten by the alpha male or female. This way, only the largest and fittest are able to reproduce.
Another example of symbiosis is demonstrated by the neon gobies (Elacatinus spp.). These gobies, known as "cleaner gobies", remove parasites from the skin, fins, mouth, and gills of a wide variety of large fish. The most remarkable aspect of this symbiosis is many of the fish that visit the gobies' cleaning stations would otherwise treat such small fish as food (for example, groupers and snapper). Again, this is a relationship where both parties gain: the gobies get a continual supply of food as bigger fish visit their cleaning stations, and the bigger fish leave the cleaning stations healthier than they were when they arrived.
Another form of symbiosis exists between gobies and the mushroom coral Heliofungia actiniformis (Fungiidae), in which representatives of the genus Eviota roam among the tentacles possibly hiding from predators.
Gobies have commercial importance in Ukraine. They are fished in the Sea of Azov, northwestern Black Sea. Most important species are round goby, monkey goby, toad goby, and grass goby. The grass goby is also a commercial fish in Italy.
In the aquarium
Several species of gobies are kept in aquaria. Most captive gobies are marine. Perhaps the most popular is the small but colorful neon goby. Most gobies stay toward the lower portion of the aquarium, hiding in the rockwork, but some species (most notably the shrimp gobies) prefer to dig themselves little burrows. Aquarists typically provide them with a fine-grained substrate to prevent damage to their delicate undersides. Commonly kept saltwater species include the Randall's shrimp goby, and watchman goby.
- Sleeper gobies are a closely related family (Eleotridae) that lack the fused pelvic fin sucker typical of most gobies, but are otherwise very similar in size, shape, and ecology.
- Blennies are a group of shallow-water marine fish often confused with gobies.
- Dragonets are superficially similar to gobies and sometimes confused with them.
- Pholidichthys leucotaenia is commonly called the engineer goby or convict goby, but is not a goby.
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