New Guinea Slender Mudskipper

Distinguished by the following characteristics: total D2 elements 27-30; caudal fin length 21.4-27.9% SL; head length 22.0-25.7% SL (Ref. 5218).

Amphidromous. Refers to fishes that regularly migrate between freshwater and the sea (in both directions), but not for the purpose of breeding, as in anadromous and catadromous species. Sub-division of diadromous. Migrations should be cyclical and predictable and cover more than 100 km.Characteristic elements in amphidromy are: reproduction in fresh water, passage to sea by newly hatched larvae, a period of feeding and growing at sea usually a few months long, return to fresh water of well-grown juveniles, a further period of feeding and growing in fresh water, followed by reproduction there (Ref. 82692).

Dorsal spines (total): 7; Dorsal soft rays (total): 24 - 29; Analspines: 1; Analsoft rays: 23 - 28

Inhabit mainly tidal mudflats adjacent to turbid, brackish rivers.

Pseudapocryptes confluentus

USNM 217952, Holotype, Fly 75–31, 35.2 mm.

USNM 217305, Paratype, Fly 75–30, 45.3 mm.

USNM 217306, Paratypes, Fly 75–31, 24: 14.8–37.9 mm.

Pseudapocryptes confluentus is readily distinguished from all previously described Oxudercinae (= Apocrypteinae) in having the distal ends of fin rays of first dorsal, second dorsal, caudal, and anal fins joined by a single continuous fin membrane. First dorsal fin with 6 spines, at least in some specimens (sixth spine reduced, not reaching margin of fin membrane); second dorsal fin I 29–31; anal fin I 28–31; pectoral fin 20–21, lowermost 7–9 rays thickened; total caudal fin rays 21–24 (about 15 principal caudal rays). Dorsum of head including snout, cheeks, gill cover, and most of body covered by minute scales; about 140–180 scales in a lateral series and 100 predorsal scales. Isthmus, breast, ventral surface of abdomen, base of pectoral and pelvic fins, and caudal fin scaleless. Dentition basically identical in specimens 15–45 mm: each side of upper jaw with 2–3 large, elongate conical teeth anteriorly, then a single row of about 20 much smaller conical teeth extending posteriorly almost to rictus; each side of lower jaw with a single large, erect, inwardly curved canine tooth or fang internal to symphysis, and a single row of 10–12 (usually 11) large, subhorizontal conical teeth; posterior one-third of lower jaw toothless. Color in preservative (similar in all or almost all respects to that in life): body more or less uniformly dark brownish dorsally and laterally; side of abdomen with about 6 oblique dark bands; ventral surface of head and abdomen pale (not purple or blood red in life); all fins hyaline.

Pseudapocryptes confluentus agrees with Pseudapocryptes Bleeker, 1874 (type-species Eleotris lanceolatus Bloch and Schneider, 1801, by original designation), in having a more elongate body and smaller scales than any other known Apocrypteinae, similar fin formulae, and basically similar dentition. Pseudapocryptes lanceolatus differs from P. confluentus in having second dorsal and anal fins separated from caudal fin; jaw teeth fewer; more than 200 (up to 350) scales in a lateral series; and small scales covering isthmus, breast, base of pectoral and pelvic fins, abdomen, and proximal two-thirds of caudal fin.

I have examined a well-preserved series of 55 juveniles and subadults of P. lanceolatus from the Sunder-bans, Bangladesh, California Academy of Sciences 40081 (formerly Stanford University Natural History Museum same catalog number), 26.8–117 mm, as well as two somewhat larger specimens from Thailand, USNM 119991, 167 mm, and USNM 119636, 186 mm. In these specimens there is no membranous connection between second dorsal fin or anal fin and caudal fin; membrane from last spine of first dorsal fin extending posteriorly to base of first ray in second dorsal fin; caudal fin with a series of thin oblique color bars; each side of upper jaw with 5–7 large teeth anteriorly and 6–8 smaller teeth posteriorly, and each side of lower jaw with a large canine tooth behind symphysis and 8–15 large subhorizontal teeth. In the specimens from Bangladesh the sides of the body have about a dozen irregular oblique color bars, sometimes breaking up into spots, and better defined on the posterior half of the body than on the anterior half. These bars are more distinct in the juveniles than in the subadults, but traces of them are evident in all 55 specimens.

Hundreds of P. confluentus up to about 50 mm (juveniles?) were observed at the type-locality on a gently sloping, flat, detritus-littered mudbank exposed at low tide (Fly 75–31). They were flipping about in a manner and with a level of activity suggestive of Periophthalmus, except that they invariably landed on their sides and flipped from their sides, never balancing on their pelvic fins or assuming an upright position.

Zappa confluentus, the New Guinea slender mudskipper, is a mudskipper endemic to New Guinea, where it is only known from the lower parts of the Fly, Ramu and Bintuni Rivers. It is found on mudflats adjacent to turbid rivers. This species can reach a length of 4.4 centimetres (1.7 in) SL.