The sepiids are benthic or benthopelagic. The young resemble the adults when they hatch and are also benthic. The sepiids have large eggs which are stored in the oviduct. During spawning the eggs are coated with oviducal gland secretion, then with nidamental gland secretion and the female deposits them singly on a substrate (see Boletzky, 1983). The duration of embryonic development depends upon temperature.
The young hatch with a yolk reserve that allows them to survive for a few days in the absence of food. When food, especially mysids, is available, the hatchlings begin to attack immediately. Swimming prey are seized by the tentacular clubs. Benthic prey, such as crabs, are pounced upon and seized with the arms. While crustacea are the main prey in younger Sepia, subadults and adults also eat fishes (Guerra, 1985; Castro and Guerra, 1989, 11990).
Growth is fast. The conversion rate is 30 to 40% (Pascual, 1978). In warm waters, animals grow faster and mature at a smaller size than those living in cold (temperate) waters. The shell or cuttlebone grows by adding new chambers bounded by lamellae (the septa of the striated zone) which are visble on the posterior ventral surface of the cuttlebone. In tropical species, a chamber may be formed daily so that the number of septa corresponds to the age in days. In temperate water however, it takes two to three days for a new chamber to be completed. Sepia officinals hatches with a cuttlebone of about 10 septa (Boletzky, 1983).
Spawning takes place over a prolonged period of time or throughout the year. Spawning is intermittent (Boletzky, 1975; Mangold et al., 1993). The number of mature eggs found in the ovary at any one time is not an indicator of fecundity. In Sepia officinalis the total of laid eggs surpasses by several times the holding capacity of the ovary. The endocrine and nervous control mechanisms of reproduction, are complicated (Boucaud-Camou et al., 1994).
Spawning migrations exist in temperate water species but are often absent in tropical ones. The European cuttlefish, Sepia officinalis migrates south-north (Atlantic Ocean, North Sea) or offshore-inshore (Mediterranean) for spawning. The life-span of sepiids varies between a few months and 1 to 2 or 3 years according to the adult size and the environment (temperature, food availability).