Early Development and Distribution of the Flathead Sole (Hippoglossoides elassodon)

Abstract

Laboratory studies were conducted on eggs from a southern British Columbia population of Hippoglossoides elassodon. Salinity of neutral buoyancy of eggs decreased from about 25% shortly after fertilization to 17–18% at hatching. The incubation period ranged from 20.9 days (2.36–4.0 C) to 7.2 days (10.65 C). At temperatures of 5.5 C or lower and salinities of 19‰ or lower, larvae tended to hatch at a less advanced stage of development. Mean length of newly hatching larvae increased in successive periods throughout the hatching interval. At mean hatching time, larval length varied from 3.2 mm (15‰, 3.0 C) to 6.3 mm (25‰ 6 C). Larvae from eggs incubated over the range of test conditions (10.42–39.58‰, 2.36–10.65 C) reached a length of 6.9–7.2 mm at yolk exhaustion. Hatching success was highest in trials at 25‰, 6 and 7 C; maximum percent viable hatch is predicted at incubation conditions of 29.16‰, 7.38 C. Posthatching larval survival appeared normal at salinities of about 20–37‰ and temperatures of about 5.5 to >10.65 C. Extensive early larval mortality occurred at salinities of 19‰ or less and at temperatures below 5.5 C. Incipient low lethal temperature levels are estimated to be near 3.5–4.0 C for incubating eggs and 4.0–4.5 C for larvae.Egg and larval characteristics of the experimental material were compared with similar data from the literature on North Pacific Ocean Hippoglossoides. A number of previous distinctions made between eggs and larvae of H. elassodon, H. robustus, and H. dubius require further validation owing to the possible confounding of genetic and environmental influences on the attributes studied. Distribution and abundance of H. elassodon over its North American range is discussed on the basis of the evidence gathered.