Some Effects of Salinity and Temperature on Early Development and Survival of the English Sole (Parophrys vetulus)

Abstract

Eggs of the English sole were incubated at a number of salinity–temperature conditions within the ranges of 10–40‰ salinity (S) and 2–12 C. Temperatures of 2 C were lethal in all cases. Development time from fertilization to 50% hatch ranged from 3.5 days (12 C) to 11.8 days (4 C) and was shortest at salinities around 25‰ between temperatures of 6–12 C. Larvae were classified as viable (normal) or abnormal on the basis of several subjective criteria.Response surfaces were computed and salinity–temperature conditions were estimated at which several responses were maximized, namely: larval size: 28.1‰, 7.9 C; total hatch, 25.6‰, 9.0 C; viable hatch, 25.9‰, 8.4 C. In general, optimum conditions for survival appeared to be associated with salinities and temperatures of 25–28‰ and 8–9 C. Temperatures associated with the production of 50% viable hatch or better at optimum salinity conditions (25.9‰) were calculated to be those bounded by 4.5 and 12.5 C.Incidental observations were obtained in several cases on egg density and oxygen consumption. At 30‰ S, 6 C, eggs floated for about 93% of the incubation period and sank just prior to hatching. Salinities of neutral buoyancy of these eggs rose from 27.8‰ at fertilization to 30.8‰ at hatching. Oxygen consumption tests and calculation of rates of oxygen transfer to the eggs indicated that rates of development were independent of oxygen availability in all tests.Several inferences are drawn from the experimental evidence regarding effects of salinity and temperature on distribution and abundance. Over the geographic range of the species, salinity would appear to have little influence on egg viability. Temperature, however, may limit abundance at the northern and southern boundaries of the range of commercial exploitation by lowering egg viability, and be lethal to eggs near the boundaries of geographic distribution.