Growth,food conversion and survival of 0-group English sole (Parophrys vetulus Girard) at five temperatures and five rations

Laboratory experiments were conducted to determine the effects of temperature and food ration on growth, conversion efficiency and survival of 0-group English sole (Parophrys vetulus Girard). Young sole, fed a diet of Oregon Moist Pellets, were exposed to constant temperature-ration combinations between 9.5 and 21° C and between 0 and 16% rations (dry weight basis) for a 12-week experimental period. The juvenile sole, initially 4–6 g, grew at a rate of up to 0.95% per day at the most favorable temperature-ration combination, 9.5°C and 16% ration. Highest food conversion efficiency, 10.5%, was observed at the temperature-ration combination of 9.5°C and 8% ration. At 21°C, young sole lost weight at the ration levels fed. Based on growth rate, survival and food conversion efficiencies observed during the experiments and the temperatures to which the young sole are exposed in nature, the temperature at which greatest growth and maximum food conversion efficiency occurs is probably near or below 9.5°C. Although English sole juveniles were maintained for up to 1.5 years on Oregon Moist Pellets primarily, mortality was high during experiments (between 16 and 48%). The high mortality may have been associated with the pellet diet used, which is formulated to meet the nutritional requirements of salmonids and not flatfishes. The microsporidan protozoan Glugea sp., the monogenetic trematode Gyrodactylus sp., and Vibro bacteria also were associated with mortalities during the experiments, and one fish died of a large tumor.