Effect of body size on growth and food conversion of juvenile striped bass reared at 16–28 °C in freshwater and seawater

Abstract

We conducted two experiments on Shubenacadie River stock of Morone saxatilis fed trout pellets. Experiment 1 compared juveniles of ca. 40 and 550 g initial body weight in hard freshwater (FW) for 73 days at either 20, 24 or 28 °C. Experiment 2 lasting 115 days compared 40, 300 and 800 g fish in either FW or seawater (SW, 30 ppt) at either 16 or 23 °C. Body weight, food intake and food conversion ratio (FCR) responses were analyzed as repeated measures, with initial weight as a covariate. Fish grew well in both FW and SW; however, the final mean weight was slightly higher in FW by 3–14% among all size classes, and significant (P<0.05) only among fish 300 g initial size. Food intake and FCR was independent of salinity. The effect of temperature on growth and FCR differed markedly between body sizes. Whereas 40 g fish reared at 24–28 °C for 115 days attained a final mean weight of 187 g, with an FCR less than 1; at 16 °C, their final mean weight was 75 g and FCR was poor, around three. By contrast, 800 g fish, at 16 °C performed well, gaining about 400 g in 115 days, with an FCR less than 1.8. At 28 °C, growth of fish, greater than 500 g was significantly poorer than at either 20 or 24 °C. The results indicated a marked downward shift in the optimum temperature for growth with increasing body size.