Growth, consumption, assimilation and excretion in the marine herbivorous fish Cebidichthys violaceus (Girard) fed natural and high protein diets

Abstract

Laboratory feeding trials were conducted to determine the growth and food processing rates and gut retention times of a wild, cool-temperate zone fish fed its simulated summer diet of seaweeds and two higher protein diets more typical of those of carnivorous fishes. When this stichaeid fish, Cebidichthys violaceus (Girard), was fed for 12 wk on a pelleted natural summer diet (10% protein) and on this food modified to make two higher (30 and 50%) protein diets, the fish grew equally fast on the 10 and 50% protein diets but most rapidly on the 30% protein regimen. Rates of food consumption and assimilation and energy consumption were lower for fish on the highest protein diet than for those on the other two diets. The energy assimilation rate was lower for fish on the 10% protein diet than for those on the 30% diet, but neither rate was different from that for fish on the 50% protein diet. Gut retention times were shorter for fish on the lowest protein diet, yet nitrogen consumption, assimilation and excretion rates were not different for fish on the three diets, suggesting that C. violaceus feeds to meet a nitrogen (protein) requirement. That the nitrogen excretion rate did not increase with an increase in dietary protein content may be explained at least in part by the marked decrease in food consumption rates with increase in dietary protein levels.