Effects of raw corn starch levels on growth, feed utilization, plasma chemical indices and enzyme activities in juvenile yellowfin seabream Sparus latus Houttuyn

Abstract

A 10-week growth trial was conducted to evaluate the effect of raw corn starch levels on the growth, feed utilization, plasma chemical indices and metabolic enzyme activities of juvenile yellowfin seabream Sparus latus. Four semi-purified experimental diets with different raw corn starch levels (5%, 10%, 20% and 26%) and a high-protein control diet were prepared before the experiment and hand-fed to triplicate groups of juvenile yellowfin seabream Sparus latus. Weight gain and specific growth rate for fish fed the diet containing 26% raw corn starch were significantly lower than those for fish fed 10% or 20% corn starch diets or the high-protein control diet. Fish fed 10% or 20% corn starch diets had a slightly better growth performance than those fed the 5% corn starch diet. Feed efficiency ratio and protein efficiency ratio (PER) for 20% raw corn starch fed fish were the highest among all groups, although no statistically significant differences were found among the experimental groups. The high-protein control group had a significantly lower PER value than other groups. Protein productive values for fish fed the 5% raw corn starch diet and the high-protein control diet were significantly lower than those of fish fed the 20% raw corn starch diet, but not significantly different from the values of any other group. The values of intraperitoneal fat ratio, viscerosomatic index and condition factor, as well as body and muscle compositions, were unaffected by corn starch levels. The hepatosomatic index and liver glycogen level for fish fed 5%, 10%, 20% raw corn starch and the high-protein control diets were equal but significantly lower compared with that of fish fed the 26% raw corn starch diet. Plasma values of the fish were not affected by various dietary treatments, except that a significantly higher plasma glucose concentration was measured in the high-protein control group compared with the values in the other groups. There were variations in the activities of hepatic hexokinase and pyruvate kinase of the yellowfin seabream after they had been fed different dietary raw corn starch levels for 10 weeks. The overall results showed that a 20% inclusion level of raw corn starch in the diet was better utilized by juvenile yellowfin seabream than 5%, 10% or 26% levels and had a protein-sparing effect.