CORN GLUTEN AND MEAT AND BONE MEALS AS PROTEIN-SOURCES IN DIETS FOR GILTHEAD SEABREAM (SPARUS-AURATA) - NUTRITIONAL AND HISTOLOGICAL IMPLICATIONS

Two experiments were conducted to compare the effect of the partial su bstitution of fish meal by two different protein sources, corn gluten (CGM) and meat and bone meals (MBM) in diets for juveniles gilthead se abream. Growth, feed efficiency, protein efficiency ratio and protein productive values were not significantly affected by the source of die tary protein, although higher values were observed with diets containi ng increasing levels of meat and bone meal. No differences were found in fish proximate composition at the end of the experiment. Histologic al studies of liver tissue showed no liver alteration in fish fed diet s including increasing levels of corn gluten meal. On the contrary, an increased deposition of lipids, nuclei polarization and isolated necr otic focus were found in hepatocites of fish fed diets exceeding 20% o f meat and bone protein. Apparent protein digestibility (ADC) in diets containing CGM showed similar results to those obtained with the cont rol diet. However, a significant reduction in digestibility was observ ed when MBM was used as partial substitute of fish meal protein. A neg ative correlation between dietary ash content and protein digestibilit y was observed. Higher amounts of nitrogen were excreted as levels of CGM and MBM increased in the diets, being significantly higher in the case of 40% substitution either with CGM or MBM protein. (C) 1997 Else vier Science B.V.