Fisiologia, metabolismo e desempenho de linhagens de Tilápia alimentadas com dietas contendo níveis de proteína

Abstract

The objective of this study was to evaluate the performance, activity of proteolytic enzymes and the gene expression of digestive enzymes and appetite regulating hormones in two tilapia strains fed diets containing levels of crude protein (CP). In experiment I, 240 Nile tilapia juveniles (Oreochromis niloticus) (16.56 ± 1.21 g) were fed three times a day for 65 days. In experiment II, 240 juveniles of red tilapia (Oreochromis sp.) (29.32 ± 5.19 g) were fed twice a day for 42 days. In both experiments, four isoenergetic diets were formulated to have 24, 30, 36 or 42% of CP. Each diet was fed to five different tanks (100 L; 12 fish/tank), using a total of twenty tanks in each experiment. Data were submitted to analysis of variance, polynomial regression analysis (experiment I) and Tukey's test (experiment II). In experiment I, the increment of CP resulted in a linear decrease in animal performance and protein and energy retention rates, and a linear increased in hepatic alanine aminotransferase activity. A positive quadratic effect of CP on pepsinogen (P < 0.05) was observed, although acid protease activity was not affected (P > 0.05). Trypsinogen and trypsin activity in the intestine presented similar patterns, showing a positive quadratic response to dietary protein levels (P < 0.05). A linear increase in intestinal chymotrypsinogen expression was observed, but the activity of chymotrypsin showed a positive quadratic response (P < 0,05). The expression of cholecystokinin (cck) and peptide yy (pyy) increased linearly with increasing CP (P < 0.05). The results of experiment II indicated that the diet with 42 % CP was associated with the highest expression of pepsinogen and the lowest activity of acid protease (P < 0.05). The expression of hepatopancreatic trypsinogen increased as CP levels in the diet increased up to 36% (P < 0.05), whereas trypsin activity showed a significant reduction with 42 % CP (P < 0.05). The diet with 42 % CP was associated with the lowest intestinal chymotrypsinogen expression and the lowest chymotrypsin activity (P < 0.05). The α-amylase expression decreased with increasing (P < 0.05) CP levels up to 36 %. No significant differences were observed in the expression of procarboxypeptidase, lipase and leptin among all the groups (P > 0.05). The diet with 42 % CP resulted in a decrease (P < 0.05) in the expression of ghrelin and insulin and an increase (P < 0.05) in the expression of cck and pyy. Genes involved in regulating digestion and appetite are modulated by dietary protein in a similar way in both tilapia strains.