Expressão gênica, atividade enzimática e desempenho de larvas de tilápia do Nilo alimentadas com níveis de proteína bruta na dieta

Abstract

The aim of this study was to determine the crude protein requirement in larvae of Nile tilapia (Oreochromis niloticus), evaluating performance, gene expression and activity of digestive enzymes and stress by exposure to air (Re). Diets containing: 30, 36, 42% and 48% crude protein (CP) were formulated. The animals were fed four times daily. Animal samples were collected at 10, 20 and 30 days of experiment. At 30 days, the resistance to air exposure was evaluated. For the gene expression, the neuropeptide Y (NPY), pepsinogen, trypsinogen, chymotrypsinogen, carboxypeptidase and cholecystokinin (CCK) genes were evaluated. The activity of the enzymes trypsin, acid proteases and chymotrypsin were determined. The data were submitted to normality and homogeneity tests. Survival was not influenced by the CP levels in the diet (P> 0.05). After 10 days of feeding, CP levels affected performance, and above 36% CP levels are indicated in the first 10 days of larval rearing. Gene expression of pepsinogen was also affected at 10 days, being greater than 30% CP, intermediate to 42% CP and lower than 36 and 48% CP (P <0.05). From the 20 days of feeding, levels between 30 and 42% PB are indicated for better performance. Diets did not affect gene expression and enzymatic activity in this phase (P> 0.05). At 30 days of feeding, the gene expression and activity of the enzymes, CCK and NPY were influenced by CP levels in the diet, except for the expression of pepsinogen. The highest expression and enzymatic activity were detected at the 42% CP level in the different enzymes, CCK and NPY, except for pepsin activity, which was higher at levels of 42 and 48% PB (P <0.05). Regarding the stress test, the animals showed similar Re in the two air exposure times tested (5 and 7 minutes), regardless of diet. However, when comparing the times for each protein level, the diet with 36% CP provided the same Re regardless of the time tested (P> 0.05). The other levels tested had higher Re at 5 minutes (P <0.05). Thus, different levels of crude protein affect performance, resistance to stress, gene expression and enzymatic activity during Nile tilapia larviculture. The results suggest that the PB level to be used depends on the larval period of this species.