Digestive enzymes and parasitology of Nile tilapia juveniles raised in brackish biofloc water and fed with different digestible protein and digestible energy levels

Biofloc technology (BFT) system is increasing around the world and Nile tilapia is suggested as the major fish species for such technology. The objective of this study was to evaluate diets with different levels of digestible protein (22, 26 and 30% DP) and digestible energy (3000, 3150 and 3300 kcal kg(-1)) for Nile tilapia juveniles raised in brackish biofloc system water (10 ppt) and its effects on the activity of digestive enzymes and the presence of ectoparasites in the gills. Tilapia juveniles (1.25 +/- 0.15 g of initial weight) were stocked in thirtytwo experimental units (100 L tanks) with 15 fish per tank. After 42 days fish were harvested, sampled and analyzed. The pepsine (stomach) and trypsine (intestine) activities significantly increased according to the increase of dietary levels. For both cases the higher activity was observed in 30% DP treatment (P < 0.05), with (pepsine) and without interaction (trypsine) with digestible energy levels. The opposite trend was observed for chymotripsine activity (intestine), in which 22% DP presented the higher activity, with significant interaction with energy levels. The higher activity for intestinal lipase activity was observed in 3150 kcal kg(-1). No difference was found for ectoparasite analyses in gills between the treatments. Although in all treatments monogea type was found (70-90% of prevalence), the number of parasites per fish was low in all treatments (< 1.6 parasites fish(-1)). The results suggested that differences in dietary digestible protein and digestible energy affected the activity of digestive enzymes in Nile tilapia juveniles raised in biofloc with 10 ppt of salinity. On the other hand, biofloc system did not promote ectoparasite spread even with low dietary levels of digestible protein and digestible energy.