Feeding Nile tilapia with varying levels of biofloc: effect on growth performance, survival rate, digestive and liver enzyme activities, and mucus immunity.

The effects of different concentrations of wet biofloc on Nile tilapia, Oreochromis niloticus, were investigated in this study. The aim was to assess the impact on growth, survival, body composition, digestive enzyme activity, liver enzyme activity, and mucosal innate immunity. The experiment consisted of five treatments: a control group (C) which received 100% commercial feed and 50% daily water exchange without biofloc and four treatments where portions of the commercial feed were replaced with wet biofloc (BFT25, 25%; BFT50, 50%; BFT75, 75%; and BFT100, 100%) with limited water exchange. Nile tilapia fingerlings weighing 1.3 g and with a density of 1 ind./L were held for 38 days in fiberglass tanks containing 130 L of water with a salinity of 8 g/L. The results showed that the control group had the highest levels of total ammonium nitrogen (TAN) and nitrite nitrogen (NO2) (P < 0.05). Among the BFT treatments, fingerlings fed with 25% wet biofloc had significantly higher total biomass (741.51 g) and survival (99.74%) (P < 0.05). In terms of carcass quality, the BFT25 treatment had the highest protein (58.77% DW) and lipid (25.06% DW) content. The analysis of bioflocs in the biofloc treatments revealed protein levels ranging from 26.84 to 31.85 (% DW), lipid levels ranging from 1.68 to 2.51 (U/mg protein), and ash levels ranging from 31.85 to 36.44 (% DW). Furthermore, the BFT25 treatment resulted in improved digestive and liver enzyme activity, with the highest levels of protease (17.81 U/mg protein), lipase (2.48 U/mg protein), amylase (80.66 U/mg protein), and liver enzyme ALP (0.176 U/mg protein). In terms of mucosal immunity, the BFT25 treatment exhibited the highest levels of lysozyme (Lys. 34.33 U/mL/min) and immunoglobulin (Ig. 51.66 mg/100 mL), while the BFT100 treatment had the lowest levels (Lys. 17.33 U/mL/min, Ig. 37 mg/100 mL). Based on these findings, it has been demonstrated that Nile tilapia can be fed wet biofloc (developed under the conditions of this study) up to 25% of their commercial feed without compromising their growth performance, survival, body composition, digestive enzyme activity, liver enzyme activity, or mucosal immunity. [ABSTRACT FROM AUTHOR]