Optimal Replacement of Fish Meal Protein by Stick Water in Diet of Sex-Reversed Nile Tilapia (Oreochromis niloticus)

SIMPLE SUMMARY: Only limited information is available on the use of stick water in aquafeed, even though this could confer benefits by providing cost-effective nutrition to aquaculture as well as reducing waste effluents. Therefore, the optimal replacement of protein from fish meal by stick water in the diet of Nile tilapia was investigated in the current study. An 8 month trial was conducted in floating baskets, mimicking the market stage Nile tilapia production in Thailand. Based on the overall results, 20% protein replacement of fish meal by stick water was near optimal, providing superior traits of overall observed parameters relative to the baseline fish meal-based diet. Findings from the current study suggest that stick water is a suitable alternative ingredient for sex-reversed Nile tilapia. The pursuit of higher replacement levels while maintaining the carcass quality of reared fish could be a topic for further study. ABSTRACT: The effects of replacing fish meal (FM) protein with stick water (SW) were investigated during the market stage of sex-reversed Nile tilapia, Oreochromis niloticus (18.49 ± 0.31 g initial body weight). The FM protein was replaced with SW for 10% (10SW), 20% (20SW), 30% (30SW) and 50% (50SW) of the FM. The completely randomized design was conducted in outdoor 15 floating baskets (1.5 × 1.5 × 2 m), comprising three replications with 50 fish each, over an 8 month trial. At the end of the experiment, no differences in survival, growth performance or feed utilization were observed across the dietary treatments (p > 0.05). A significant change in lipase-specific activity was caused by the replacement, without changes to trypsin, chymotrypsin or amylase activities. The fish in all dietary groups exhibited normal liver histopathology, but the fish fed a diet containing SW showed higher numbers of cells accumulating lipids as compared to fish fed the baseline 0SW dietary treatment. Hematological parameters were similar across the five dietary groups. Only fish fed the 20SW diet had superior carcass quality compared to the baseline 0SW group, in terms of crude protein and lipids, but lower or higher replacement levels had negative effects on carcass quality. Findings from the current study support the replacement of FM protein with SW at a level of 20% in the diet of sex-reversed Nile tilapia reared to the market stage. Higher replacement levels might be possible with the supplementation of fatty acids.