Effects of a free amino acid mixture in replacing dietary fishmeal and reducing Nile tilapia<i> (Oreochromis</i><i> niloticus)</i> production costs

Abstract

To encourage aquaculture sustainability and lower fish production costs, fish products need to be substituted with sustainable ingredients in aquafeeds. Toward this goal, we examined whether a natural mix of highly concentrated free amino acids could alleviate the negative effects of low-fish meal (FM) diets on Nile tilapia in terms of growth performance and nutrient utilization. In the present study, a 2 x 3 factorial design with two FM levels (5 % and 10 %) was used to prepare the experimental diets and three levels of Kera-Stim (R) 50 (KS), a free amino acid mixture, was supplemented (0 %, 0.25 %, and 0.5 %). Nile tilapia fish (average initial body weight of 20 g) were cultured in 18 cages and provided with one of the six diets for eight weeks. We found that dietary KS supplementation significantly increased the growth performance parameters including final body weight, weight gain, and specific growth rate compared with the diets without KS supplementation (P < 0.05). Moreover, KS supplementation had a substantial positive effect on the feed conversion ratio (P < 0.05). Interestingly, not only the low-FM diets but also the diets supplemented with KS had a positive effect on the economic conversion ratio and economic profit index, suggesting increased economic efficiency. Furthermore, lysozyme, catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase activity levels were significantly increased by supplementing low-FM diets with KS (P < 0.05). KS and low-FM diets increased the whole-body levels of ash, fat, and crude protein (P < 0.05). Moreover, KS supplementation increased the levels of polyunsaturated fatty acids, such as arachidonic acid (20:4 n6) and docosahexaenoic acid (C22:6 n3). We concluded that supplementing a natural free amino acid mix to a low-FM diet can mitigate negative nutritional effects and achieve optimum fish performance without compromising growth performance or revenue-to-cost ratios.