Nutrient retention capabilities of Nile tilapia (Oreochromis niloticus) fed bio-regenerative life support system (BLSS) waste residues

Nile tilapia were evaluated as a bio-regenerative sub-process for reducing solid waste potentially encountered in bio-regenerative life support systems. Ten juvenile Nile tilapia (mean weight = 2.05 g) were stocked into triplicate aquaria and fed one of seven experimental diets consisting of vegetable, bacterial, or food waste for a period of seven weeks. Weight gain (g), specific growth rate (mg/d), and daily consumption (g) was significantly higher (p < 0.05) in the control group (13.80, 281.60, and 47.49, respectively) followed by the wheat bran/wheat germ group (4.25, 86.87, and 24.24). Carbon and crude lipid retention was significantly higher (p < 0.001) in fish fed the control diet (37.99 and 68.54, respectively) followed by fish fed the wheat bran/wheat germ diet (23.19 and 63.67, respectively). Nitrogen, sulfur, and crude protein retention was significantly higher (p < 0.001) in fish fed the wheat bran/wheat germ group (40.73, 98.65, and 40.75, respectively) followed by fish fed the control diet (23.68, 21.89, and 23.68, respectively). A general loss of minerals was observed among all groups. Strong associations were observed between crude lipid retention and sulfur retention (r2 = 0.94), crude lipid retention and carbon retention (r2 = 0.92), WG and fiber content of dietary treatments (r2 = 0.92), WG and carbon retention and (r2 = 0.88), WG and lysine content of waste residues (r2 = 0.86), crude protein retention and carbon retention (r2 = 0.84), sulfur retention and crude protein retention (r2 = 0.84), and total sulfur amino acid (TSAA) content of residues and WG (r2 = 0.81). Weaker associations existed between WG and crude lipid retention (r2 = 0.77), crude fiber content and carbon retention (r2 = 0.76), and WG and methionine content of waste residues (r2 = 0.75). Additional research is needed to improve the nutritional quality of fibrous residues as a means to improve tilapia’s ability to utilize these residues as a food source in bio-regenerative support systems.