Effects of Dietary Protein and Energy Sources on Digestibility and Methane Production Potential of Nile Tilapia Feces

Aquaculture intensification increases waste generation, whose composition may influence methane emissions. This study evaluated the effects of dietary protein and energy sources on nutrient digestibility and the methane production potential of Nile tilapia feces. Nine experimental diets were tested in digestibility assays: one reference diet (RD) and eight test diets containing 80% RD and 20% of an animal or plant ingredient. Feces were collected and subjected to batch anaerobic digestion. Soybean meal and meat and bone meal diets showed the highest apparent digestibility coefficients (ADC) for dry matter (84.1 and 82.6%) and energy (87.3 and 87.9%), whereas poultry by-product meal presented the lowest values. Crude protein digestibility ranged from 78.74% for blood meal diet to 94.3% for soybean meal diet. Feces from poultry by-product meal generated the highest methane potential (260.9 L kg−1 VS), whereas blood meal exhibited the highest methane production per unit of COD removed (310.5 mL g−1 reduced COD). After 10 days, poultry by-product meal accumulated the highest biogas volume, while soybean meal and blood meal showed the lowest. Principal component analysis suggested inverse relationships between nutrient digestibility and fecal biodegradability. Overall, dietary composition influenced nutrient digestibility, physicochemical characteristics of fish feces, and their methane generation potential. This integrated assessment suggests that feed formulation could contribute to strategies aimed at reducing the methane generation potential of aquaculture wastes.