Fish-processing residues represent a significant environmental challenge due to their high moisture and nitrogen contents, which favor greenhouse gas (GHG) emissions during degradation. This study evaluated how different waste management strategies affect GHG emissions from fish waste, including conventional composting (Bulk), composting amended with biochar (BulkBioch), burial with soil (S), and burial with soil plus sawdust (BulkS). Daily emissions of CH₄, N₂O, and CO₂ were monitored, and cumulative emissions were modeled using generalized additive models. Composting treatments (Bulk and BulkBioch) released higher CO₂, suggesting greater microbial degradation, while burial treatments developed earlier anaerobic conditions with reduced decomposition efficiency. Bulk showed the highest cumulative CH₄ and CO₂ emissions, whereas N₂O fluxes were greater in burial methods, reaching 2.18 g N₂O kg⁻¹ TS in S. Biochar addition was associated with 15% and 10% lower CH₄ and N₂O emissions, respectively, and earlier stabilization of CH4 emissions. In global warming potential, BulkBioch presented the lowest climate impact (305 g CO₂-eq kg⁻¹ fish), followed by Bulk (338 g CO₂-eq kg⁻¹), whereas BulkS reached up to 599 g CO₂-eq kg⁻¹. The use of bulking agents in burial resulted in lower CH₄ buildup and greater nutrient retention. Overall, combining bulking agents and biochar may represent a promising strategy to mitigate GHG emissions while supporting nutrient conservation.

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.

Methane (CH₄) emissions from aquaculture can be enhanced by organic waste accumulation and oxygen-limited conditions, yet field-based emission estimates remain scarce, particularly for intensive tilapia production in above-ground tanks in Brazil. This study evaluated how aquaculture waste composition and oxygen availability affect CH₄ emissions and quantified emissions from a commercial intensive Nile tilapia production system. A controlled experiment assessed water and sediment characteristics and CH₄ emissions during decomposition of feed, feces, and fish carcasses under contrasting residue combinations and aeration conditions. Field measurements quantified diffusive and ebullitive CH₄ fluxes from production tanks and a sedimentation pond during 13 sampling campaigns conducted between February 2023 and November 2024. The non-aerated treatment receiving mixed residues showed the highest CH₄ emissions, whereas aeration reduced mean flux by approximately 98.8%. At commercial scale, emissions were concentrated in the sedimentation pond and dominated by ebullition, while emissions from aerated production tanks were negligible. Annual CH₄ emissions were estimated at 325.9 kg CH₄ ha⁻¹ yr⁻¹, corresponding to 8799 kg CO₂-eq ha⁻¹ yr⁻¹ and 0.147 kg CO₂-eq kg⁻¹ fish produced during the nursery phase. These findings identify oxygen availability and waste accumulation as key targets for CH₄ mitigation through aeration and improved residue management, providing insights into strategies to reduce the environmental impact and support the sustainability of intensive tilapia production.