Work

A combined in situ–ex situ assessment of fish feed fate and associated carbon emissions

Year: 2026

Type: article

Abstract: Aquaculture plays a key role in addressing the global protein demand. However, its long-term sustainability depends on minimizing its environmental impacts, particularly eutrophication and greenhouse gas (GHG) emissions. The fate of fish feed that is not ingested by the fish remains an overlooked factor, yet it is crucial for accurately assessing the carbon footprint of fish production. To assess the fate of undigested fish feed under different conditions, we used complementary in situ and ex situ approaches to separate the effect of feed composition from the influence of pond conditions. First, we performed an in situ experiment to investigate the breakdown of four common fish feed types, and secondly, quantified their associated carbon dioxide (CO 2 ) and methane (CH 4 ) production in an ex situ experiment. We explored potential drivers, including feed physicochemical properties. Results showed that the feeds varied significantly in their properties (CN ratio range: 5.4–10.7; decay constant k range: 0.023–0.05 h −1 ). This variation was critical: feeds with lower physical stability and lower CN ratios disintegrated fastest. In ex situ incubations, CO 2 production significantly increased with the addition of all feed types compared to controls that contained only fishpond sediment (±15 nmol g −1 h −1 ). Conversely, CH 4 production was minimal across all treatments even under anoxic conditions. Our findings indicate that while feed decomposition directly stimulated CO 2 production, it did not constitute a determining factorin CH 4 production in this system. Critically, we show that feed physicochemical properties, particularly physical stability and CN ratio, are key regulators of the rate of these microbial processes. To effectively reduce aquaculture's carbon footprint, future development must embed precision feeding (i.e. prevention of overfeeding), along with improved feed composition and stability, into comprehensive GHG mitigation strategies. • Methane (CH 4 ) emissions from fish feed are negligible under both oxic and anoxic conditions. • Rapid feed decomposition reveals its key role in carbon cycling within aquaculture systems. • Feed addition increases CO 2 flux, but emissions do not reflect net greenhouse gas input. • High-protein feeds (low C:N) degrade faster and alter tank biogeochemistry. • Feed-derived carbon is rapidly mineralized, highlighting the importance of feed composition in aquaculture assessments.

Source: Journal of Cleaner Production

DOI: 10.1016/j.jclepro.2026.147711