Study on carbon budget in small-scale high-density intensive Litopenaeus vannamei aquaculture ponds

The growing global demand for aquaculture products has driven the emergence of ultra-intensive aquaculture systems, which are projected to dominate future aquaculture development. However, comprehensive assessments of carbon budgets in such high-density production models remain limited. This study conducted systematic carbon budget evaluations in two intensive Litopenaeus vannamei aquaculture ponds in Zhejiang Province, China. Our findings reveal that carbon inputs were predominantly attributed to commercial feed (81.87–82.04%), followed by inflow water (16.83–16.87%) and stocking shrimp inputs (0.6–0.7%). Carbon outputs were primarily discharged through effluent water (81.84–84.74%), with harvested shrimp biomass accounting for 15.3–22.2%. Notably, excessive stocking densities were associated with suboptimal growth performance (low growth rates, survival rates, and feed conversion efficiency). The observed feed conversion ratio (FCR) of 1.78 indicates significant resource inefficiency and increased operational costs. When incorporating unaccounted carbon fluxes and energy consumption, we estimated CO₂ emission equivalents of 6.54–6.60 kg CO₂/kg shrimp production. Remarkably, only 8.1–8.9% of emissions originated directly from aquaculture operations, while 91.1–91.8% derived from electricity consumption required for system operation. Key implications include the following: (1) heavy reliance on formulated feeds (> 80% carbon input) coupled with low conversion efficiency (11.1–12.5% carbon assimilation efficiency), (2) elevated carbon loading in effluent (6.4 times influent concentrations) posing environmental risks, and (3) energy consumption constituting the principal carbon footprint component. These findings highlight critical needs for optimizing stocking densities and feeding regimes while maintaining productivity, coupled with the development of energy-efficient practices. Future research should prioritize sustainable intensification strategies that balance production demands with environmental stewardship.