Design and optimization of a recirculating aquaculture system (RAS) for live feed production in aquaculture: a case study using Daphnia magna

Rapid growth in aquaculture necessitates sustainable live feed production, particularly addressing the nutritional needs of fish larvae. Among live feed sources, the freshwater cladoceran Daphnia magna is indispensable due to its superior nutritional quality. However, traditional static culture systems suffer from deteriorating water quality, waste accumulation, and low reproductive efficiency. This study optimized a recirculating aquaculture system (RAS) tailored for D. magna cultivation, considering its sensitivity to environmental fluctuations. The designed RAS incorporates efficient water circulation, biofiltration, and controlled environmental parameters to enhance culture stability and productivity. The effectiveness of RAS was assessed relative to a static system with 50% water exchange (SSWE), based on fecundity, ephippia production, mortality, and stress responses. D. magna cultured in RAS exhibited higher fecundity rates (25 ± 2 embryo per female) and lower mortality (5%) compared to SSWEs (18 ± 1 embryo per female; 15% mortality). RAS maintained superior water quality throughout the study, with stable pH, low ammonia levels, and optimal oxygenation. Furthermore, gene expression analysis of stress-related genes (hsp70 and hsp90) indicated no significant physiological stress under RAS conditions, confirming its environmental stability. Additionally, M-ADaM proved to be the most effective rearing medium for D. magna, minimizing mortality. These findings provide a scalable approach to enhance live feed production for aquaculture while promoting sustainability and environmental responsibility.