A laboratory-scale recirculating aquaculture system for long-term experimental rearing of bivalves under minimal stress conditions for aquatic animal research

Abstract

Aquatic animal facilities should be designed to minimize stress, ensuring stable environmental conditions that promote animal welfare and enhance experimental reliability. Maintaining bivalves in laboratory tanks with routine water exchange (static-renewal system, SRS) often results in stress and high mortality rates, making long-term rearing challenging. Flow-through systems, while an alternative, require access to seawater and are limited by coastal proximity and regulatory restrictions. Additionally, seasonal collection and transportation of bivalves complicate the consistent supply of animals for carrying out experiments. To address these issues, a simplified recirculating aquaculture system (RAS) was developed to provide stable conditions for bivalves, enabling long-term maintenance with minimal stress for experimental research in aquatic animals. The RAS system integrates culture tanks with solid filtration and biofiltration units to maintain optimal water quality. The RAS was compared to SRS over a three-month rearing period using the bivalve Magallana bilineata. Water quality parameters were assessed every three days, while animal health and mortality were closely monitored. Stress levels were measured by quantitative PCR (qPCR)-based hsp70 mRNA expression. The implemented RAS successfully maintained bivalves with minimal stress and stable water chemistry resulting in only 10% mortality in RAS, whereas it was 80% in SRS. The animals in SRS showed significantly elevated hsp70 expression (p < 0.05), whereas the expression levels were comparable between those in RAS and the wild (p > 0.05). Therefore, the implemented simple RAS significantly improved the welfare of bivalves, reducing mortality and stress, while supporting long-term maintenance and ensuring the suitability for experimental research in aquatic animals.