Recirculation nursery systems for bivalves

In order to increase production of bivalves in hatcheries and nurseries, the development of new technology and its integration into commercial bivalve hatcheries is important. Recirculation aquaculture systems (RASs) have several advantages: high densities of the species can be cultured resulting in a cost-effective production system; optimal temperature maximizes production and allows rapid turnover of the product; stable water quality improves growth rate and minimizes stress and potential loss by diseases. Pilot RAS systems were developed for seed rearing of oysters (Crassostrea gigas), scallops (Pecten maximus), mussels (Mytilus edulis) and clams (Ruditapes decussatus). Optimal feed addition and waste matrix were determined. Based on this, system flow rates were designed. Seed growth in the pilot RAS systems was compared at different renewal rates and with growth in flow-through systems (FTS). All four species can be reared in RAS and showed similar growth in RAS and in FTS or in RAS with a higher renewal rate. RAS can keep O₂, nitrogen and pH within the desired range. Temperature was generally higher in RAS than in FTS, probably due to heat induced by the pump circulating the water. The supply of sufficient amount of food in combination with a desire to reduce the renewal rate calls for use of concentrated feed in RAS.