LARVAL REARING OF COCKLE Cerastoderma edule (GMELIN, 1791) IN A RECIRCULATING AQUACULTURE SYSTEM

The cockle Cerastoderma edule is an economicall y, societally and culturally valuable species in several European  countries, however, nowadays stocks are threatened by disease and sub-optimal management. Hatchery production of juveniles for release is a major contributor to strengthen the stock and consequently improve the  sustainability of the natural stocks.

This study developed culture procedures to recover exhausted cockle beds and to increase cockle production where required, namely by determining the feasibility of rearing  C. edule larvae in a recirculating aquaculture system (RAS), compared with the traditional larval rearing methodology (Batch) and to compare the larval rearing in  RAS with different larval densities (10 and 30 larvae per mL) .

Ten days after fertilization, the mean survival and  growth of  C. edule  larvae was higher (30.7 1%;  166 ± 3 µm) than in the Batch system (14,7%; 154 ± 4,1 µm) ,  at the density of 7 larvae per mL. In the RAS system, t he larval survival was affected by the initial density (10 larvae per mL - 79,9 ± 28%; 30 larvae per mL - 33.8 ± 23%), especially during the metamorphosis. At day 11 after fertilization, over 70% of larvae reared in the RAS system presented foot , while in Batch the percentage was much lower (49%). The physical, chemical and microbiologic parameters suggested that the tested densities were not excessive  to disturb the biofilter stability of RAS.

The  C. edule larval rearing performed at high larval stocking densities in RAS system present a reduction in the operating costs to produce this species. The larval rearing in RAS system can contribute positively to the promotion of restocking programmes based on hatchery produced settle larvae, namely for injection into seawater column. The advant ages of RAS system also benefit the seed production for aquaculture in commercial parks.