Yields of great scallop, Pecten maximus, larvae in a commercial flow-through rearing system in Norway

Survival, growth and yield of competent great scallop (Pecten maximus) larvae were investigated during a full production season in a commercial hatchery in western Norway. Broodstock were collected from natural scallop beds and 12 groups were induced to spawn during the period December 2002 to July 2003. Larvae were reared on a large scale in 36 flow-through tanks (3500 l) at 17 +/- 1 degrees C and continuously fed a mixture of five algal species produced in an indoor continuous-flow system. Large variations in larval performance between spawning groups and tanks were observed, but the results were as good as earlier results using the batch system and prophylactic addition of chloramphenicol. Growth from days 3-24 averaged 4.8 mu m day(-1)+/- 0.8 (sd) and survival 22.4%+/- 21.8 (sd). Mean yield of day 3 larvae was 7.1%+/- 10.0 (sd) and 26.6%+/- 25.9 (sd) for those surviving to day 24. Yield was significantly correlated to larval survival. Larval success was related to initial larval density, algal concentration and season. It was found that the best production regime had an initial larval density lower than 6 ml(-1) and algal concentration of less than 12 mu l(-1) regardless of season. Seventeen tanks met these criteria and produced a mean yield of 0.5 larvae ml(-1) to settlement. Flow-through systems are currently regarded as the only feasible method for viable hatchery production of P. maximus larvae in Norway.