Aquaculture studies of the giant scallop Placopecten magellanicus (Gmelin): conditioning of broodstock and energy requirements of the larvae and juveniles

Abstract

The giant scallop, Placopecten magellanicus, has proven very difficult to rear under laboratory conditions. This study aimed at optimizing the growth and survival of Placopecten magellanicus larvae and juveniles under laboratory or hatchery conditions. -- Broodstock was successfully conditioned with algal diets equivalent to 3-5% of their body weight per day on a dry weight basis. The effect of conditioning was estimated by measuring the protein, lipid and carbohydrate content of the eggs and larvae. Conditioned adults produced gametes with approximately 30% more energy reserves than starved females. Algal diets resulted in the production of eggs with the highest content of protein (26-30 mg per million eggs) and lipid (14-18 mg per million eggs). These equalled or exceeded the protein and lipid levels in the eggs of naturally conditioned females. In all cases, carbohydrate was a minor energy reserve (2-3 mg per million eggs). -- Both protein and lipid are important energy reserves in the larvae of the giant scallop. The larvae utilized 60% of the energy reserves sequestered in the egg during development to the D-shaped veliger stage, 3 days at 15ﾟC, regardless of the total energy content of the eggs. -- When the larvae were fed an appropriate diet, (Isochrysis galbana, Chaetoceros calcitrans and Thalassiosira pseudonana) the larvae which had higher energy reserves in the eggs exhibited greater rates of growth and accumulation of energy reserves over the first four weeks of pelagic life. -- The effect of algal cell concentration and body size on filtration rates was studied using a static system. Juveniles ranged from 5 mg to 400 mg in tissue dry weight and the concentration of Isochrysis galbana was varied from 5x10³ to 25x10³ cells/ml. At the highest cell concentration test the smallest juveniles ingested 10% of their body weight per day and the largest individuals ingested approximately 5% of their body weight per day. Comparisons with other species indicate that this ration is sufficient for both maintenance and growth.