Effect of algal cell density, dietary composition, growth phase and macronutrient concentration on growth and survival of giant scallop Placopecten magellanicus (Gmelin, 1791) larvae and spat in a commerical hatchery

Ryan, Catherine Maxine (2000) Effect of algal cell density, dietary composition, growth phase and macronutrient concentration on growth and survival of giant scallop Placopecten magellanicus (Gmelin, 1791) larvae and spat in a commerical hatchery. Masters thesis, Memorial University of Newfoundland.

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Abstract

This study was aimed at optimizing the growth and survival of Placopecten magellanicus larvae and spat by manipulation of the hatchery algal diet with respect to cell density, species composition, phase of harvest, and macronutrient concentration of the algal growth medium. Algae were cultured in a chemostat system in which variations in cell density and growth rate could be controlled. -- This study indicated that an algal cell density of 40 cells/μl resulted in most efficient use of the algal ration. This ration was then fed to spat in subsequent growth trials. Spat were stained with calcein (0.15 g/L seawater) prior to experimentation, for a duration of 72 hours, to introduce fluorescent marker bands which could be used to measure new shell growth in these trials. -- Attempts to improve the standard hatchery diet by the addition of algal species showed that Tetraselmis suecica, Chaetoceros calcitrans and Chroomonas salina were not beneficial as a supplement to a mixed algal diet for Placopecten larvae and spat. -- Scallop larvae were found to grow better when fed logarithmic phase algae or algae cultured under high macronutrient concentration, suggesting a higher requirement for protein during early development. Spat were found to grow better overall when fed stationary phase algae or algae cultured under low macronutrient concentration, which were found to be high in lipid and carbohydrate content important for metamorphosis and postlarval (spat) development. Spat shell growth and total lipid and carbohydrate of the diet were positively correlated. -- The results of the study also indicated that Thalassiosira weissflogii was beneficial in a mixed algal diet for giant scallop spat, and that spat selectively ingest significantly more Thalassiosira weissflogii by volume in comparison to a species of similar cell size, Tetraselmis suecica. -- This study indicates where improvements can be made to traditionally used mixed algal diets fed to larvae and spat in a commercial hatchery giving higher growth and survival prior to transfer to the natural environment at nursery or grow-out sites.

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