Hatchery cultivation of king scallop ( Pecten maximus) spat with cultured and bloomed algal diets

Abstract

Growth rates of small (2–15 mm shell length) hatchery-reared king scallop ( Pecten maximus L.) spat were estimated by computer analysis of video images taken of the scallops held in petri dishes containing seawater. This technique reduced the amount of handling and minimised any effect stress due to handling might have had on growth. Experimental diets consisting of algae from both intensive hatchery cultures and from outdoor bloom tanks were fed to the scallop spat. For all diets, growth rate (as increase in shell length) increased linearly with a logarithmic increase in initial shell length. Scallops thus characteristically showed a growth pattern whereby dry weight-specific growth rate increased rapidly with increasing shell size to a maximum at 4–5 mm shell length (2.6–5.0 mg dry weight). This weight-specific growth rate then showed a gradual decrease with a further increase in shell size. For the algal diets consisting of single species that had been cultured intensively, nutritional value was in the order Pavlova lutheri (Droop) Green> Chaetoceros calcitrans (Paulsen) Takano> Rhinomonas reticulata var. reticulata Novarino>T-ISO ( Isochrysis sp.)> Tetraselmis suecica (Kylin) Butcher. A mixture of the first two of these species gave significantly faster growth rates than any other combination of species tested. Growth rates of scallop spat fed bloomed seawater at rations of 0.33–1.0 g (organic weight of algae) g −1 (live weight of spat) week −1 were similar to those fed an intensively cultured algal diet of high nutritional value. There was some evidence that the spat were less efficient at filtering smaller (2–5 μm) algae cells.