Experimental cultivation of Tapes japonica (Deshayes) (Bivalvia: Veneridae) in an artificial upwelling culture system

Abstract

Growth and reproductive characteristics of Tapes japonica (Deshayes) were investigated in a system using artificially upwelled deep-sea water as a culture medium. Three successive generations of Tapes were reared on combinations of three planktonic diatoms: Chaetoceros curvisetus, Bellerochea polymorpha and Thalassiosira pseudonana. Market-size adults (38-mm shell length) were obtained in 13 months from post-set juveniles, and in 10 months from the 5-mm stage. Animal densities at 38 mm were 1 775 and 1 345 clams/m 2 for first and second generations, with survival rates of 64 and 63%, respectively. Ripe gonads were found in adult clams during much of the year. Spawning was readily induced in the hatchery and larvae metamorphosed in 2–3 weeks. Post-set survival rates of 52 and 84.5% were recorded. Juvenile clams (6.5-mm shell length) were fed Chaetoceros and Bellerochea and an unidentified cryptophyte flagellate (designated S-1) in seven different unialgal and mixed-algal diets. The monoculture diets produced slowest growth in clams after 5 weeks, yielding a 7.6-fold average increase in wet meat weight and an average length of 15-mm. The four mixed diets showed better growth as a group, producing a 12.6-fold average increase in wet meat weight. Although variation in growth on the mixed diets was small, the Chaetoceros + S-1 diet gave the best yield for the total number of algal cells provided. Clams fed this mixture averaged 16.7 mm in length and 0.22 g in weight after 5 weeks. This was the best wet meat weight gain of all groups.