Spawning, larval development and spat settlement in the Venus clam Gafrarium tumidum (Roding, 1798) from south-east coast of India

Abstract

Induced spawning, larval development and spat settlement of the venus clam Gafrarium tumidum (Roding, 1798) were studied. Brood clams (27.5-32.8 mm dorsoventral measurement / 5.3-15.8 g) collected from the natural bed were conditioned (24.0 -26.0 °C; 33.5-34.5 ppt) and subjected to thermal stimulation for spawning. Fertilised eggs were spherical in shape and measured, on an average 62 μm in diameter. Day one veliger larvae of mean size 91 ± 1.69 μm transformed into umbo stage on day 7 at a size of 149 ± 6.02 μm, pediveliger on day 11 at 180 ± 6.0 μm size developed functional foot which settled on day 13 at a size of 200 ± 6.945 μm. The growth of post-set clams was monitored and described upto 68 days and the growth equation was derived. Few surviving post-set clams transformed into juveniles and radial ribs were observed with naked eye when they were 2.3 mm in 75 days. These clams reached 6.4 mm in 165 days. Metamorphosis and larval growth are compared with that of other bivalve species reported earlier. Further, specific refining of methodology for post-set clam rearing would pave way for their mass seed production for aquaculture purpose.