Abstract
Three thousand topshells, Batillus cmrnutus, artificially igcubated and cultured in tank until about 20mm in shell height, were released to four rocky and stone areas with a depth of 0-0.5m, 0.5-1.5m, 1.5-2.3m and 2.3-4.0m respectively, in the western Wakasa Bay, on the 28th of May, 1984. The growth and survival rates of the topshells after releasing decreased with the increase of depth. In the azea with a depth, shallower than 0.5m, the topshells grew up to 37mm in mean shell height and 89% shells survived for 136 days. The highest growth rate (6.0mm per month) obtained between August and October. On the other hand, in the deeper area with a depth of 2.3-4.0m the shells grew up to 27mm and only 2.4% shells survived for 136 days. After releasing, the topshell moved only short distance. For example in the area shallower than 0.5m, the shell diffused horizontally up to 12m from the released point in 136 days, especially 55% shells aggre-gated in the neighbouring area of released point (up to 4m from released point). The above results, suggest that the area with 0-0.5m depth is satisfactory for growth and survival of young topshell, compared with the area of more than 0.5m depth.
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