Optimal conditions for artificial fertilization, embryonic development, and larval growth of the purple clam Saxidomus purpuratus in the southern coast of Korea.

Abstract

Laboratory experiments were conducted to obtain the basic information on culture conditions for the larvae of the purple clam Saxidomus purpuratus, one of important clam resources in the southern coast of Korea. This study was focused on (1) the success in fertilization and development from artificial fertilization according to the different months of a year, (2) the viability of sperms after exposure to seawater, (3) and the effects of temperature, salinity, and food organism on the survival and growth of larvae. High fertilization rate of gametes obtained from dissecting gonads was obtained at all months if clams were kept in room temperature. But high successful development occurred only during May-July. Developmental success seemed to be related to the egg quality at the fertilization time. Developmental times for 2-cell, 4-cell, 8-cell, blastula, trochophore, and veliger at 20℃ were 1.5, 2, 4, 18, 24, and 32 hours, respectively. Sperms could survive for up to 8 hours. However, actively swimming sperms could be found within 1 hour after exposure to seawater. Thus sperm should be used for fertilization as soon as possible when they were exposed to seawater. At high temperature (35℃), all the larvae died within 48 hours. Larval survival decreased when salinity was either lower than 20 psu or higher than 40 psu, and it was nearly 0% when salinity was 10 psu. Optimal temperature and salinity ranges of larvae of S. purpuratus were 20-25℃ and 20-40 psu, respectively. Larvae grew from 111.5 to 235.3 μm during 21 days. Larvae grew faster when mixed algal diets were supplied than single kind of algal diets: the fastest growth was observed when larvae were fed on the mixture of Isochrysis galbana and Nannochloris oculata.