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. Gametes obtained from dissecting gonads showed high fertilization rate at all months, but developmental success was higher only in May-July. Developmental success seemed to be related to the quality of eggs at the time of fertilization. Developmental times for 2-cell, 4-cell, 8-cell, blastula, trochophore larva, and veliger larva at 20℃ were 1.5, 2, 4, 18, 24, and 32 hr, respectively. Sperms could survive for more than 8 hr; however, actively swimming sperms could be found within 1 hr after exposure to seawater. It is recommended that sperm should be used for fertilization as soon as possible when they are exposed to seawater. At temperature of 35℃, all the larvae died within 48 hr. Larval survival decreased when salinity was either lower than 20 psu or higher than 40 psu, and was 0% when salinity was 10 psu. Optimal range of temperature and salinity for rearing 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 fed with mixed diets grew faster than unialgal diets. The fastest growth was observed when larvae were fed on the mixture of Isochrysis galbana and Nannochloris oculata.