SPAWNING INDUCTION AND FERTILIZATION IN THE DOUGHBOY SCALLOP CHLAMYS (MIMACHLAMYS) ASPERRIMA

To facilitate hatchery production of the doughboy scallop, Chlamys (Mi machlamys) asperrima (Lamarck) several factors involved in the spawnin g and early larval development of the scallop were investigated. A com parison of temperature induction and serotonin spawning techniques fou nd serotonin to be a rapid effective inducer of spawning. Both intrago nadal (IG) and intramuscular injection of 0.05 ml of 10(-3) M serotoni n solution induced egg release after approximately 30 min, however, IG injections resulted in greater numbers of eggs released, Sperm releas e occurred approximately 20 min after 0.05 mt of 10(-2) or 10(-3) M se rotonin solution was injected IG, Temperature induced spawning produce d greater egg release than serotonin although fewer scallops spawned a nd the time taken to induce egg release markedly increased. For maximu m egg yields a combination of temperature induction and serotonin inje ction techniques are suggested, The percentage yield of D veligers fro m eggs spawned using temperature or serotonin induction did not differ significantly, Following spawning, the combined effects of gamete sto rage time and temperature on fertilisation were evaluated, as were the effects of various sperm to egg ratios and egg stocking densities dur ing incubation on the yield of D veligers, On the basis of the results , fertilisation of C. asperrima eggs should be conducted within 1 h of release, when sperm should be added until approximately one sperm is visible at the periphery of each egg, Reductions in storage temperatur e for sperm, in the range 15 to 24 degrees C, prolonged the period spe rm remained motile and maintained higher fertilisation rate. Reducing the storage temperature for eggs had no effect upon percentage fertili sation when tested 4 h after release. When fertilised, C. asperrima eg gs can be incubated at densities of up to 50-100 ml(-1) without affect ing the yield of D veligers.