Spawning induction and fertilisation in the doughboy scallop Chlamys (Mimachlamys) asperrima

To facilitate hatchery production of the doughboy scallop, Chlamys (Mimachlamys) asperrima (Lamarck) several factors involved in the spawning and early larval development of the scallop were investigated. A comparison of temperature induction and serotonin spawning techniques found serotonin to be a rapid effective inducer of spawning. Both intragonadal (IG) and intramuscular injection of 0.05 ml of 10^-3 M serotonin solution induced egg release after approximately 30 min, however, IG injections resulted in greater numbers of eggs released. Sperm release occurred approximately 20 min after 0.05 ml of 10^-2 or 10^-3 M serotonin solution was injected IG. Temperature induced spawning produced greater egg release than serotonin although fewer scallops spawned and the time taken to induce egg release markedly increased. For maximum egg yields a combination of temperature induction and serotonin injection techniques are suggested. The percentage yield of D veligers from eggs spawned using temperature or serotonin induction did not differ significantly. Following spawning, the combined effects of gamete storage time and temperature on fertilisation were evaluated, as were the effects of various sperm to egg ratios and egg stocking densities during incubation on the yield of D veligers. On the basis of the results, fertilisation of C. asperrima eggs should be conducted within l h of release, when sperm should be added until approximately one sperm is visible at the periphery of each egg. Reductions in storage temperature for sperm, in the range 15 to 24 °C, prolonged the period sperm remained motile and maintained higher fertilisation rate. Reducing the storage temperature for eggs had no effect upon percentage fertilisation when tested 4 h after release. When fertilised, C. asperrima eggs can be incubated at densities of up to 50-100 ml^-1 without affecting the yield of D veligers.