Research on Molluscs and Seaweeds

This paper reviews the progress of mollusc and seaweed research at SEAFDEC/ AQD from 1995 to 1999. Because of the pressing need for seedstocks for stocking, research on the donkey’s ear abalone, Haliotis asinina focused on the development of seed production and culture techniques. To improve the spawning performance and egg/larvae production of captive broodstock studies on reproductive biology, management of broodstock and development of diet were conducted. Studies to refine techniques for post-larval settlement and metamorphosis and development of nursery rearing techniques were carried out to increase production of abalone juveniles. An artificial diet has been developed to enhance growth rates of juveniles during nursery as well as grow-out. However, since long-term use of artificial feeds did not favor the growth and survival of abalone during grow-out culture in tanks due to difficulties in maintaining water quality, sequential feeding with artificial diets and then seaweed Gracilariopsis bailinae seemed more practical. Broodstock development and seed production were the major research areas for the window-pane oyster Placuna placenta. Gonad development was enhanced by feeding a mixture of high densities of Isochrysis galbana and Tetraselmis tetrahele at a 3:1 ratio. P. placenta larvae reared with Isochrysis as feed showed the best growth and survival. Settling stage was reached after 14 days of rearing. A salinity of 34 ppt was optimal for larval survival. Poor growth and survival of larvae was observed at low (10 ppt) and high salinity (40 ppt) levels. Re-stocking of immature adults and juveniles was conducted in a depleted coastal bed to evaluate the potentials for recruitment of the window-pane oyster. After 91 days, a survival rate of 51% was observed among immature adults. No juveniles survived after re­ stocking.