The Early Development of the Short-Necked Clam, Paphia undulata (Born 1778) (Mollusca, Pelecypoda: Veneridae) in the Laboratory

The population of Paphia undulata in Negros Occidental waters continues to decline due to unregulated harvesting because of the increasing demand for this resource. One potential effort to mitigate this problem is reseeding or stock enhancement of the natural population. For these efforts to be effective however, successful laboratory rearing and breeding of this species is a prerequisite. Thus, this study was conducted to describe the embryonic and larval development of P. undulata to provide information on laboratory larval rearing. Broodstock were collected during the natural spawning peak from Hinigaran, Negros Occidental and were maintained in a static system with a mean salinity and temperature of 36 ppt. and 26.7 OC, respectively and were fed with Isochrysis galbana, Chaetoceros calcitrans, and Tetraselmis tetrahele. Fertilized eggs started to divide 30 minutes after fertilization. Ciliated swimming blastulas were observed after 1.5 hours with an average shell length (SL) of 40 μm. These further developed into trocophore larvae (average SL 60μm) after 7 hours and into D-veliger (average SL 80 μm) after 12 hours. Fully developed D-larvae (average SL 90 μm) were attained after 17 hours. Larvae with completely developed umbo were observed on day 9 with an average SL of 140 μm. On day 13, larvae (average SL 220 μm) started to settle and metamorphose. Spontaneous spawning was observed during the peak of reproductive activities of P. undulata showing that collection of broodstock must be conducted during the peak of reproductive season to ensure successful spawning and production of viable gametes under laboratory conditions. Further experiments should be conducted to determine optimum conditions to improve survival rates of the larvae during settlement. The results corroborate other studies and help explain the derived information on the species' population and reproductive biology.