INDUCED SPAWNING OF THE BLOOD COCKLE Anadara granosa IN HATCHERY

Induced spawning of the blood cockle, Anadara granosa in the hatchery using temperature differences of 5-6ᵒC was successfully obtained in November 2016. The objective of this project is to investigate the technique of induced spawning on Malaysian blood cockle in hatchery and its potential application at spawning ground in Kapar, Selangor. A total of 3.0kg cockle broodstock from Sabak Bernam, Selangor (same broodstock source placed at Kapar) were procured and brought back to hatchery for spawning. Broodstock average size (n=31:range from 32mm-43mm) were 36.4±7.4mm in body length, 28.3±2.2mm in body width, 26.6±2.2mm in body height and 17.5±4.1g of body weight.

Prior to spawning, maturity study was done to examine the readiness of the broodstock for spawning. The result shows that sex ratio was 29% female and 61% male while 6% unknown due to the effect of total releasing gametes or spent stage. Gonad maturity examination showed that 90% of the gonad were at stage II (Ripe) and 4% at stage III (Release). All these biological assessments showed that the broodstocks were very ripe and ready for induced spawning. With these results, a breeding attempt was done on 22^nd Nov 2016 at 2.00pm using 5-6ᵒC differences of sea water temperature i.e. triggering with warm seawater of 34-35ᵒC for a period of 2-3 hours in the spawning tank (normal seawater temperature in the broodstock tank was 28-29ᵒC) and then the broodstock were put to rest by reverting to its normal temperature via feeding algae for up to 7 hours and all these processes were repeated. The matured broodstock responded to the stimulation process at 12.00 noon on 23^rd Nov 2016 producing a total of 10 million eggs with the size of 53.3±4.0µm and metamorphosed the next day into straight hinged larvae sized 88.5±5.3µm in body length and 67.8±4.5µm in body width respectively with hatching rate of 50%  producing up to 5 million straight hinged larvae. A control experiment was also done without a temperature shock and no spawning was observed.

This successfull induced spawning in the hatchery suggested that it may be applied to the cockle spawning ground in Kapar, Selangor which experienced high temperature seawater discharge from electric power plant i.e. Kapar Energy Venture (KEV). The induced spawning shall occur during the Great Diurnal Tide (GT) and Lowest Astronomical Tide (LAT), where the temperature shocks on cockle happen during low tides. Through this studies all related information on broodstock conditioning, breeding methodology and life cycle of the cockle larvae were recorded to refine and understand of the biological needs during their life cycle stage and also to relate these information with their spawning ground at Kapar, Selangor.