Issues Related to Blood Cockle Anadara granosa Mortality in West Coast of Peninsular Malaysia.  

The mudflats of the west coast of Peninsular Malaysia are very productive, producing 72,000 tonnes of marketable cockles and 11,000tonnes of cockle seeds (Mohd. Mazlan, 2000). Based on the Fisheries Annual Statistic Report 2000, issued by the Department of Fisheries Malaysia, the total production of cockle landings in Selangor was 6,922 mt utilizing 654 ha farming area with a production rate of 11 mt/ha. Meanwhile, in the 2011 report, the total production of cockle landings had increased remarkably to 26,505 mt with further expansion of 5,593 ha of cockle farming area. It shows an increasing number of productions and area of cockle's farming. However, the production rates for 2011 had declined to 4.7 mt/ha. The declining of cockle's production rate was due to several factors. Poor water quality with special reference to ammonia, increased stocking density and invasion from the 'siput rantai" (clam) were some of the factors mentioned to explain the losses. This paper presents water quality data and sediment texture from several locations sampled over 2014- 2015 experiencing cockle mortality in an attempt to elucidate contributing factors to the aquaculture problem. Condition index values of the cockles over the growth period as well as proximate analysis data were determined as a basis of comparison between locations sampled.

Results indicate poor water quality especially dissolved oxygen and ammoniacal nitrogen during neap tide could be a contributing factor to cockle mortality. Condition index values reflect poor growth in cockles from areas experiencing poor water quality.

Laboratory bioassays carried out to determine LC 50 and EC 50 values for ammonia in solution exposures are ongoing.  Preliminary findings show reduced feeding by cockles exposed to sub-lethal concentrations.