Feeding Cockles with Detritus Balls

Abstract

The ‘aging’ of the farm may affect cockle’s growth as it gradually lacks the necessary nutrients and organic matter. In recent years, the annual national cockles’ production has shown a descending trend. Although pollution, stocking density, predation and mangroves destruction may also affect cockles’ growth, this study attempted the prospect of increasing the organic detritus in the cockle’s area as food for the cockles. For this purpose, a laboratory experiment was conducted with the objective to create ‘detritus balls’ suitable to be submerged in the muddy soil and after time releasing decomposed detritus to be consumed by the cockles. Green leaves were buried under the soil for three weeks for decomposition process to take place and later mixed with clay to form several balls .The purpose of the balls is to hold the decomposed leaves and simultaneously heavy enough to be able to submerge in the muddy soil. There were six aquarium tanks in use, each was filled with filtered sea-water, aerated and introduced 30 live cockles. In each of the three tanks, eight detritus balls were placed while the other tanks served as control without the detritus balls. The detritus balls were found to hold intact the decomposed leaves if the leaves composition was between 5-11 % and submerged in mud at about 6 cm. At the end of the observation period, 70 % of the cockles placed together with the detritus balls survived while none survived in the control tanks. The stomach of the surviving cockles was examined and found filled with detritus and other organisms in contrast to the dead cockles. From the results obtained, it indicates that detritus balls can be used in the field to increase organic detritus and thus improve cockles’ growth.

Keywords: detritus balls, mangroves leaves, ammonia, anadara granosa