SEA RANCHING OF Holothuria atra: STOCKING DENSITY AND TIME

Strong market demand, uncontrolled exploitation and/or the inadequate fisheries resource management have caused the overexploitation of sea cucumbers. Hence, sea ranching is suggested as an intervention to overcome, if not minimize, this problem. Since stocking density is the most important consideration in sea cucumber rearing, this study is aimed at discovering the best stocking density for the ranching of Holothuria atra. H. atra individuals were taken from the Panjang Island, Jepara waters and reared in cages at the bottom of Teluk Awur waters, Jepara with a density of 30, 20, or 10 individuals per cage measuring 2 × 2 × 1.8 m (with bottom area of 4 m2). The stocking of H. atra was carried out three times, starting from the time of cage installation, then at the second, and finally at the third months after installation. Characteristics of the bottom sediment (i.e., chlorophyll a, b, phaeophytin, and total carotene) of the sea cucumber habitat and water quality in the cages were also measured monthly. This study showed that the growth of H. atra fluctuated. The low stocking density yielded a higher weight gain per individual than the high stocking density. The highest weight gain was observed at the stocking density of 10 individuals/cage in the second stocking month. The highest survival rate was recorded at stocking density of 30 individuals/cage (93%) in the third stocking month, considering that these sea cucumbers were only reared for three months. The highest mortality occurred at stocking density of 20 individuals/cage. Low survival rate of 45% occurred at the first stocking time or after the fifth month of rearing. Fission was observed among H. atra reared in the cages, resulting in smaller organisms. Among the water quality parameters, the concentration of chlorophyll a, b, phaeophytin, and carotene in the sediment fluctuated with the rearing duration due to the feeding and bioturbation of sea cucumbers. The results of this study suggested that low stocking density of H. atra during the second stocking month yielded a higher growth rate.