Variations in water quality at cage culture sites in Batang Ai reservoir, Sarawak, Malaysia

Abstract

Since its impoundment in 1985, the Batang Ai Reservoir has been utilized for cage culture activities. A few sites in the reservoir have been used for cage culture and one site has been abandoned. This study was carried out in October 2013 during the rainy season to document the water quality at three existing aquaculture sites, one abandoned site, and one station further away from cage cultures activities. Results showed DO concentration at sub-surface ranged from 6.93 to 7.81 mg/L; however at 10 m, the range was 0.32 -2.25 mg/L which was not suitable for fish survival. At aquaculture sites, the highest BOD5 occurred either at sub-surface or 10 m depth of the aquaculture stations and the smallest aquaculture site showed the lowest BOD5. BOD5 at the new aquaculture site fall in Class III. Aquaculture site that has been abandoned for less than a year still showed the lowest DO at 10 m and 20 m. This study showed that the low DO values at depth of 10 m and deeper could cause problem to aquaculture activities in the event of turnover. Cage culture activities at Batang Ai Reservoir had impacted the water quality at the cage culture sites. Hence, monitoring of water quality in the reservoir needs to be carried out in order to determine the impact of aquaculture in different seasons and weather conditions as well as in the case of site abandonment.