Impacts of Aquaculture at Different Depths and Distances from Cage Culture Sites in Batang Ai Hydroelectric Dam Reservoir, Sarawak, Malaysia

Aquaculture is increasingly important world-wide as landings from natural captured fisheries is unable to meet the demand for fish. The Batang Ai Hydroelectric Dam Reservoir, located in Sarawak, Malaysia, has been an aquaculture site for the last 18 years. However, little information is available on the impact of aquaculture on the water quality of the Batang Ai reservoir. Therefore, the objective of this study was to evaluate the impact of cage culture activities on the water quality at different distances and depths from the culture site. Four sampling stations were selected where three were at cage culture sites and one control site. Samplings were conducted at 0 m, 20 m and 100 m distance from the culture site and at three depths; subsurface, 10 m and 20 m. Results show that temperature ranged from 25.2-32.2°C and were in decreasing trend as depth increased. DO ranged from 0.26-8.45 mg/l and at 20 m depth it was significantly lower than other depths. Water clarity decreased as it gets nearer the cage culture sites. TSS ranged from 1.5-9.1 mg/l and were significantly higher at 20 m depth than at subsurface. Conductivity ranged from 33 μS/cm 89 μS/cm and was significantly higher at 20 m depth. At that depth, conductivity values at all cage culture stations were higher than the control station. Furthermore, BOD ranged from 6.80-13.86 mg/l. BOD , nitrate-nitrogen, nitrite-nitrogen and ammoniacal5 5 nitrogen were also higher at cage culture stations when compared with the control. Chlorophyll-a concentrations at 0 m from cage culture stations were higher than the control station. Therefore, proper management of aquaculture activities is required in order to ensure long term sustainability of cage culture at Batang Ai Reservoir.