Investigation of massive fish kill in Lake Buhi, Camarines Sur, Philippines

Abstract

Lake Buhi is a multi-species fishery resource and known worldwide for being the home of the world s smallest commercial fish (Mistichthys luzonensis). The lake is used for fishery, agriculture, irrigation, hydroelectric power, navigation, and domestic purposes. Any particular use of the lake s resource system will have beneficial or adverse effect to its immediate environment. Man-made intervention such as unregulated fish cages, unsound farming system practices, establishment of control structure for irrigation and the hydroelectric power plant, and improper waste disposal alter the ecosystem. Ecological imbalance has serious consequences for it affects the entire lake. The occurrence of massive fish kill in Lake Buhi is due to depletion of oxygen. Values dropped from 0.05 to 1.0 mg/L, which is lethal to the fish. This is brought about by the upwelling of accumulated organic pollutants from the lake bottom: (detritus and domestic waste, decaying unused feeds, fish excretes accumulated by overstocked tilapia in cages), the proliferation of water hyacinths, and fluctuating water level. These resulted to the formation of ammonia (NH₃), carbon dioxide (CO₂), and hydrogen sulfide (H₂S) that have exceeded the tolerable level for fish life. These factors caused high temperature (29°-30°C), enhanced respiration of aquatic life, and decreased the solubility of oxygen. Likewise, increased bottom sediments (2.3 - 3.0 m) and very low transparency (0.82m) that block the penetration of sunlight and hinder photosynthetic activity in the water were recorded. The inequitable access and use of fishery resource are the major problems that beset the lake. There is a need for sound fishery management and regulatory intervention to help resolve the problems affecting the productivity and stability of the lake s ecosystem.