Mass tilapia (Oreochromis mossambicus) mortality in floating net cages at Batur Lake, Bangli Regency, Bali Province: a case report

The mass death of tilapia (Oreochromis mossambicus) is the cause of the outbreak of mass death of cultured fish in floating net cages in Batur Lake, Bangli, Bali. The data were collected employing a field survey as material for formulating countermeasures. The sampling area is the Batur Lake, Bangli area, the center for tilapia cultivation in Bali Province. The results of our field investigation show that the upwelling phenomenon caused the cause of the mass death that occurred. The incident happened at the beginning of August, which began with changes in water temperature and wind direction (wind-driven motion). Changes in water temperature cause a mass of nutrient-rich water to move to the lake's surface, thereby reducing dissolved oxygen (DO) levels, which are contained in the water. The high stocking density and accumulation of nutrients from agricultural and anthropogenic activities are the main factors for this outbreak. With this outbreak of mass mortality of cultured fish, the government and relevant authorities are expected to manage the health of the aquaculture environment wisely and issue circulars regarding this case, especially in the center of tilapia cultivation in Batur Lake.