Why do ‘fish kills’ occur?

Have you been wondering why "fish kills" occur in lakes of volcanic origin?

In the science world, the phenomenon is called lake overturn, said the Philippine Council for Aquatic and Marine Research and Development (PCAMRD).

"Lake overturn takes place in deep inland water bodies like Taal Lake when the cooler mass of water at the surface is forced by winds to displace  the warmer and oxygen-poor water mass at the bottom known as hypolimnion," explained Los Banos-based  PCAMRD headed by Executive Director Rafael D. Guerrero III.

In Taal Lake (Batangas) , overturns commonly happen from December to February with the "cool season" and the strong winds of the northeast monsoon (amihan).  Fish kills have also occured in April and August .

UP Los Banos and DA-Bureau of Fisheries and Aquatic Resources have also fish kills in Taal Lake attributed to wind-induced overturns in 1993 and 2000.

"During such phenomenon, the surface water becomes acidic because of sulfur compounds brought up from the bottom and smells strongly  of ‘asupre’," they said.

Records compiled  by this writer also showed that lake overturns have taken place in such bodies of inland water as Alligator Lake in Los Banos, the lakes in San Pablo City (Laguna), Lake Buhi (Camarines Sur, home to the world’s  smallest commercial fish species  named  ‘sinarapan’ ), and Lake Sebu in South Cotabato.

"Lake overturns cannot be prevented," PCAMRD said.  However, fish growers can minimize losses by reducing farming operations during the cold months and by not overfeeding and overstocking their fish in cages so as not to increase the lake bottom’s organic load. – RAF