Shrimp culture industry in Sri Lanka depends mainly on the Chilaw - Mundel - Puttalam estuarine system connected together by the Dutch canal; for its brackish water requirements. The shallow semi-enclosed system with very limited tidal exchange also acts as the receiving body for untreated effluents discharged from farms. All farms are situated along a narrow coastal belt of approximately 120 Km. The farm density increased rapidly during the mid 1990’s increasing the pressure on the environment. Presently it varies from 20ha/lKm of water source to 50ha /lKm of water source. This high density has resulted in close location of farms contamination of water source and self pollution; causing rapid spread of disease. This paper reviews the major epizootics experienced by the shrimp industry in Sri Lanka and the environmental conditions which favoured their spread.
The estuarine system itself has been affected by autopolution from shrimp industry and shows a time series deterioration in water quality, activities. The problem is further aggravated by management practices adopted by farmers with respect to percentage water exchange feeding and release of effluents
Three major epidemics observed in the Sri Lankan shrimp culture history; caused by viral infections. All pathogens had been newly introduced to Sri Lanka by the import of post larvae and broodstock.
The first major epizootic Monodon Baculovirus (MBV) affected during 1989-1991 period,. The environmental factors identified for the rapid spread included high stocking density (>30 pl/m2), high feed input, poor water management and problems related to conversion of acid sulphate soils for shrimp culture.
The second epizootic - white spot virus occurred in 1996 and still continues to damage the production. The rapid spread was triggered by close proximity of farms, suboptimal water quality in ponds, autopolution and feed management.
Third epizootic - yellow head virus appeared in 1998 and affected farms in areas Chilaw and Arachchikattuwa. The water quality of source water and in ponds were suboptimal for shrimp culture with respect to many parameters. Poor management practices and contamination of natural ecosystem aided rapid spread.
The above information shows the deterioration of environmental conditions in culture ponds and estuarine system triggers rapid spread of disease. Environmental management in shrimp culture reducing the strain on the natural eco-system is the only option for sustainability of the industry.