The Parasites of Etroplus suratensis (Bloch) (Pisces: Cichlidae) and Their Effects on Aquaculture Management
N. NILAKARAWASAM and C SOMMERVILLE
The parasite fauna of the cichlid Etroplus suratensis (Bloch), a typical estuarine fish capable of withstanding salinities ranging from freshwater to brakish and considered as a promising candidate for aquaculture in the range, was investigated with a view of understanding their importance in aquaculture. The study was carried out in Koggala lagoon and Udawalawa reservoir in Sri Lanka. Parasites were identified and their importance in aquaculture was estimated by] considering their ability to appear in fresh and brackish water systems, their population levels, the effects of environmental parameters on population fluctuations, the possibility of building up of population levels and their pathological effects.
A considerable number of parasites are newly recorded for E. suratensis. Most of the digeneans, all nematodes, and all crustaceans are new records of Sri Lanka. Of ectoparasites, Ichthyobodo sp. and all monogeneans were shown to be tolerant for wide range of salinity. Most of the parasites with indirect Iife cycles were unable to survive in both habitats, probably due to the absence of suitable intermediate or final hosts. Drastic fluctuations in abundance levels of parasites were not observed seasonally. Monsoon rain was the main factor which brought about the changes and a slight fall in temperature appeared to influence cercarial release of ectoparasites. Icthyopthirius sp., Icthyobodo sp. and gill monogeneans seemed to thrive in freshwater systems whilst gill monogeneans and copepods were abundant in brackishwater. However, the possibility of having high infection levels with other parasites cannot be eliminated in conditions which favour high densities of intermediate host. Some parasites were considerably pathogenic, whilst the importance of others cannot be eliminated at high infection levels.