Disease Problems Affecting Fish in Tropical Environments

Abstract

ABSTRACT Aquaculture produce in Asian countries contributes a major share to total global fish production. However, disease due to biotic and abiotic factors results in considerable losses to the industry. The most frequently encountered bacterial agents associated with fish diseases in tropical environments are Vibrio sp. in marine and brackish-water systems and motile aeromonads in freshwater systems. Virulence mechanisms of these bacterial species have been widely studied. Though a few viral agents such as rhabdovirus, reo-like virus, infectious pancreatic necrosis virus, picornavirus, and irido-like virus have been recorded in different parts of Asia, such reports are scanty. Among fungal pathogens, Aphanomyces invaderis is the most virulent and has been reported to be associated with epizootic ulcerative syndrome. Other fungal agents such as Achlya sp. and Saprolegnia sp. have been recorded in various disease conditions. In addition to various conventional microbiological and serological methods, nucleic acid-based methods are being widely adopted for diagnosis of different fish diseases. Few successful vaccines have been developed to protect against disease conditions, and some of the better known ones are against vibriosis and furunculosis. Many other vaccines are still in the experimental stages. Early diagnosis of disease and development of successful vaccines are important for the future development of aquaculture.