Results

Benzalkonium is a cationic surfactant, and carries clear warnings that aquatic organisms can be harmed by this substance. Benzalkoniumm is widely used in the presence of fish in aquaculture, where it is used to prevents parasitic colonisation of fish and shrimp stocks, and to control algal growth.

The increase in aquaculture production is coupled with an increase in disease outbreaks and to control diseases especially caused by bacteria, antibiotics are being used indiscriminately. The resultant setbacks have focused the attention on the use of immunostimulants in aquaculture practice to withstand the pathogens. To avoid the use of antibiotics, attempts were made to study the immunomodulatory effect of Benzalkonium Chloride (BKC) in Clarias batrachus. BKC is a quaternary ammonium compound that can modify non-specific and specific responses and can be used as an immunomodulator in fishes. To determine the immunomodulatory effect and optimum doses to be applied as injection, bath and feed, the catfish Clarias batrachus was used as an animal model. BKC was applied in three forms, i.e. injection at the rate of 5, 50 and 500 g/kg of the fish weight, bath at 2 and 3 ppm levels for 1 hour and incorporated in feed @ of 1,5 and 50 mg per kilogram dry weight of feed. White blood cells counts, differential counts, phagocytosis, agglutination assay, NBT assay and serum bacterial activity of the fish was performed for assessing the
changes in specific and non-specific responses to BKC. The BKC treated fishes showed increased nonspecific and specific responses in comparison to untreated control. The fishes treated with immunostimulant and later challenged with a virulent strain of Aeromonas hydrophila, showed delayed and lower mortality than the untreated controls. The present study suggests that BKC can be used as an immunostimulant and can be administered in different forms, like injection, 3 ppm as bath and 50mg/kg dry weight of BKC in feed.