Hybrid catfish farming has developed very successfully in Thailand over the last 10 years. Farmers, however, are still encountering disease problems and as a result, face economic loss. Some disease problems are associated with inadequate farm managment practices. This study was carried out to investigate the presence of bacteria in macrophage cells isolated from hybrid catfish cultured in different environmental conditions. Results from farm investigations showed that the percentage of macrophages containing intracellular bacteria was related to particular water quality paramers.
Experimental trials were conducted using high stocking density as stressor and bath challenge with pathogenic Aeromonas hydrophila. The results showed that the fish kept in high density and bath challenged with bacteria had a higher percentage of macrophages containing bacteria than those kept under normal conditions. The presence of bacterial loading in macrophage cells is therefore considered to be an indication of the health of the fish.