The role of isolation of different streptococcus species in fish pathological lesions

This study investigates the presence of Streptococcus species in Nile tilapia (Oreochromis niloticus) and mullet (Mugil cephalus) collected from aquaculture showing clinical signs of bacterial infection. A total of 25 fish were examined for both external and internal abnormalities such as exophthalmia, skin hemorrhages, fin rot, ocular opacity, and erratic swimming behavior. Samples were aseptically taken from the kidneys, gills, eyes, and heart and cultured on blood agar to evaluate colony morphology and hemolytic patterns. Colonies displaying typical characteristics were subjected to Gram staining and a series of biochemical tests to identify bacterial species. Microscopy revealed Gram-positive cocci in chains or pairs, consistent with the morphology of streptococci and enterococci. The results confirmed the presence of Streptococcus agalactiae and Enterococcus faecalis in the collected samples. This study highlights the concurrent occurrence of these pathogens in farmed fish and emphasizes the importance of accurate diagnosis and strengthened biosecurity measures to minimize bacterial disease outbreaks in aquaculture operations