HISTOPATHOLOGY OF HYBRID TILAPIAS INFECTED WITH A BIOTYPE OF STREPTOCOCCUS-INIAE

A systemic streptococcal disease caused by a biotype of Streptococcus iniae affecting hybrids of Nile tilapia Tilapia nilotica x blue tilapi a T. aurea at a commercial aquaculture facility in central Texas was i nvestigated. Histological analysis revealed a general septicemia with the occurrence of cellular infiltration and numerous cocci in most org an systems. Observations included cellular infiltration of the eye, me ningitis, meningeal granuloma, numerous foci of infection, and massive cellular infiltration in the kidneys; Bacteria were seen in the subca psular capillaries of the liver, and some liver tissue was granulomato us. Splenic sinuses contained numerous cocci, and both epicarditis and myocarditis was observed in the heart tissue of some specimens. Cocci were free in the plasma of infected fish and often phagocytized by ma crophages.