Detection of Streptococcosis among freshwater fish, Nile tilapia (O. niloticus) and marine fish, grey mullet (M. cephalus) was confirmed. The disease of both fishes is characterized by hemorrhagic areas on the body surface, particularly around the mouth and operculum. Corneal opacity with congested swelling around the eye ball was a common nature of the disease in O. niloticus, while, abdominal distention usually observed in M. cephalus. Internally, O. niloticus exhibited splenomegaly while in M. cephalus, the abdominal cavity filled with yellowish fluid, the stomach and intestine contained yellow to yellowish green gelatinous material and pale colored liver. The bacteriological examinations revealed isolation of Streptococcal species linked with but not identical to Streptococcus faecalis and Streptococcus faecium bacterial isolates able to produce the disease and cause 100% deaths when the fishes were injured prior to dipping in the bacterial suspension. No deaths occurred among fishes in of orally administered the bacterial suspension.