Chalerm Wanman, Thanawut Klowkliang, and Kitjakarn Supamattaya

pp. 291 - 305

Abstract

Streptococcus sp. isolated from infected seabass (Lates calcarifer) can grow on medium at pH 9.6 and
salinity 0 ppt. The lethal dose where the mortality is 50 percent (LD₅₀) was 1.937×10³ CFU/ml after 14 days.
Diseased fish showed dark body coloration, erratic swimming, exophthalmia, dropsy, pale liver, splenomegaly
and hemorrhage in the brain. Blood parameters i.e. haematocrit, haemoglobin, plasma protein and red
blood cell of infected fish were decreased, while white blood cells were increased. Histopathological changes
in diseased seabass were necrosis, vacuolization and granuloma of the liver, increased number of melanomacrophage in liver and spleen, shrinkage of glomerulus in kidneys, inflammation and necrosis of the spleen
and heart, hyperplasia and telangiectasis of the gill, while vacuolization and capsulation of the exophthalmic
eyes were observed.