EXPERIMENTAL PATHOLOGY OF STREPTOCOCCUS SP. IN RAINBOW TROUT, ONCHORHYNCUS MYKISS

Experimental pathology of Streptococcus sp. was studied in Rainbow Trout weighing 18- 20 grams each using bath (1.5x103, 1.5x104, 1.5x105, 1.5x106, 1.5x107, 1.5x108 cell/ml for one hour) and intraperitoneal (1.5x103, 1.5x1041.5x105, 1.5x106, 1.5x107, 1.5x108 cell/fish) challenges provided at 18°C. Control groups were included by intraperitoneal injection of fish with sterile phosphate buffered saline (0.5 ml/fish) after anesthetizing fish with clove oil (100 mg/l). Six groups consisting of 12 fish each were used. No morbidity or mortality occurred in bath-immersion groups, while mortality occurred in intraperitoneally injected fish 24 hours post-challenge and reached LDsoat 1.5x108 cell/fish 72 hours post-challenge. The affected fish showed anorexia, darkening of body, exophthalmia, and prolapsed anal abdominal distension. In his to-pathological sections, there were hyperemia and sinusoidal congestion plus necrosis and degeneration of liver hepatocytes. Also, hyperemia in heart tissue, an increase in interstitial tissue plus necrosis of kidney tubular, edema of Bowman capsules together with an increase in melanomacrophage centers of kidney tissues were seen. In addition, congestion of spleen ellipsoids and necrosis of spleen cells were observable. Detachment of basal membrane of secondary lamella with infiltration of inflammatory cells, congestion and edema of menangial layers, hemorrhage in orbital adipose tissue and destruction of eye cornea were also observable.