A granulomatous disease in Pejerrey (Odontesthes bonariensis).

TOGO MIYAZAKI; GABRIELA C. LÓPEZ; VIVIANA LOBATO; GUSTAVO E. BERASAIN; LEANDRO A. MIRANDA; GUSTAVO M. SOMOZA

San Carlos de Bariloche

Simposio; VI Simposio Argentino de Ictiologia; 2019

Since 2016, there has been broken out a sub-acute mortality in the pejerrey stock taken from the wild and reared in Junín hatchery. The mortality rate of this wild fish (collected from Gómez Lake, Junín county, Buenos Aires) was significantly higher than the one of the farmed fish group (from Estación Hidrobiológica de Chascomús), though these groups were reared in the same hatchery. Also, the mortality rate is higher between spring and summercompared with other seasons. Diseased fish sometimes showed light hemorrhages on the skin of body surface and occasionally pop eyes. After a naked eye observation on inside organs, some white and hard particles were seen in the kidney, spleen and liver. The histopathological observation showed that these particles were mainly consisted by macrophages, epithelial and fiber cells, so they can be named as granuloma. Occasionally, these granulomas were also found in the heart and testes but never in the gills, intestine, ovary nor in the brain. A bacterial examination trying to isolate the causative agent wasperformed, using different media: nutrient agar, 5% NaCl added nutrient agar, BHI agar, blood BHI agar, Sabouraud agar, cytophaga agar and Ogawa plate, but no colonies were grown from diseased fish samples. Also, a PCR examination with primers covering wide range of Mycobacteria was performed, using DNA extracted from the kidney of diseased fish, but any specific amplicon was appeared. In sum, until now, the causative agent of this disease is unknown.