Survey on streptococcosis in selected farms of rainbow trout (Oncorhynchus mykiss) in Yasuj province

Streptococcosis is one of the most critical and economically damaging diseases in the aquaculture industry, especially in rainbow trout, and it causes much damage to this industry annually. On the other hand, this disease is most common among humans and fish, leading to disease among consumers of infected fish. To survey the incidence and etiology of rainbow trout suspected of streptococcosis, 50 samples of alive trout which had symptoms similar to streptococcosis were captured from selected farms in Yasuj province. After the autopsy, bacterial sampling of the kidney, liver, and brain was done on a Blood Agar medium. Sampling was done near the flame and with sterilized instruments. Samples were taken to the laboratory of the veterinary school of Islamic Azad University, Kazerun branch, and kept in an incubator for 72 hours at 25 degrees centigrade. Then, gram-negative samples were omitted by the Gram-stain technique and catalase tests, and then complementary biochemical tests were performed after recultivating the samples. The results showed isolated bacteria, including Streptococcus iniae and Lactococcus garvieae. The incidence of infected rainbow trout with a clinical sign of S. iniae and L. garvieae was 68% and 25%, respectively. Infection was not isolated from 7%. Isolation of S. iniae and L. garvieae from kidney, brain, spleen, and liver was 60%, 65%, 58%, 92%, and 26%, 36%, 32%, and 6%, respectively.