Isolation of Flavobacterium branchiophilum from Rainbow Trout (Oncorhyncus mykiss) with Bacterial Gill Disease in Tabriz, Iran

Flavobacterium branchiophilum a causative agent of Bacterial Gill Disease (BGD) is a filamentous gram-negative bacteria which produce yellow round colonies in cytophaga agar medium. The outbreak of disease were reported from different part of world. In this study we examined 75 fish sample from farms with a recirculating aquaculture system (n=25), pools with a well water source farms (n=25) and farms with river water supplies (n=25) using cytophaga agar medium for colonies isolation and Gram staining, catalase, oxidase, TSI, SIM, urea, citrate Simon and fermentation tests for identification of colonies. The result shown that 25 samples were infected with Flavobacterium branchiophilum. From the 25 cases, 12 were related to the recirculating aquaculture system, 7 to the fish related the river water and 6 to the fish related to well water farms. There is no significance difference between different method of fish culturing was observed (P>0.05). By regarding to our result environmental, management factors and Stressful conditions like crowding, low dissolved oxygen, high ammonia and accumulation may influence the development of BGD in fish farming units.