Casualty Agent (Yersiniosis) Detection in Reared Rainbow Trout (Oncorhynchus mykiss) in Kohgiluyeh-Va-Boyerahmad Province in Iran

Abstract

From the June to the August 2013, Casualty happened in fish of some ponds of a farm in an area of Kohgiloye-&-BoyerAhmad province. It is a province in southwest of Iran. Three ponds from eight showed more mortality, they have 5 to 20 dead fish every day for 45 days. Afflicted fish have dark body they swimming near surface or at the bottom of the pond and swam unmatched by the flock. Some fish showed hemorrhages around eye and within the oral cavity and exophthalmia occasionally. 45 moribund rainbow trout sampled for dissection and bacteriological examination. Kidney, liver and spleen of moribund fish examined for the detection and identification of bacteria causative agent of disease in rainbow trout. They cultivated aseptically on different media (Blood Agar, Tryptic soy Agar, TCBS Agar and MacConkey Agar).All fish have been infected and suffered septicemia. A type of gram's negative bacterium was responsible of infection and mix infection didn't confirmed. The bacteria were able to growth on MacConkey agar. Detection had done based on clinical finding biochemical tests and staining. Based on it, the bacteria was a bacterium very similar with Yersinia ruckeri which induced infection. Identification continued by PCR method, therefore above result confirmed. Frequency of infectious fish estimated at least 0.375 percent. Application of enrofloxacine for 7 days reduced mortality but could not eradicate the infection so antibiotic therapy repeated 7 days more to eradication.