Background: Persistent mortalities were observed in rainbow trout (Oncorhynchus mykiss) propagation farms around of Hamedan Province in western of Iran in September 2009. Affected fish, with size of 100-150 g., showed lethargy, spiral...
moreBackground: Persistent mortalities were observed in rainbow trout (Oncorhynchus mykiss) propagation farms around of Hamedan Province in western of Iran in September 2009. Affected fish, with size of 100-150 g., showed lethargy, spiral swimming and had dark color, hemorrhages at base fins and vent, anal prolapse, reddening of maxilla and mandibular areas, palate, gill operculum and eyes. Objective: The aim of this study was to control and prevent for eliminating the adverse environmental factors and excessive stresses to reduce the ERMD occurrence. Methods: Environmental parameters measuring revealed low water quality i.e.; pH = 5, high temperature (18-20 o28 C), excess ammonia (NH3 = 0.05 mg/L), dissolved oxygen (O2 = 4-5 mg/L), marginal carbon dioxide (CO2 = 8 mg/L) and H2S gas bubbling. The fish were also subjected to low quality feed, overcrowding, handling stress, and high aquatic plant growth. Twenty five bacteriological samples were collected from the lower intestine, posterior kidney of moribund fish. Samples were cultured on TSB media and Yersinia selective agar. Results: Results revealed the presence of Gram-negative and motile rods which had the expected biochemical characteristics. So the isolated bacterium was confirmed to be Yersinia ruckeri which had a positive agglutination with rabbit anti-K ruckeri serum. Conclusion: For the antibiotic sensitivity test, combination of Sulfamerazine and Oxytetracycline was recommended. Recommendation protocol was issued as control and prevention measures to eliminate the adverse environmental factors and excessive stresses to reduce the disease occurrence.
