histopathologic study of rainbow trout (oncorhynchus mykiss) skin and intestine affected with lactococcus garviea

rinbow trout (oncorhynchus mykiss) is an important fish species in aquaculture. the bacterial disease caused the decline in the production of this fish. lactococcus garvieae is one of the most serious infectious agents that caused disease with economical losses in fish farms. streptococosis have signs similar to lactococcosis. therefore the definite diagnosis is sometimes complicated. in the last 5 years, the disease suspected to be streptococosis was epidemic in rainbow trout farms in ilam. in this research, 60 diseased rainbow trout with clinical signs such as erratic swimming and exophthalmia, were collected from rainbow trout farms. for detection the agent of the disease, samples were collected from spleen, kidney and liver of fishes. based on the biochemical tests and multiplex pcr by using three sets of primers designed from 16s rrna, 16s- 23s rrna and (lcto) genes of l. garvieae, s. dysgalactiae and streptococcus iniae, the isolates in this research, produced a single specific fragment bands with a size of 1100 (bp) have shown and characteristics of l. garvieae. some of histopathological that observed was necrosis of epidermal cells and ulcer in the skin and hemorrhage, increase of mucosal cell (goblet cell), infiltration of inflammatory cell in the intestine. in conclusion of the present study confirmed that l. garvieae is the main agent of the epidemic disease in the rainbow farms in ilam use of the m-pcr method.