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Background: Lactococcus garvieae is one of the most important risk factors in the rainbow trout culture. Therefore, the purpose of this study was to identify and detect strains isolated from rainbow trout suspected of having Lactococcus garvieae using biochemical characteristics and PCR and determination of the degree of severity of isolated strains. Methods: In this study, the cause of lactococcosis in selected rainbow trout farms in Kohkilooieh and Boyerahmad province was assayed. Gram-positive and catalase-negative bacterial isolates were first obtained from selected trout fish farms using conventional biochemical tests and PCR assay. The 10-day LD 50 method (concentration causing 50% mortality in 10 days) was used to determine the severity of the isolated bacteria. Results: One bacterial isolate was detected from all sampled fish which confirmed as Lactococcus garvieae using a specific PCR assay based on the 16S rDNA gene by producing a single band of 1107 bp. Analysis of the rate of mortality showed that the 10-day LD 50 was 4.6 × 10 5 CFU/fish. The results of this study showed that isolated bacteria had high severity for rainbow trout. The presence of bacteria in internal organs of suspected fish showed a severe systemic infection in challenged fish. Antibiogram assay also indicated that the isolated Lactococcus garvieae were resistant to some mostly used antibiotics in rainbow trout. Conclusions: According to current research, it can be concluded that the condition of lactococcosis in the studied area is not suitable, and despite the presence of disease, there is no proper action to control and prevent the disease. Unfortunately, isolated bacteria from the studied area have a very high severity compared to bacteria isolated from other regions of the country or other countries. Therefore, further investigation is needed to determine the cause of this difference and possibly in the design of the vaccine.

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This study aimed to investigate the effects of rosemary leaf extract (Rosmarinus officinalis L.) on growth, haematological parameters, immunological profile and body composition in common carp (20.35 ± 0.37 g). The fish (n = 240) were fed with 0.0%, 0.25%, 0.5% and 1% of rosemary extract in 12 aquaria (300 L) with three replicates (each with 30 fish) for 60 days. At the end of the trial, final weight, WG, SGR, FCR and CF levels were significantly higher in a dose-dependent manner in the groups fed the diet containing rosemary extract compared with the control group. Moreover, the results of measured trial indices showed a significant increase in a dose-dependent manner in WBC and RBC counts, haemoglobin, haematocrit, lysozyme, complement, respiratory burst, total protein, albumin and glucose in the fish fed the diet containing rosemary extracts compared with the control group. The contents of cholesterol, triglyceride and LDL were significantly decreased in a dose-dependent manner and HDL level significantly increased in the groups fed diets containing rosemary extract.The findings of this research suggest that adding rosemary extract, especially 1%, to the food regime could positively change the growth parameters, haematological and immunological profiles of Cyprinus carpio.

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