Experimental infection of in red tilapia ( hybrid) revealed low pathogenicity to cause streptococcosis.

BACKGROUND

Streptococcosis, as a bacterial disease with broad tropism in fish and one of the causes of septicemia. is one of the causative agents of streptococcosis that can be isolated in tilapia.

AIM

This study was undertaken to complete the reporting gap on the pathogenicity profile and clinical symptoms of bacterial infection in red tilapia ( hybrid). The study is expected to provide enriching information regarding recognizable clinical signs in the field that can lead to the diagnosis of streptococcosis caused by , especially in the Indonesian aquaculture environment.

METHODS

The method used in this artificial infection study using red tilapia, which were divided into two types of route groups infection, namely intraperitoneal (IP) and peroral (PO) with bacterial concentrations given for each route of infection to be 2.1 × 10 CFU ml; 2.1 × 10 CFU ml; and 2.1 × 10 CFU ml. One group was given brain heart infusion broth media sterile as a non-infectious control. Clinical symptoms, changes in swimming habits and consuming feed, external and internal organ lesion, and leukocytes profile changes were observed during the observation period along 14 days to evaluate the infectious effect of each treated fish group. The lethal dose 50 (LD) was estimated with the Spearman-Kärber method. The evaluation of the leukocyte profile was performed to find leukocytosis as the clinical sign of infection.

RESULTS

The results showed variations in clinical symptoms inflicted on fish through death or the moribund stage. The highest mortality occurred in the treatment group of 2.1 × 10 CFU ml with the PO route. The bacterial concentration of 2.1 × 10 CFU ml given either as PO or IP can cause mild infection symptoms but did not cause mortality. The LD of the PO and IP route was obtained at 1.99 × 10 CFU ml and 0.79 × 10 CFU ml, respectively. The total leukocytes in the infected fish group increased significantly ( < 0.05) by twofold when compared with the non-infectious group. The bacteria's discovery on the blood smear examination was taken from fresh dead fish or moribund fish in the treatment group of 2.1 × 10 CFU ml, for both PO and IP.

CONCLUSION

with low pathogenicity can lead to septicemia, characterized by a total increase in leukocytes, bacteria's discovery on the blood smear examination, and various clinical symptoms systemically found in the treated fish.