Susceptibility of red tilapia (Oreochromis spp.) in normal and high water temperature: Streptococcosis play a role?

Objective: To determine the role of water temperature in disease development by Streptococcus agalactiae infection in red tilapia Method & Materials: There were four bacterial concentrations used; 6.3 x 106, 6.3 x 107, 6.3 x 108 and 6.3 x 109. The experimental trial was divided in three groups based on the stages of tilapia, including group 1 (fingerlings: mean weight 17g), group 2 (adults: mean weight 98g), group 3 and group 4, which comprised of fingerlings and adults, served as control groups. The bath immersion technique was used for group 1, while group 2 was injected intraperitoneally. Twenty fingerlings were immersed into 2L of bacterial broth and 15 adults were subjected to injection. Results & Conclusion: Lethal dose 50 (LD50) for fingerlings with S. agalactiae was 2.9242 x 1020 in normal water temperature, while 1.49 x 1010 in high water temperature. However, in adults, LD50 was 2.3884 x 107 in normal water temperature and 1.31 x 105 in high water temperature. No mortality was observed in group 3 and 4. The results indicated that high water temperature plays a significant role in stressing out the fish and eventually leads to poor immunity response against infections.

کلیدواژه ها:

Streptococcus agalactiae ، disease development ، LD50 ، temperature ، red tilapia