Haematological changes in Nile tilapia experimentally infected with Enterococcus sp.

Abstract

This study evaluated the haematological changes in Nile tilapia experimentally infected with 1 × 103 and 1 × 10 6 colony-forming units (CFU)/mL of Enterococcus sp. in the swim bladder. The experiment consisted of four treatments in triplicates: non-injected fish (NI); fish injected with 1 mL of sterile saline solution 0.65% (SAL); fish injected with 1 × 103 and 1 × 106 CFU/mL of Enterococcus diluted in 1 mL sterile saline. Twenty-four hours after injection, the fish were anesthetized and the blood collected. The haematological tests included red blood cell (RBC) and white blood cell (WBC) counts, hematocrit, number of total thrombocytes, and differential counting of WBC. Fish injected with 1 × 106 CFU/mL of Enterococcus showed a higher number of thrombocytes than the other treatments. White blood cell and lymphocyte numbers increased significantly in fish injected with 1 × 106 CFU/mL of Enterococcus when compared to non-injected control. There was significant increase in the number of neutrophils in saline injected fish and reduced number of monocytes after injections with 1 × 10 6 CFU/mL of Enterococcus. Hematocrit increased in fish injected with 1 × 103 and 1 × 106 CFU/mL of Enterococcus.