ARS | Publication request: HEMATOLOGICAL CHANGES IN NILE TILAPIA (OREOCHROMIS NILOTICUS) INFECTED WITH STREPTOCOCCUS INIAE BY NARE INOCULATION

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2003
Publication Date: September 1, 2003
Citation: MCNULTY, S.T., KLESIUS, P.H., SHOEMAKER, C.A., EVANS, J.J. HEMATOLOGICAL CHANGES IN NILE TILAPIA (OREOCHROMIS NILOTICUS) INFECTED WITH STREPTOCOCCUS INIAE BY NARE INOCULATION. JOURNAL OF THE WORLD AQUACULTURE SOCIETY. 2003. vol 34 (3):418-422.

Interpretive Summary: Streptococcus iniae causes over $150 million in economic losses to fish farms, worldwide. This bacterium infects over 22 species of fish, cultured and wild fish in fresh and marine water. Early detection of the disease could dramatically reduce the losses and allow early detection of disease outbreaks. We found that changes in hematological values were an early indication of disease in Nile tilapia. A sudden and dramatic decline in red blood cell counts accompanied by an increase in mean corpuscular volume were the most common indictors of S. iniae infections. We conclude that changes in blood parameters of infected fish are early indicators of infection and disease.

Technical Abstract: There is little or no information on the effects of Streptococcus iniae infection on the hematology in Nile tilapia(Oreochromis niloticus). This study characterized the hematological changes in juvenile and adult tilapia infected with S. iniae by nare inoculation. The hematological values measured included mean hematocrit (%), mean red blood cell count RBC (10**6/uL), mean total hemoglobin (g/dL), mean corpuscular volume MCV(fL), mean corpuscular hemoglobin MCH(pg), and mean corpuscular hemoglobin concentration MCHC(g/dL). Blood samples were collected for the control fish, 2 days post inoculation(DPI), 5 DPI, and 7 DPI. We observed that S. iniae infection caused a significant change in hematological values. The most dramatic change was the reduction in red blood cell counts. In the juvenile tilapia, the RBC count was significantly (p</- 0.05) different from the controls and had a range of 3.9 +/- 1.6 to 1.4 +/- 0.6 x 10**6uL. The RBC counts in the adult tilapia were significantly (p</- 0.05) different from the controls to 7 day post inoculation (DPI) and had a range of 4.64 +/- 2.7 to 1.19 +/- 0.3 x 10**6/uL. The decrease in mean RBC counts may be due to the hemolytic nature of S. iniae. The study indicated that S. iniae infection alters the hematology of both juvenile and adult Nile tilapia.