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Title: Growth Response and Acquired Resistance of Nile Tilapia Oreochromis niloticus Following Infection or Vaccination with Streptococcus iniae

item Shoemaker, Craig
item Lim, Chhorn
item Aksoy, Mediha
item Welker, Thomas
item Klesius, Phillip
item Evans, Joyce

Submitted to: International Symposium on Talipia in Aquaculture
Publication Type: Proceedings
Publication Acceptance Date: 8/4/2006
Publication Date: 9/1/2006
Citation: Shoemaker, C.A., Lim, C.E., Aksoy, M., Welker, T.L., Klesius, P.H., Evans, J.J. 2006. Growth Response and Acquired Resistance of Nile tilapia Oreochromis niloticus Following Infection or Vaccination with Streptococcus iniae. Proceedings 7th International Symposium on Tilapia in Aquaculture (ISTA7). September 6-8, 2006. Veracruz, Mexico. p. 43-48.

Interpretive Summary: Streptococcus iniae is a Gram-positve bacterium responsible for tens of millions of dollars in annual losses to the tilapia and hybrid striped bass aquaculture industry in the US. Little information is available on the growth of fish following infection or vaccination with Streptococcus iniae. Literature from other animal species suggests that growth is decreased following infection and/or vaccination. The results of the current studies suggest that vaccinated tilapia or tilapia that survived S. iniae infection produced a protective immune response and gained acquired resistance to S. iniae. We further showed that growth and feeding response of infected or vaccinated tilapia did not differ from uninfected (i.e. control) tilapia. Vaccination of aquatic animals will provide for protection from aquatic pathogens and will have an overall beneficial effect on growth and performance

Technical Abstract: Growth performance and acquired resistance of Nile tilapia, Oreochromis niloticus (L.) that survived Streptococcus iniae infection was determined. Tilapia were challenged with three doses of S. iniae (8.8 x 10 to the 3rd power, 8.8 x 10 to the 4th power and 8.8 x 10 to the 5th power CFU fish-1 for low, medium and high challenges, respectively). Groups of non-injected and tryptic soy broth-injected fish were maintained as controls. Significantly (P < 0.05) higher mortality (45.0 %) occurred in the high challenge treatment than in the low challenge treatment group (29.6 %). The medium challenge group had mortality (36.3 %) that did not differ significantly from the high or low treatment. Few fish died in the non-injected and broth-injected treatments (3.4 and 0.8 %, respectively). The tilapia that survived S. iniae infection and used to assess growth performance were selected from survivors without gross clinical signs of disease. These fish were randomly stocked at a rate of 30 fish into each 57-L aquarium in triplicate and fed to apparent satiation twice daily for 8 weeks. No significant differences were detected in weight gain, feed intake, feed efficiency ratio or survival between S. iniae-survived tilapia and the control treatments following the 8-week growth performance trial. After the 8-week feeding study, tilapia were challenged with 1 x 10 to the 6th power CFU fish-1 of S. iniae to assess acquired immunity. Mean cumulative mortality was significantly higher (P < 0.05) in the control treatments (41.7 % for the non-injected and 43.3 % for the broth-injected fish) than in the low, medium and high challenge treatments (7.4, 3.3 and 8.3 %, respectively). Serum protein was significantly (P < 0.05) elevated in S. iniae-survived tilapia that were subsequently challenged when compared to controls challenged for the first time. Agglutinating antibody titer was significantly higher in the fish in the medium and high challenge treatments, compared to the control fish challenged for the first time. Tilapia surviving S. iniae challenge without showing overt disease signs performed as well as non-infected tilapia and gained acquired resistance to homologous S. iniae challenge.