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Title: STREPTOCOCCUS INIAE INFECTION AND TISSUE DISTRIBUTION IN HYBRID STRIPED BASS (MORONE CHRYSOPS X MORONE SAXATILIS) FOLLOWING INOCULATION OF THE GILLS

Author
item McNulty, Shawn
item Klesius, Phillip
item Shoemaker, Craig
item Evans, Joyce

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2002
Publication Date: 4/4/2003
Citation: MCNULTY, S.T., KLESIUS, P.H., SHOEMAKER, C.A., EVANS, J.J. STREPTOCOCCUS INIAE INFECTION AND TISSUE DISTRIBUTION IN HYBRID STRIPED BASS (MORONE CHRYSOPS X MORONE SAXATILIS) FOLLOWING INOCULATION OF THE GILLS. AQUACULTURE 220(1-4) 2003 165-173

Interpretive Summary: Streptococcus iniae causes over $150 million in economic losses to fish farms, worldwide. This bacterium infects over 27 species of fish, cultured and wild fish in fresh and marine water. Several studies have been conducted to determine the route in which Streptococcus iniae enters the body of hybrid striped bass. This study was designed to test the possibility that S. iniae enters through the gills and causes infection in hybrid striped bass. We looked at the effect of dose on mortality and tissue dissemination. The results of this study indicate that S. iniae can enter hybrid striped bass through the gills. However, mortality at similar S. iniae doses was lower than we previously observed by inoculation of the nares.

Technical Abstract: Several studies have been conducted to determine the route in which Streptococcus iniae enters the body of hybrid striped bass. This study was designed to test the possibility that S. iniae enters through the gills and causes infection in hybrid striped bass. To determine the dose response, four groups of fish were inoculated with S. iniae via the gills with a dose of 5.0 x 105, 2.6 x 106, 5.0 x 106, or 1.0 x 108 CFU/ fish. One group of fish was inoculated with tryptic soy broth (TSB) via the gills to serve as controls. The cumulative percent mortality was 13.3%, 26.7%, 100%, and 100% for 5.0 x 105, 2.6 x 106, 5.0 x 106 and 1.0 x 108 CFU/ fish, respectively. We also examined the tissue dissemination of S. iniae at 0.5, 4, 8, 12, 24, 48, and 72 hours after experimental gill inoculation. Fish were inoculated with 2.6 x 106or 5.0 x 106 CFU/ fish, which caused low and high mortality, respectively. Within 48 h, fish inoculated with the 2.6 x 106 dose were culture positive on the gill surface, blood of the 1st and 2nd gill arches, blood of the 3rd and 4th gill arches, and the nares. However, for the dose of 5.0 x 106 CFU/fish, S. iniae was also isolated from the olfactory, optic, and cerebellum regions of the brain, eye, head kidney, trunk kidney, spleen, and liver at 48 h. For the 2.6 x 106 dose, S. iniae was not isolated until 48 h post inoculation, but was isolated at 12 h for the 5.0 x 106 dose. The results of this study indicate that S. iniae can enter hybrid striped bass through the gills. However, mortality at similar S. iniae doses was lower than we previously observed by inoculation of the nares.