Bowker An evaluation of the effectiveness of various florfenicol treatment regimens to control mortality caused by Streptococcus iniaei in cultured hybrid striped bass

This research endeavor is initiated with the purpose of examining alternate treatment regimens, specifically higher concentrations or extended treatment durations, beyond the standard protocol of 10 mg florfenicol per kg of fish body weight administered over 10 consecutive days. Our focus is on their potential for more effective control of mortality in hybrid striped bass (HSB), resulting from Streptococcus iniae infections.

Objectives

1. Using isolates of S. iniae, determine which route of infection (immersion or IP injection) of HSB that will consistently yield a mean cumulative mortality of 50% in the exposed group with the least statistical variation among replicates.  Also, identify important dose-dependent variables, such as: time to onset of first morbidity, time to first mortality, and total cumulative mortality.
2. Refine methodologies identified in #1 to consistently yield a mean cumulative mortality of 50% in HSB of a different age exposed to isolates of S. iniae.
3. Using the optimal dose and exposure route described in #2, determine the most effective treatment dose of florfenicol to control mortality in HSB experimentally infected with S. iniae fed a medicated feed top-coated with either 0, 10, 15, or 20 mg florfenicol/kg fish/d for 10 d. 
4. Using the lowest treatment dose that resulted in the highest survival (identified in #3), determine the most effective treatment duration of florfenicol to control mortality in HSB experimentally infected with S. iniae fed a medicated feed for either 0, 10, 15, or 20 days.  
5. Demonstrate and substantiate that the most efficacious treatment regimen identified in #4 is also effective when florfenicol is administered to HSB naturally infected with S. iniae (i.e. controlled field trial).