EXPERIMENTAL INDUCTION OF Aeromonas hydrophila IN TILAPIA FINGERLINGS ON A NOVEL ANTIBODY DIET

Aquaculture is the fastest growing animal-production sector for food in the world. Health and safety issues are prevalent among aquatic animals during massive growth and production. Disease outbreaks within aquaculture facilities can cause economic losses in the billions. Antibiotics are currently in use in aquaculture as a therapeutant for treating disease. However, over time the use of antibiotics has brought up a new set of issues; antibiotic resistant bacteria/genes and transfer of these to the environment and to humans via consumption. For this reason, efforts are underway to replace antibiotics, while maintaining a safe and high quality environment for the animals.

The up-regulation of interleukin-10 (IL-10), an anti-inflammatory cytokine, has been determined by recent studies as the reason for lack of immune detection by gastrointestinal pathogen invasion. This study focuses on the use of anti-IL-10 egg yolk antibody in tilapia fingerling diet as a neutralization of IL-10, when challenged with pathogen, Aeromonas hydrophila. To understand the effectiveness of the anti-IL-10 diet in tilapia fingerlings, the diet was administered for at least 3 days prior to an experimental induction of A. hydrophila by both immersion and oral gavage. Method development for experimental-induction is still underway. Survival rates for these preliminary studies were monitored for at least 24h post-induction.

Duplicate trials of immersion were completed using tilapia fingerlings exposed to 1-2 x 10⁶ CFU/ml of A. hydrophila in trial 1 and 7-9 x 10⁷ CFU/ml in trial 2. Results showed 100% survival throughout all treatments in trial 1. In trial 2, the control diet challenged with A. hydrophila treatment resulted in 73.34%  18.85 survival, while the treatment fed the anti-IL-10 diet and challenged with A. hydrophila resulted in 50%14.14 survival.

Duplicate trials of induction by oral gavage were also studied to compare the effects of different routes of exposure. The volume gavaged was dependent on fish weight; 0.02ml of A. hydrophila (grown in in Tryptic Soy Broth) per gram of fish. In the first oral gavage trial, fingerlings were dosed 1-2.5 x 10⁶ CFU/g fish of A. hydrophila. The survival rates were 96.65%4.74 and 86.65% 18.88 for control diet and anti-IL-10 diet, respectively. The second trial was done by gavaging A. hydrophila over various time points on the bacterial growth curve; 2, 4, and 5.5 hours of growth. Concentrations gavaged included 2.78 x 10⁶ CFU/g fish (2h growth), 1.68 x 10⁷ CFU/g fish (4h growth), and 3.72 x 10⁷ CFU/g fish (5.5h growth). The survivability of fish on the 2h culture was 87.5% (control diet) and 75% (Anti-IL-10 diet), on the 4h culture, 87.5% (control diet) and 75% (anti-IL-10 diet), and on the 5.5h culture, 75% (control diet) and 100% (anti-IL-10 diet). Results are preliminary, as method development of these studies are progressing.