Aquaculture expansion in the United States has brought novel challenges as producers look to magnify and diversify their operations. Recent data has indicated increased largemouth bass (LMB; Micropterus salmoides) production as culturists aim to capitalize on the high market value. While this lucrative opportunity has provoked much interest, production facilities must navigate LMB through their critical early-life stages. As one of the leading causes of mortality in warmwater culture, motile Aeromonas septicemia (MAS; including Aeromonas hydrophila and Aeromonas veronii) poses a significant threat to production facilities. Providing culturists with practical alternative tools to combat disease, such as autogenous vaccines, can be valuable for reducing mortality.
To determine the optimal timeframe for vaccinating LMB fingerlings, three experimental vaccination periods of 0-, 2-, and 4-months will be studied. At time 0 the fish will be ~5 g. For each experimental timepoint, formalin-killed cultures of A. veronii (ARS-LMB-32-2018) and A. hydrophila (ARS-LMB-2022-09) will be administered via a 30 min static immersion bath. The LMB will be monitored for 30 days post-vaccination (dpv) to allow the specific immune response to be generated. Thereafter, spleen, kidney, and distal intestines will be sampled at 0-, 15-, and 30 dpv for targeted gene expression to assess vaccine-induced immune responses. Microbial gut communities will also be characterized. At these times, sera will also be collected to evaluate Aeromonas spp.-specific antibody titers via ELISA. Additionally, morphometric analyses will be conducted to observe notable changes in response to vaccination. At 30 dpv, LMB will be challenged using a standardized fin-clip methodology and subjected to a 1 h static bath at ~2×107 CFU mL-1. Cumulative percent mortality will be monitored incrementally through the 7-day challenge duration.
With this long-term study, we aim to improve the understanding of LMB fingerling response to formalin-killed immersion bath vaccinations of A. veronii & A. hydrophila and the potential for mortality reduction. Data collection of 2- and 4-month timepoints is underway and future results will be discussed upon completion. Studies such as these will provide vital information to producers to reduce mortality, avoid antibiotic usage, and increase product security as the culture of the species expands for food-fish production.