Abstract

Probiotic applications in aquaculture are aimed at preventing infection and improving overall fish health.³ Implementing methods of disease prevention and treatments are essential for minimizing economic loss and production setbacks. A variant of Edwardsiella ictaluri, a known bacterial pathogen of channel catfish, has caused widespread mortality in the tropical fish industry over the past decade, primarily affecting zebrafish (Danio rerio), a species important to aquarium and laboratory trades.^1,2 The objective of this study is to characterize the effects of probiotic treatment on the prevalence of E. ictaluri and to ascertain the effect on the gastrointestinal microbiota of fish.

Here, we tested two commercial probiotics (A and B) at two different fish farms. At each farm, 3 ponds were dosed with probiotic A, 3 ponds with probiotic B, and 3 ponds acted as the control group (no probiotic). Probiotics were selected based on laboratory inhibition of E. ictaluri. Farm operations were not altered except for probiotic additions. At each farm, during initial stocking and at two subsequent time points, pond water and 3 male and 3 female zebrafish (larval, juvenile, and adult/harvest life stages) were collected, dissected, and preserved for processing. Length, girth, and weight measurements were recorded for juvenile and adult/harvest stages. Microbial DNA data was collected from larval fish prior to pond stocking. Feces was collected from the gastrointestinal tract and samples are currently being processed for sequencing.

Fish size was highly variable between ponds and no significant difference between treatments was detected. Our project was impacted by the COVID-19 lockdown orders, so our sample collection schedule and processing procedures were delayed. We plan to compare larval and adult microbiomes to determine if the probiotics alter microbial composition of the gastrointestinal tract. We will also compare the presence and abundance of E. ictaluri in Probiotic A, Probiotic B, and control fish and pond water to address effects on the presence and abundance of E. ictaluri. We hypothesize that the abundance of E. ictaluri will be reduced in the ponds treated with probiotics compared to control ponds. These data will be presented and discussed.

Acknowledgements

We thank the USDA NIFA Southern Regional Aquaculture Center for funding. EBR is supported by the National Science Foundation Graduate Research Fellowship (Program Grant No. 2019285699). Any opinions, conclusions or recommendations expressed in this work are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

*Presenting author
+Student presenter

Literature Cited

1.  Aristizabal-Henao JJ, Ahmadireskety A, Griffin EK, Da Silva BF, & Bowden JA. 2020. Lipidomics and Environmental Toxicology: Recent Trends. Curr Opin Environ Sci Health.

2.  Hawke JP, Kent M, Rogge M, Baumgartner W, Wiles J, Shelley J, Savolainen LC, Wagner R, Murray K, Peterson TS. 2013. Edwardsiellosis Caused by Edwardsiella ictaluri in Laboratory Populations of Zebrafish Danio rerio. J. Aquat. Anim. Health 25:171–183.

3.  Van Doan H, Hoseinifar SH, Ringø E, Ángeles Esteban M, Dadar M, Dawood MA, Faggio C, 2020. Host-associated probiotics: a key factor in sustainable aquaculture. Rev. Fish. Sci. Aquac. 28:16–42.