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Effects of Microcystin-LR on channel catfish susceptibility to microbial pathogens
Proceedings of the 2022 Mississippi Water Resources Conference

Year: 2022 Authors: Marchant A., Ford L., Petrie-Hanson L., Peterman B., Hanson L.

Cyanobacterial blooms have become increasingly common in natural water bodies and aquaculture systems. These blooms can release several toxins that are health risks for many species including humans, domesticated animals, wildlife, and fish. The most studied environmentally stable toxin produced by cyanobacteria is the hepatotoxin, Microcystin (MC-LR). Channel catfish (Ictalurus punctatus) ponds often have blooms that express MC-LR, but losses due to the toxin are rare. However, we believe that the toxin may be a predisposing factor of losses in catfish to summer pathogens due to the effects that MC-LR has on the liver. In our studies, we investigated the effects of a known dosage of MC-LR on the channel catfish liver, and its effects on channel catfish susceptibility to the summer bacterial pathogens Edwardsiella piscicida and Aeromonas hydrophila. In the first trial, treatment fish were intracoelomically injected with a 500 ng/g bw dose and were sampled along with control fish over a 6-day period. The MC-LR treated fish were not visibly affected but completely stopped eating, when sampled all treated fish through day 4 had no ingesta and had full gall bladders, most control fish demonstrated ingest a in the gut and lighter colored typical gall bladders. Serum aspartate aminotransferase and alanine aminotransferase levels were significantly elevated from 6 hours through 96 hours post-exposure indicating hepatotoxicity. Alkaline phosphatase and bilirubin levels were not substantially affected. Histology confirmed substantial hepatic injury among the treated fish. Later trials that contained both MC-LR and the bacterial pathogens resulted in significantly greater mortality in the treatment group containing both MC-LR and the bacteria in comparison to bacteria only treatments, and no losses within only MC-LR. Our study demonstrated exposure to subclinical doses of MC-LR, can compromise the function of the liver and digestive system and these are critical organs of the innate immune defenses which may have resulted in the increased mortality when encountering bacterial pathogens.

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