Abstract

Microcystin-LR (MC-LR) and nodularin are cyanobacterial metabolites found worldwide in freshwater and brackish environments. Exposure to algae-contaminated water has caused acute toxicosis in both animals and humans. These compounds accumulate, probably as a result of irreversible binding to liver protein phosphatase. In a previous study utilizing channel catfish (Ictalurus punctatus), we developed methods for the analysis of MC-LR and nodularin in both orally and intraperitoneally (IP) treated fish. However, the chemical analysis of both the nodularin-treated fish and their controls exhibited the presence of a compound chemically similar to microcystin-LR.

Since positive findings were observed only in IP-treated fish, we repeated this portion of the original study. Seven channel catfish were treated IP with 250 micrograms/kilogram (µg/kg) of MC-LR, and seven fish were treated with 250 µg/kg of nodularin. Seven control fish were treated with the vehicle used for preparing the treatment solutions (2:8 ethanol:PBS). Blood and liver samples were collected from the fish 24 hours after dosing for histopathological examination and chemical analysis. The analysis of both liver and blood samples from the MC-LR and nodularin treatment groups as well as the control groups was performed using pre-established methods with a triple quad LC/MS/MS.

The fish treated with MC-LR had detectable residues in both liver (range 566–1030 ppb) and serum (range 370–670 ppb). The nodularin-treated fish also had positive liver (range 859–1140 ppb) and serum (range 853–1520 ppb) results. No peaks for MC-LR or nodularin were detected in any of the control fish. Similar to the previous study, livers from the MC-LR and nodularin-treated fish showed hepatocellular individualization and necrosis, with the MC-LR lesions appearing somewhat more severe than those associated with the nodularin.

Acknowledgements

The authors wish to thank Ms. Nina Richey for her help with sample preparation for this study.

* Presenting author