Abstract
Fish collected after a mass mortality at an artificial lake in south-east Queensland, Australia, were examined for the presence of nodularin as the lake had earlier been affected by a Nodularia bloom. Methanol extracts of muscle, liver, peritoneal and stomach contents were analysed by HPLC and tandem mass spectrometry; histological examination was conducted on livers from captured mullet. Livers of sea mullet (Mugil cephalus) involved in the fish kill contained high concentrations of nodularin (median 43.6 mg/kg, range 40.8–47.8 mg/kg dry weight; n = 3) and the toxin was also present in muscle tissue (median 44.0 μg/kg, range 32.3–56.8 μg/kg dry weight). Livers of fish occupying higher trophic levels accumulated much lower concentrations. Mullet captured from the lake 10 months later were also found to have high hepatic nodularin levels. DNA sequencing of mullet specimens revealed two species inhabiting the study lake: M. cephalus and an unidentified mugilid. The two mullet species appear to differ in their exposure and/or uptake of nodularin, with M. cephalus demonstrating higher tissue concentrations. The feeding ecology of mullet would appear to explain the unusual capacity of these fish to concentrate nodularin in their livers; these findings may have public health implications for mullet fisheries and aquaculture production where toxic cyanobacteria blooms affect source waters. This report incorporates a systematic review of the literature on nodularin measured in edible fish, shellfish and crustaceans.
Highlights
Cyanobacterial hepatotoxins and neurotoxins have long been known to cause death and acute illness in wild animals and livestock
Publications that used ELISA as the sole analytical method generally reported their results in terms such as “total cyanobacterial hepatotoxins” or “microcystin-LR equivalents”, as the ELISA kits used in most studies detect and quantify the ADDA moiety common to microcystins and nodularin
The studies in which ELISA alone was used are included in this table because reported exposures were to nodularin-producing cyanobacteria (Nodularia spumigena), i.e., exposure to microcystins or microcystin-producing cyanobacteria would appear to be unlikely or minimal
Summary
Cyanobacterial hepatotoxins and neurotoxins have long been known to cause death and acute illness in wild animals and livestock. Mass intoxications have been documented for over a century; such incidents led to the understanding that cyanobacterial waterblooms could be poisonous [1]. Nodularia spumigena and its associated toxin nodularin have a long history of poisoning stock animals and wildlife. The world’s first detailed scientific description of mass mortality attributed to toxic cyanobacteria concerned exposure to Nodularia-contaminated water in Australia. Horses, dogs and pigs were killed [2]. Cattle and dogs associated with exposure to Nodularia blooms in northern European waters has been reported [3,4]
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