Abstract
Ciguatera fish poisoning (CFP) is a common syndrome affecting coastal communities in the Atlantic and Indo-Pacific regions, including the Greater Caribbean. This severe illness is caused by the ingestion of reef fish contaminated with ciguatoxins (CTXs). The source of CTXs has been associated with epiphytic dinoflagellates of the genus Gambierdiscus (among others) which reside on macroalgae that are grazed by herbivores. The entry of algal CTX precursors (often referred to as gambiertoxins) into the food web initiates a cascade of trophic transfer events and biotransformations that have not yet been fully elucidated in the Greater Caribbean region. A critical knowledge gap addressed in the present study was to gain better predictive capability of CTX presence in fishes across trophic levels in a sub-tropical hotspot for CFP (i.e. the Florida Keys). A variety of fish including herbivores (e.g., representatives of Acanthuridae and Pomacathidae) up to apex predators (e.g., Sphyrena barracuda and Mycteroperca bonaci) were collected from a long-term monitoring site in the Florida Keys. Extracts of fish were assessed for neurotoxicity and CTX activity using the sensitive in vitro neuroblastoma (N2a) assay. Twenty five of the 66 fish (38%) examined in this study expressed sodium channel-dependent toxicity in both sensitized and non-sensitized cell treatments, highlighting the likely presence of multiple toxin classes in these reef fish. Monospecific sodium channel activity was observed in 3% of fish represented by one species: S. barracuda. Stable isotope analysis was used to determine fish trophic level and in the calculation of a food web magnification factor (FWMF) of 1.114 for CTX and CTX-like compounds, indicative of the biomagnification of these toxins. The presence of toxic fish indicates a need for risk assessment and management consideration in the Florida Keys.