C-CTX1 and 17-OH-C-CTX1 Accumulation in Muscle and Liver of Dusky Grouper (Epinephelus marginatus, Lowe 1834): A Unique Experimental Study Under Low-Level Exposure

This study investigated the bioaccumulation of ciguatoxins (CTXs) in dusky grouper (<i>Epinephelus marginatus</i>) following dietary exposure to toxic fish flesh. Two feeding groups were established: group A (amberjack (<i>Seriola</i> spp.) and dusky grouper flesh) and group B (moray eel (<i>Muraena</i> spp. and <i>Gymnothorax</i> spp.) flesh). CTX-like toxicity was detected in muscle and liver of group A. Flesh toxicity progressively increased from the first sampling. In contrast, CTX activity was only detected in livers in group B. Liquid chromatography-mass spectrometry analysis revealed the presence of C-CTX1 in both groups, and the 17-OH-C-CTX1 analogue was exclusively observed in group A. Toxicity in the liver peaked at 10 weeks in experimental group A, but it showed a decline by the end of the experiment while increasing the storage of the toxin in muscle tissue. These findings demonstrate the differential bioaccumulation of CTXs in grouper flesh and liver, highlighting the potential role of the liver in metabolizing and/or detoxifying ciguatoxins. The efficacy of a combination of different techniques, including the cell-based assay (CBA) and liquid chromatography-low- and high-resolution mass spectrometry (LC-MS/MS and LC-HRMS), was demonstrated to confirm the presence of CTX analogues at very low levels. The results provide insights into CTX transfer and accumulation in marine food webs, underlining the need for further studies on toxin metabolism in predatory fish species.