Flesh and viscera/gill tissues of six amberjacks (Seriola dumerilii), suspected positive for ciguatoxins, were each extracted and the toxins partially purified. Both flesh and viscera/gill of only five fish were toxic to mice exhibiting ciguatoxins (CTX) symptoms. The methanol extracts of the five fish were pooled and concentrated, the volume of flesh extract was 50.0 mL (129.4 mg toxins/mL) and viscera/gill had 25.0 mL (25.5 mg toxins/mL). Pooled extracts exhibited CTX symptoms in mice but only flesh killed mice in 6 h and the LD50was 1.72 mg toxins. The lethal potencies of the pooled flesh killed mice in 6 h and the LD50was 1.72 mg toxins. The lethal potencies of the pooled flesh was 198.17 g fish, equivalent to 58.3 mouse unit. An efficient fractionation and purification procedure was developed for the extracts using an HPTLC and silica gel 60 plate with a chromatographic solvent mixture of chloroform:methanol:water (60:35:8, v/v). The system yielded 10 fractions for flesh and 9 for viscera/gill. Scanned plates were subdivided into three equal zones, each scraped, methanol extracted and tested in mice. The 2nd zone (Rffractions between 0.40 and 0.66) was very toxic to mice compared to 1st or 3rd zones and the mice had CTX symptoms. The scanner for this 2nd zone had a cluster of minor peaks on both sides of the major one with a sum total area of 62.47% indicating multiplicity of CTX in amber‐jack fish. The major peak, at retention time of 1.48 s and a single area of 43.28%, is believed to be the main ciguatoxins present. The HPTLC is a rapid and sensitive procedure for ciguatoxins in fish flesh extracts with a detection limit of 40.0 ± 1.9 picogram toxi
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