Giant Moray Eel (Gymnothorax javanicus), a Long-Living Apex Predator That Poses a Food Safety Risk in the Pacific

Abstract

The giant moray eel (GME; Gymnothorax javanicus) is an important marine species that plays a key ecological role in reef systems and is a valued food source for indigenous communities. However, it is well-known that GMEs pose a food safety risk due to their ability to accumulate high levels of ciguatoxins (CTXs), the toxins known to cause ciguatera poisoning. This study assessed the age, CTX levels, elemental composition, and nutritional profile of seven GME specimens collected from Muri Lagoon, Rarotonga (Cook Islands), representing the most detailed compositional investigation on this species. Age was determined for the three largest specimens, with the oldest being 39 years old. All specimens contained ciguatoxins, with Type I (CTX4A derivatives), Type II (CTX3C derivatives), algal-ciguatoxins, and biotransformed metabolites being detected. There was a higher CTX content in the liver samples compared to flesh samples, with the longest-heaviest specimen containing the highest levels. The CTX1B level observed in flesh samples of all seven eel specimens exceeded the recommended safe guidance level proposed by the USFDA. A similar ciguatoxin profile was observed across flesh sections, with the belly flap or top loin containing the highest levels of CTXs in most specimens. No bioactive metabolites produced by co-occurring harmful microalgae, including regulated shellfish toxins, were detected. Elemental analysis determined the presence of 21 elements, including arsenic, low levels of mercury, and the volcanic elements rubidium and strontium. Nutritionally, the GMEs were shown to be a lean protein source; however, due to the ubiquitous bioaccumulation of CTXs, they pose a food safety risk to consumers.

Keywords: aging; bioaccumulation; bioactive; ciguatera poisoning; ciguatoxin; elements; heavy metals; mass spectrometry; nutrition; toxicity.

Figure 1

Example structures of CTX Type I (CTX4A), showing the aliphatic hydrocarbon chain on ring A, and Type II (CTX3C) with the eight-membered ring E.

Figure 2

Phylogenetic analysis of mitochondrial cytochrome oxidase I (COI) gene sequences of the seven giant moray eels (Gymnothorax javanicus) specimens (in bold), collected from Muri Lagoon (Rarotonga, Cook Islands), analyzed with other Gymnothorax spp. sequences from GenBank using Bayesian analyses. Values at nodes represent Bayesian posterior probability support. Scale bar represents substitutions per site.

Figure 3

Images from the skull of the giant moray eel (Gymnothorax javanicus), specimen 2 (approximately 120 mm in length), collected from Muri Lagoon (Rarotonga, Cook Islands). (A) X-rays showing the left and right lateral views with the jaw closed and fully extended. (B) Photo of the neurocranium showing the location of the two sagitta otoliths (green arrows). (C) The left and right sagitta otoliths showing the concave dorsal depression and sulcal groove (convex side). (D) Cross-sectional view of the left-hand sagitta otolith used for aging.

Figure 4

Stacked total ion chromatogram of ciguatoxins observed in the liver from the giant moray eel (Gymnothorax javanicus) specimen 2, collected from Muri Lagoon (Rarotonga, Cook Islands).

Figure 5

Flesh sections were analyzed to determine if there was localized ciguatoxin bioaccumulation in giant moray eel (Gymnothorax javanicus) specimens, collected from Muri Lagoon (Rarotonga, Cook Islands). (A) top loin, (B) belly flap, (C) center loin, (D) tail section, and (H) head flap for GME specimens 2, 3, and 7 only.

Figure 6

Total ciguatoxin content for the flesh sections in the seven giant moray eel (Gymnothorax javanicus) specimens, collected from Muri Lagoon (Rarotonga, Cook Islands). A = top loin, B = belly flap, C = center loin, D = tail section, and H = head flap.

Figure 7

Comparison of ciguatoxin (CTX)1B levels observed in the flesh from the seven giant moray eel (Gymnothorax javanicus) specimens collected from Muri Lagoon (Rarotonga, Cook Islands). A = top loin, B = belly flap, C = center loin, D = tail section, and H = head flap. The green line represents the limit of quantitation, with values below this line reported as detected but not accurately quantified. The red line indicates the United States Food and Drug Administration-recommended guidance limit of 0.01 µg/kg CTX1B [22].