Ciguatera fish-size risk

Ciguatera fish poisoning comes from ciguatoxin, a heat-stable compound produced by the dinoflagellate Gambierdiscus toxicus that grows on dead reef coral and macroalgae. Herbivorous fish (parrotfish, surgeonfish, rabbitfish) eat the alga and pick up the toxin. Predators (snapper, grouper, barracuda, moray, amberjack, mackerel) eat the herbivores, and the toxin bioaccumulates up the food chain. A 50-kg barracuda from an outer reef can carry >100× the toxic load of a 1-kg parrotfish from a lagoon.

Weight bands follow Fiji Ministry of Health & WHO Pacific guidelines: 0–5 kg low accumulation, 5–20 kg moderate (most market fish sit here), 20–50 kg high (>80% of historical ciguatera hospitalisations in Fiji are from this band), >50 kg very high (the largest individual fish in the catch, often trophy specimens — most risky to eat). Region adds: outer-reef drop-offs have the highest Gambierdiscus substrate, lagoons the lowest.

Month matters because warm-water stratification (Oct – early Apr) concentrates the toxin in the lower water column and slows its clearance from fish tissue — but the published Fiji Bureau of Statistics case-load data shows a clear Apr–Sep peak in reported ciguatera, driven by cooler-water fishing season and increased line-caught predator landings. Bands: 0–25 Very Low · 25–50 Low · 50–70 Moderate · 70–85 High · 85+ Very High.

• Not a guarantee. Two fish of the same species, weight, region and month can carry different toxic loads — ciguatoxin is unevenly distributed within tissues. The liver, gonads, and head carry 5–10× more than the fillet.
• Not a diagnostic tool. If you have GI or neurological symptoms (cold-heat reversal, tingling, metallic taste) after eating reef fish, see a clinician — ciguatera is reportable in Fiji and treatment is supportive but real.
• Doesn't model cooking. Ciguatoxin is heat-stable — boiling, grilling, frying does not destroy it. Freezing doesn't either.
• Doesn't distinguish wild-caught from aquaculture. Farmed fish in Fiji are mostly milkfish (given) and prawns, both low-risk.
• Not medical advice. People with pre-existing neurological conditions, pregnant women, and children should treat any score above "Low" as "do not eat".