Keeping a catch safe to eat

If there is one transferable idea in this subject it is that the quality and safety of a caught fish are determined in the first hour, and that nothing done later recovers what is lost in it.

DISPATCH, BLEED, CHILL — IN THAT ORDER AND WITHOUT DELAY. Each step matters and the order is not arbitrary. A fish dispatched promptly stops struggling, which stops the muscle chemistry that degrades texture. Bleeding while the heart is still working removes far more blood than bleeding a dead fish. Chilling immediately slows bacterial growth, enzyme activity and every other spoilage process.

ICE SLURRY BEATS ICE, AND ICE BEATS A COOL BOX. A mixture of ice and water surrounds the fish and conducts heat away far faster than ice sitting beside it, and both are enormously better than a closed box that is merely shaded. On a hot beach or boat, an ungutted fish in a dry box is warm within minutes.

GUTTING EARLY HELPS MOST FISH, because the gut contains the enzymes and bacteria that cause the fastest deterioration, and removing them removes the problem. The exception is where the fish will be kept whole for a short period on very good ice.

SCOMBRID FISH ARE THE SPECIAL CASE AND THE MOST DANGEROUS ONE. Mackerel, tuna, bonito and their relatives accumulate histamine when held warm after death, through bacterial conversion of free histidine in the flesh. The resulting scombrotoxin poisoning is not destroyed by cooking, freezing or any later treatment, and it is caused entirely by inadequate chilling in the hours after capture. The record for albacore sets this out and it applies across the whole family.

FREEZING CONTROLS PARASITES AND DOES NOT CONTROL BACTERIA. Freezing at sufficiently low temperature for sufficient time kills the parasites of concern in fish intended to be eaten raw or lightly cured, and it is the recognised control for that specific hazard. It does nothing about histamine already formed or about spoilage that has already occurred.

AND REFREEZING RUINS TEXTURE, which is why portioning before freezing matters — the same principle the bait records describe for cut bait, applied to food.

Some risks in eating a catch have nothing to do with how it was looked after, and they matter because no amount of good practice addresses them.

SHELLFISH BIOTOXINS ARE THE CLEAREST CASE. Filter-feeding bivalves concentrate toxins produced by certain algae, and those toxins are not destroyed by cooking, cannot be detected by smell, taste or appearance, and can be present in animals that look perfect. This is why gathering grounds are classified and monitored and why closures exist. The catalogue's shellfish material and the records for mussel, cockle and razor clam all make the same point: whether a bed may be gathered from is a question for the local competent authority and is not answerable by inspecting the animal.

CIGUATERA IS A TROPICAL REEF HAZARD AND IT IS SPECIES- AND PLACE-SPECIFIC. Toxins accumulate up the reef food chain and concentrate in large predatory reef fish in particular areas. It is not destroyed by cooking and cannot be detected by inspection. Local advice on which species and sizes are safe in which locality is precise, authoritative and worth following exactly; advice learned in one ocean does not transfer to another, as the record comparing king and Spanish mackerel sets out.

PARASITES ARE COMMON, MOSTLY HARMLESS COOKED, AND CONTROLLED BY FREEZING. Nematodes in the flesh of many marine fish are ordinary rather than a sign of a bad fish. Thorough cooking deals with them; for fish to be eaten raw, cured or lightly smoked, freezing to the recognised time and temperature is the control.

CONTAMINANT ADVISORIES APPLY TO PARTICULAR WATERS AND PARTICULAR SPECIES. Mercury in large long-lived predators, and industrial contaminants in some rivers, estuaries and harbours, are the subject of published consumption advice — frequently with specific guidance for children and for people who are pregnant. Those advisories are issued by health authorities, they differ by water, and they change.

AND VIBRIO AND WOUND INFECTIONS ARE A HANDLING HAZARD RATHER THAN A FOOD ONE. Puncture wounds in warm brackish or coastal water can become seriously infected, which the records for catfish and for the Gulf of Mexico both note.

FISHINGHQ DOES NOT STATE WHETHER ANY WATER, SPECIES OR GROUND IS SAFE. The relevant food safety, health and fisheries authorities do, their advice is current where this page is not, and checking it is the whole of the answer.