What to do right after the catch, keeping fish cold on the way home, gutting and cleaning, and avoiding parasites and food poisoning.
A fish starts to spoil the moment it is caught. Left somewhere warm, bacteria multiply fast, the flesh softens, and parasites in the gut can move into the flesh. So if you plan to eat your catch, think of cleaning as starting right after the catch, not when you get home. There are three rules: handle it quickly, keep it cold, and use clean hands and tools. Release fish you will not eat before any of this starts.
Letting a fish thrash for a long time pushes blood into the flesh and spoils the taste. A widely used method is to stun fish you keep quickly with a blow to the head or a cut at the right spot, then sever the blood vessels by the gills and hold the fish in water briefly to bleed it. Bleeding reduces the fishy smell and helps it keep. Sharp gill covers and fin spines cut hands easily during this, so wear gloves and hold the fish with pliers. Some fish carry venom in their spines, so do not grab unfamiliar fish bare-handed.
Put bled fish straight into a cooler packed with ice. At sea, many people mix a little seawater into the ice so the fish cool evenly. Freshwater ice in direct contact with the flesh for a long time can damage or soften the surface, so placing fish in a plastic bag on the ice is another option. Keep the cooler in the shade and do not open the lid often. Keeping fish alive in a bucket for hours actually makes things worse as the water warms.
Clean the fish as soon as you can once home. Scrape the scales from tail to head, open the belly and remove the guts, then scrape out the blood line along the spine with a brush or knife tip and rinse in clean water. Burst guts or gallbladder leave a bitter taste and smell in the flesh, so cut shallowly. Use a separate board and knife for fish, or wash them right after use, to prevent cross-contamination. Pat the fish dry when done; it cuts down on smell and bacterial growth in storage.
The guts of sea fish can contain anisakis larvae, which can move into the flesh as time passes after death. Gutting quickly is the first line of prevention, and when eating raw, check visually as you slice the flesh thin. Cooking thoroughly or freezing thoroughly kills the larvae. The U.S. Food and Drug Administration gives a standard of freezing at minus 20 degrees Celsius or below for 7 days, but home freezers may run warmer than that. Freshwater fish carry parasites such as liver flukes, so as a rule do not eat them raw. If you get severe stomach pain after eating raw fish, see a doctor.
In summer, Vibrio bacteria multiply easily in seawater. They thrive in salty conditions and are weak in fresh water, so rinse cleaned fish and boards thoroughly under clean tap water. Be especially careful with hygiene for fish you will eat raw, and do not eat anything left at room temperature for long. Poisonous fish such as pufferfish should never be cleaned by anyone but a qualified professional, whatever their taste or size, and it is safest not to eat any fish you cannot identify with certainty. People with liver or kidney conditions are advised to avoid raw seafood; if that applies to you, eat it cooked.
Pat cleaned fish dry, divide it into single-meal portions, seal it and keep it in the coldest part of the fridge. Refrigeration assumes you will eat it soon; freeze anything you will not eat right away from the start. Wrapping tightly in film or vacuum-sealing to keep out air reduces freezer burn. Thaw slowly in the fridge, and never refreeze fish once it has thawed.
Common mistakes are leaving fish in a bucket in the sun without a cooler, spending the day with the guts still in, cutting vegetables with the same knife and board straight after, and eating freshwater fish raw. When you give fish to others, tell them when it was caught and how it was stored. This guide is general hygiene advice; if symptoms of food poisoning persist, see a doctor.
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