White fish are also called demersal fish. They live on, or near the sea-bed and may be round or flat. Round fish live near the sea- bed, e.g. cod, coley. Flat fish live on the sea bed, e.g. plaice.
Oil-rich fish are also called pelagic fish. They swim near the surface of the sea and are found in shoals, e.g. herring, mackerel.
Shellfish such as Lobster and Crabs, are all invertebrates (i.e. do not possess an internal skeleton) and are split into two main groups: molluscs have either an external hinged double shell (e.g. scallops, mussels) or a single spiral shell (e.g. winkles, whelks), or have soft bodies with an internal shell (e.g. squid, octopus); crustaceans have tough outer shells which act like armour, and also have flexible joints which allow quick movement (e.g. crab, lobster).
This checklist summarises the main points to look for when choosing fish.
- Clear, bright eyes, not sunken
- Bright red gills
- Scales should not be missing and they should be firmly attached to the skin
- Moist skin. Really fresh fish feels slightly slippery
- Shiny skin with bright natural colouring
- Tail should be stiff and the flesh feel firm
- It should have a sea-fresh smell
- Neat, trim fillets with firm flesh
- Fillets should be firm and closely packed together, not ragged or gaping
- White fish should have a white translucent colour with no discolouration
- Glossy appearance
- Flesh should feel firm and not sticky
- Pleasant, smoky smell
- Frozen hard with no signs of thawing
- The packaging should not be damaged
- No evidence of freezer burn (i.e. dull, white, dry patches)
- shells should not be cracked or broken
- Shells of mussels and oysters should be tightly shut. Open shells that do not close when tapped sharply should be discarded
- Lobsters, crabs and prawns should have a good colour and be heavy for their size
- Lobsters and crabs should have all their limbs
Once fish has been selected, it has to be handled and stored carefully. Spoilage is mainly caused by the actions of enzymes and bacteria.
Enzymes are present in the gut of the living fish and help convert its food to tissue and energy. When the fish dies, these enzymes carry on working and help the bacteria in the digestive system to penetrate the belly wall and start breaking down the flesh itself.
Bacteria exist on the skin and in the fish intestine. While the fish is alive, the normal defence mechanisms of the body prevent the bacteria from invading the flesh. Once the fish dies, the bacteria invade the flesh and start to break it down, the higher the temperature the faster the deterioration. (Note these bacteria are harmless to humans)
Fish, once caught, has a shelf life of I0 to 12 days if kept properly on ice. (Comment:- but at their best in the first 5 days. Jeff)
In a refrigerator the storage temperature should be between 0°C and 5°C.
Fresh fish: Fresh fish should be used as soon as possible, but it can be stored overnight. Rinse, pat dry, cover with cling film and store towards the bottom of the refrigerator.
Ready-to-eat cooked fish such as "hot" smoked mackerel, prawns and crab should be stored on shelves above other raw foodstuffs to avoid cross-contamination.
Smoked fish: Smoked fish should be well wrapped up and kept separate from other fish to prevent the smell and dye penetrating other foods.
Frozen fish: In the home, frozen fish should be stored at -18°C or less. It should be thawed out overnight in a refrigerator. It should NOT be thawed out in water as this spoils the taste and texture of the fish and valuable water-soluble nutrients are lost. Fish should not be re-frozen as this will impair its taste and texture.