classifications of fish


There are 3 main classifications of fish:

  • White fish has flesh that is white in colour and contains less fat. White fish can be round or flat, e.g. cod, haddock.
  • Flat fish - examples include plaice, sole and halibut.
  • Oily fish has flesh that is coloured and contains more fat than white fish but this is healthy fat with fish oils. Examples include salmon, sardines, mackerel and tuna.

There are 2 main classificatios of shellfish:

  • Crustaceans - crabs, lobsters, prawns, crayfish, shrimp and squid (which has a hard backbone that must be removed during preparation).
  • Molluscs - oysters, mussels, scallops, winkles and cockles.
1 of 5

Buying quality fish and preserving fish


To ensure you are buying quality fish, you need to make sure that; eyes are bright, not dull; scales are in place; gills are bright red; it has a slightly salty, fresh smell of the sea (fish smells bad as it deteriorates); it has a thin layer of slime; the flesh is firm.


There are a number of ways to preserve fish:

  • Canning - cans are heated to 121*C to kill bacteria; this heating creates a vacuum inside the can. Any blown or dented cans can cause food poisoning as the vacuum is broken and clostridium botulinum food poisoning can occur.
  • Freezing - sea fish are frozen within 90 minutes of capture to a minimum temperature of -18*C. This stops food-poisoning bacteria from reproducing and forces the bacteria to become dormant - it doesn't kill the bacteria.
  • Smoking - to 76*C or above, removes moisture from the fish and gives a distinctive flavour, e.g. smoked salmon.
  • Salting - salt is added to fish to remove its moisture. Food-poisoning bacteria cannot survive without moisture.
2 of 5

Preparing raw fish


  • Use a blue chopping board (sanitized).


  • Use a filleting knife to descale and remove the fins. Cut off the head just behind the gills.
  • Cut from head to tail down the bone, to one side of the centre line.
  • Turn the knife almost parallel to the table. Cut horizontally against the backbon towards the outer edge. Separate the fillet from the bone and remove it.


  • Descale and remove the fins. Cut into the top of the fish on one side of the tail; detach the backbone from head to tail.
  • Cut under the fles towards the tail and detach the cut piece.
  • Cut along the curved rib bones and finish detaching the fillet at the head. Turn  over and repeat to remove the second fillet.
3 of 5

Cooking raw fish

Fish cooks quickly because the muscle is short and the connective tissue is thin. The connective tissue is made up of collagen and will change into gelatin and coagulate at 75*C. Fish can be grilled, baked or fried. Often fish is enrobed in breadcrumbs/batter to protect it when using high heat. Fish can also be cooked gently by steaming or poaching without coating the flesh.

4 of 5

Nutritional Content and Storage Information


Nutrients in fish include:

  • Protein - for growth and repair.
  • Minerals - iron, zinc and iodine - for red blood cells, metabolism and to regulate blood sugar.
  • Vitamins A and D - for vision, body linings, immune system, bone health, and to help with mineral absorption.

Oily fish contains omega 3 fatty acids for brain development, healthy bones and joints.


  • Most fresh fish is best eaten on the day it has been bought as it can spoil very quickly and be unsafe to eat.
  • Shellfish must be prepared and eaten within 2 days of purchase.
  • Fresh fish must be stored in the refrigerator. Ice is often used to store fish on boats and in supermarkets to keep it fresh.
  • Fresh fish can be frozen on the day it has been bought and stored for several months; it must be defrosted before use.
5 of 5


No comments have yet been made

Similar Design & Technology: Food Technology resources:

See all Design & Technology: Food Technology resources »See all Nutrition resources »