Fish are broadly classified as Finfish and Shellfish
Finfish are divided into white fish and oil-rich fish.
White fish are sometimes referred to as "lean fish" because all the oils are contained in the liver, which is removed during gutting. White fish are further sub-divided into:
- Round White Fish
Examples include cod, haddock, hake and pollock
- Flat White Fish
Examples include plaice, lemon sole, brill, turbot, black sole are common examples of this category
- Cartilaginous Fish
Ray, rock salmon and shark are examples
Oil-rich fish are so called because the oils are distributed throughout the flesh of the fish. Mackerel, herring, salmon and trout are common examples.
Occasionally you will find fish classified in a different way: Demersal and Pelagic Fish. Demersal fish are those which live on or near the sea bed. Round and flat white fish fall into this category. Pelagic fish swim in mid-waters or near the surface. Oil-rich fish such as mackerel, herring and tuna are common examples.
Shellfish are broadly divided into two main categories: Molluscs and Crustaceans.
Molluscs can be divided into three categories:
- Uni-valve Molluscs
Uni-valve molluscs are those with one shell – periwinkle and whelks.
- Bi-valve Molluscs
Bi-valve molluscs are those with two shells hinged at one end – mussels, oysters and scallops are good examples.
This type of shellfish has no outer shell, but just a single internal one called a pen. Examples include squid and cuttlefish.
Crustaceans are more mobile creatures with hard segmented shells and flexible joints. Examples include prawns, shrimp, crab and lobster.