If you want to know whether fish is fresh, there are a number of signs you should look out for. Fresh fish has bright, convex (bulging) eyes with a dark pupil. The flesh of a fresh fish is translucent (almost transparent), but as it ages it gets darker and more opaque (you cannot see through it).

A fresh and sound fish shows the following typical characteristics:

• The gills are bright, usually closed and have no abnormal odour.
• The eyes are prominent with a transparent cornea (the outer surface of the eye).
• The scales are difficult to remove.
• The skin is free from malodorous (bad-smelling) slime and is not discoloured.
• The flesh is firm, the body stiff and the tail rigid.
• The carcass (body) sinks in water.

A fish that is not fresh and is starting to rot shows changes in all these signs. For example, the gills may be open and discoloured, and the skin slimy and malodorous. The eyes are opaque and sunken, the scales can be removed easily and the carcass floats in water. The flesh falls easily from the bones and is easily broken up.