Fish that are fresh can be easily identified by noting the following qualities.
The skin looks bright, moist and shiny. The scales should be firmly attached to the skin.
The skin on stale fish may shows signs of wrinkling and shrinking away from the flesh.
The eyes of a freshly caught fish will be convex, the pupil black and the cornea translucent. The eyes should be bright, clear and bulging and not sunken.
The gills of freshly caught fish are bright red, but as the blood in them oxidises they rapidly turn brownish and any mucus on them turns opaque.
If fish is split along the backbone and lifted, the bone should stick firmly to the flesh. If the bone separates easily, the fish is stale.
The surface should be free of dirt and slime.
The flesh should be firm to touch with no traces of browning or drying around the edges.
A fish having odour indicates deterioration due to oxidation of polyunsaturated fat and bacterial growth, Rancidity is revealed by yellowish spots on the surface.
Rancidity can be recognised by sour taste, uncharacteristic of fresh fish.
