The colour of a whole fish should be fairly uniform all over.
White patches on a fish are ‘burn’ marks, a sign of poor handling practices.
The eyes should be clear and transparent, or glassy, not overly ‘milky’ or cloudy.
Some fish from deep water may have air in their eyeballs, but overall, still fairly clear.
The gills should be red, not white or light pink.
When cut open, the gut cavity and contents should be firm and bright.
It should have a clean, salty, smell of organs.
The smell of a fish should be a clean salty, and only slightly fishy smell.