All

Evenly frozen, no ice crystals

Ice crystals built up within the gaps in the flesh

Raised edges and ice crystals between muscle segments indicate that the original product was frozen slowly, not in prime condition or that it has been thawed and refrozen.

Colour

Bright and glossy, particularly cut surfaces

Slightly dull and discoloured (bleached, yellow, brown or black spots)
Slightly dried out edges; some cottony patches

Properly frozen seafood will retain much of its colour. Bruising can cause black discolouration.
Dehydration can result in freezer burn—bleached spots, papery or cottony edges and a dry texture.
Oxidation causes the flesh to turn yellow and then brown.
Dehydration and oxidation are not health hazards but do indicate poor eating quality.

Packaging

Tight wrapping, moisture-proof wrapping, undamaged; glazing intact

Slightly dull, "sticky" appearance; irregular darkening; drying at edges

Generally, damaged packaging indicates rough handling and the entry of air. It is advisable not to buy frozen seafood that is poorly packed. Ice build-up inside a package indicates temperature fluctuation.

Clean, fresh smell; virtually odourless

A distinct "refrigerator" smell

An odour in frozen seafood suggests quality problems, and a closer inspection is required. The colder the seafood, the less odour it emits.

Hard

Signs of partial thawing (soft edges and a build-up of moisture)