Take with itself in shop a toothpick. Choosing fish, make a puncture in the field of a paunch. If the product has started to spoil, you will feel at once an unpleasant smell.
Pay attention to gills: if they pale, fish obviously not the first freshness and if from under them gives sour, fish has precisely deteriorated.
When buy slabosolenuju a trout in vacuum packing, prefer the whole piece. Under appetizing sandwich-type slices, there can be scraps which put there for weight.