Is it possible to identify the quality of fish after cooking the fish? One know that a fish is fresh if the fish eye is clear and bulging and its gills is ought to be red.

However, if the fish is being cut into many slices and the fish head was being removed, it would be very hard to identify if the fish is of good quality (fresh) or poor quality (not fresh).

So, is it possible to say that when cooking a poor quality fish, the outcome is that the fish meat will be quite hard? (I mean like when one bite the cooked fish, it feel like eating a over-cook chicken breast meat.)

or how do I know the fish is good or bad after cooking it? (This is especially true when you eat in some restaurant that you can't see the fish itself)
Old filets of fish will be slimy and have an overly fishy smell. When frozen filets are poorly stored, (refrozen/not flash frozen/stored at improper temperature/too old) they have this texture of eating a sponge that makes me wretch, since the delicate emulsion properties of the flesh have been completely broken down. The moisture can be sucked out and the proteinous membranes chewed on like rough, spongey, dough. If you try to skin them, they sometimes come apart in your hands rather than adhere like tissue from a living organism.

When cooked poorly (burnt to a crisp, overseasoned), it's difficult to tell the difference between fresh and old filets.