What factor is crucial in determining the proper cooking of fish?

The proper cooking of fish is primarily determined by its texture and flakiness. When fish is cooked correctly, it undergoes changes in its protein structure, making it tender and easier to separate with a fork. A well-cooked fish will flake easily when tested, indicating that it is done. The texture becomes firm yet moist, which is an important aspect of its quality.

While aroma, color, and size can offer some clues about fish freshness or even cooking status, they do not provide as reliable an indicator as texture and flakiness. The aroma of fish might suggest freshness but is not a definitive measure of doneness. Color can vary greatly among different types of fish and may not reflect proper cooking, as it depends on various factors including species and cooking method. Size does play a role in cooking times, but alone it does not determine if the fish has reached its ideal texture and flakiness, which should be the primary focus when assessing if fish is properly cooked.