I’ve seen people poke, prod, and even sniff their fish (please don’t do that). The most reliable test is the fork test: insert a fork into the thickest part of the fillet and twist gently. If the flesh separates into flakes and looks opaque, you’re done.
Another trick: use an instant-read thermometer. Fish is perfectly cooked at 145°F (63°C) in the center. I keep one in my kitchen drawer, and it has saved me from serving more “salmon sushi” than I care to admit.
Final side comment: If you’re feeling brave, remember that frozen fish can handle a little extra time better than thawed fish. So if you’re distracted by Netflix, no stress—just add a couple of minutes and check again. You’ve got this.