Here's How To Stop Overcooking Your Fish
In order to understand how to cook fish so it's not overdone, experts at Exploratorium think you'll probably need to understand the difference between fish and other types of meat.
The next time you pick up a fish fillet, take a closer look and you might notice a distinctive white pattern found between and around the fish's muscles. Those pearly, connective strands are what we know as collagen, which holds thick muscle fibers together. When a piece of fish cooks, its flesh changes from a translucent to opaque; at the same time, the collagen also softens gradually before turning into gelatin.
The same thing happens with other types of meat, but because its muscle fibers are shorter, the process that cooks flesh and transforms collagen happens more quickly in fish, so that if you cooked meat and fish the same way and with the same temperatures, your meat might be well cooked, but you'd be left with a bone-dry, flaky piece of fish.
There is a way to test fish for doneness
When the fish's strands begin to ooze white protein, James Beard-award winning chef Galen Zamarra tells Food & Wine that this is a sure sign that the fish has crossed over from nearly done to overcooked. But Zamarra says it's easy to monitor a piece of fish that's cooking. "A trick that people can use for checking doneness is actually a cake tester, or even a paperclip. You open up the paperclip so it's a nice straight line. When you stick the point into the fish, there should be no resistance," Zamarra says. "If it's not done, you'll start to push it in, and it'll just stop. So, once you can go in and it comes out and there's no resistance, the fish is done."
If you don't trust yourself to keep your fish from overcooking, The Kitchn recommends you cook fish by either poaching or braising. Both methods fall into the moist method of cooking because they rely on a liquid like water or stock to cook the fish through. And because fish is submerged when it is cooked both ways, it isn't likely to dry out. But you'll still need to set your timer so you can retrieve your fish on time, because overcooking a fish by moist cooking will leave you with mushy fish — which could well be worse than ending up with a dried-out fillet.