Tilapia is cooked through when it is no longer translucent and the fish has a tender texture and flakes easily. The outside should be golden brown and look crispy if it is breaded. If it's cooked too long, the fish will be rubbery in texture instead of buttery. If you're really not sure, you can use a meat thermometer to see if the fish has reached a safe internal temperature of 145°F per the USDA.