Summarize this article in one sentence.
Fish is normally sold in plastic bags or another type of plastic wrapping. For tuna steaks and other fish, there's no need to remove the bags when thawing the fish. The tuna steak will still properly thaw when wrapped in the plastic bag. It's very important that you don't leave the tuna steaks out at room temperature in the kitchen or elsewhere in the house. Fish spoils easily and the fridge will thaw the tuna steak while also keeping it cool at the same time. Room temperature defrosting will thaw the outside layers of the tuna steak while the inside layers go bad. Use a thermometer to make sure your fridge is 5C (41F) or cooler. This is the right temperature for defrosting fish. While it might only take the tuna steak a few hours to thaw in the fridge, you want to be sure that it's completely defrosted before using it. By leaving it overnight, you give the tuna steak enough time to properly defrost. Don't leave the tuna steak in the fridge for longer than 24 hours. The longer the fish is in the fridge, the higher the chances of it going bad. Now that you gave your tuna steak the entire night in the fridge to defrost, you can remove it from the fridge. Take the tuna steak from the plastic bag and inspect it to make sure there's no signs of frost or ice.

Summary:
Leave the tuna steak in the packaging to thaw. Place the tuna steak in the fridge. Leave the tuna steak in the fridge overnight. Remove the tuna steak from the fridge the next day.