Most packets of frozen mixed seafood do not need to be cooked, but can be defrosted and eaten raw. The key issue, whether you cook them or eat them cold, is that they should be defrosted properly first. Cooking seafood in its frozen state results in a rubbery texture. Putting frozen seafood in a salad or in a mayonnaise sauce would water down the other contents of the dish as they thaw and give a hard gritty texture.
Remove the amount of seafood you want to use from the bag and return the remainder to the freezer. You do not have to cook all the contents of a bag of frozen seafood all at once. However, you may find it difficult to separate out only the portion you want because the contents may have formed a lump. With the bag firmly sealed, swing it vigorously to bash it against a wall. You need to break up the main lump so enough separates. If that doesn’t work, take out the whole lump and cut through it with a serrated knife as though slicing through bread. Do not let all of the contents defrost and then re-freeze the remainder.
Try to break up as much of the lump of seafood as you can, either by stabbing at it with a knife or fork or peeling away segments. The smaller the lumps of seafood are, the quicker the mix will thaw.
Thaw the seafood mix in a covered bowl in the fridge. Leave it at least overnight. When you come to use it, you will find the seafood lies in a pool of water. Tip the contents of the bowl into a colander or sieve before adding it to your recipe. If you can’t wait that long to thaw the seafood, seal it in a plastic bag and then sit it in a large bowl of cold water. Do not use hot water or run it under the tap. If you do, it will not retain its shape,but will more likely partially disintegrate with the ice. You can defrost it in the microwave on a defrost setting. However, do not defrost it all the way through, but take it out of the microwave when it becomes flexible. Let it sit in a covered bowl on a worktop as you prepare and cook your other ingredients.
Every packet of seafood has instructions for use written on it. Read the instructions carefully in case the bag you bought needs special treatment.