Freezing fish is a procedure and most people get it wrong. Some species of fish do well in a freezer (like kingfish), while others just don’t like it and go mushy when defrosted (like threadfin salmon).
You need to know which species freeze well, and what to avoid, so the rule (generally) is that firm fillets or whole fish like snapper freeze very well. Softer flesh fish not so much, but your local fishmonger will know.
Buying fish should be done from a fishmonger, who will know where the fish came from, how sustainable it is, how it was caught, and how to cook and store it. Make best friends with these people! They know stuff.
How to freeze fish
When the fillets are ready to be frozen, put them into freezer bags and dip the bag into a sink full of cold water. This removes the air from the bag. Seal the bag around the fish to seal it.
Why do we want no air? It is the cause of freezer burn and causes your fish to become unusable faster.
Freezing whole fish
If you are freezing whole fish, don’t take the scales off before freezing, as it protects them. This can cause some problems with descaling after defrosting though, so you’ll need to figure this one out depending on the fish and your circumstances (like how soon will you be eating the fish?).
Vacuum seal your fish
A food saver is an electronic device that vacuum seals your food, and they are an excellent way to keep fish frozen. If you are serious about your fish, you may want to invest in one.
Talk to your fishmonger about your fish and the best way to store and use it.