The goal when freezing food is to keep the moisture in and the O2 out. Surrounding the fillet with ice is an acceptable "quick and dirty" way to do this, but a vacuum seal pouch is better. The longer it takes to freeze the fillet, the larger the ice crystals that will develop. The larger ice crystals do more damage to the cells of the fillet, that's why commercial freezing is done at super low temps (flash freezing). By surrounding the fillet with water you increase freezing time and therefore increase damage to the cell walls.

Another disadvantage of freezing in an ice block is the increased time to thaw the fillets. Besides being less convenient, the longer thaw time will keep the fillet in contact with water longer. The freezing process makes the fillet more permeable so soaking in water will leach out more flavor. Imitation crabmeat is produced by submerging fish fillets in very cold water because this process slowly removes the fishes inherent flavor.

Vacuum packaging is the best way to store refrigerated or frozen flesh, but it requires expensive equipment. If you're not too fussy about taste/texture then traditional techniques are fine. If you want to go completely over the top you can vacuum pack your fillets and flash freeze them with dry ice! \:o

I'm not certain about all of the above statements, but there you go.


Fish freezing links:

http://www.uga.edu/nchfp/how/freeze/fish.html

http://www.ag.ndsu.edu/pubs/yf/foods/fnw615.htm

http://www.uaf.edu/ces/publications/freepubs/FNH-00222.html

http://www.continentalcarbonic.com/dryice/freezingfish.php