As part two of a series of three columns on shellfish, this one will continue to focus on crustaceans. If you missed my previous column on crab and lobster, please e-mail me at dez@ chefdez.com and I will be more than happy to send it to you.

Crustacean is the grouping that represents crabs, lobsters, shrimp, crayfish, etc. They are all more "creature like" than mollusks (the other shellfish category that will be my focus in the third instalment) because of their visible legs and eyes.

They are usually thought of as only living in saltwater, which is true for the most part, but there are some forms of crayfish, crab and shrimp that also inhabit bodies of fresh water. Lake of the Woods in Kenora, Ont., where we vacation quite frequently, is a perfect example of this. There are many crayfish to be found and some fishers focus solely on these for their catch of the day.

The availability of prawns and shrimp is much more common than crayfish. Rarely available live, the markets near the coast will have prawns and shrimp available fresh (not previously frozen). However, elsewhere they are usually purchased either frozen or thawed from frozen. Small shrimp are also available in cans.

Prawns and shrimp as we know them in the market are actually only the tails of these creatures. Some prawns are available with the legs and shell still attached, but rarer are some larger varieties sold in whole form, eyes and all.

When purchasing frozen, there are many options and you will need to take into account how you plan to serve them when making your selection. Very small shrimp, whether frozen, thawed or canned, are always sold pre-cooked, but with larger prawns one also has the option of purchasing them raw. Frozen cooked prawns should be purchased for recipes that require little or no cooking, since they are already cooked. Overcooked prawns are very rubbery and less flavourful. Examples of applications for cooked prawns would be for a salad, shrimp cocktail, or for adding at the end of a cooked dish. Proper thawing of your prawns is recommended to prevent bacteria growth.

Whether cooked or raw, the recommended procedure for thawing them is in the refrigerator over a period of 24 hours. This is a gradual thaw that keeps them in a safe temperature storage zone. If you are in a hurry, then a water thaw can be acceptable as a second choice.

This is done by putting the frozen prawns in a bowl in the sink. Fill the bowl with cold water and continue to run a slow stream of cold tap water into the bowl.

The water level will obviously overflow so make sure the drain is open. Keep running the stream of cold water until the prawns are thawed, approximately 15 to 20 minutes depending on their size.

Raw prawns purchased fresh, frozen or thawed obviously need to be cooked, but one should never overcook any shellfish because it will become rubbery. They should only be cooked until they just turn pink for optimal flavour and texture, and should be served immediately. Raw prawns are available peeled or unpeeled, with or without tails, and de-veined or not. Deveining of larger prawns should always be done.

The "vein" is the long dark intestine embedded along the top length of the prawn. If the prawns you have purchased are not deveined this can be easily performed by running a knife blade along this line until it is exposed. It can then be simply pulled or scraped out.

Prawns that still have their shell on, but have already been deveined, are frequently called "zipperbacks." These are perfect when you want to serve prawns as a finger food so your guests can peel them as they eat - aptly called "peel and eats."

DEAR CHEF DEZ:

"I heard someone referring to prawns as a 20, 25. What does this mean?"

Rachel T. Airdrie, AB

DEAR RACHEL:

This is referring to their size. A 20/25 prawn is very large. It means that there are approximately 20 to 25 prawns per pound. Therefore, prawns considered to be 32/36 would be much smaller, as there would be an average of 32 to 36 per pound.

. Chef Dez is a food columnist, culinary instructor and cooking show performer. Visit him at www.chefdez. com. Send your food or cooking questions to dez@ chefdez.com.