CRUSTACEANS SCIENCE
Included in the big shellfish family are crustaceans that don't really look like fish, and are actually related to insects (just look at their shells and legs and you see what I mean). Shrimps or prawns, crayfish, crabs, and lobsters are the most common crustaceans on our dinner table. They have five pair of legs, one of which in some species develops into more gigantic claws. The forward part of the body includes the head, which is actually fused with the trunk and equipped with a pair of eyes, antennas, and the legs and claws. The other part of the body is basically the part that swims, and can be called abdomen. It includes muscles that are able to move the rear "fins" (or shall we call them plates?) as the crustacean swims. One exception is the crab that usually doesn't swim and it has a big head instead of a long abdomen.
If you go to purchase some crustacean food you may notice that they are sold either alive or cooked. This is simply because they spoil extremely quickly and thus have to be cooked directly after they've been killed. What causes the trouble is their inner organ that normally secretes enzymes that digest their own food. When a crustacean dies, these enzymes become out of control and start to break down the very meat and inner parts of the animal. In other words, make sure to cook your lobster fresh or to buy it cooked. One word about shrimps though: they can be sold with their digestive organ removed, so they can be kept longer. Nevertheless, the quality will still deteriorate if you wait too long before eating them. When you purchase a crustacean you can take a sniff at it and see if it smells ammonia or disgusting in some way - don't buy it if it does!
The quality of the meat depends on several other factors. One of them is molting - the time when the animal replaces its old cuticle/shell with a new one. During this period, its content of meat is lower and it can become very watery. Such crustaceans are of course not good to eat. The trick here is to catch an animal that is not "off-season", and this varies depending on where you live and what kind of animal you are looking for. Ask the professional fishmongers at your place for more advice.
Cooking live animals can wake up some ethical feelings in us. Usually chefs don't care much about it since they've been told that these animals can't feel any pain due to lack of a developed nervous system. However, noone really knows the truth. To walk around this problem, you can put the animal to deep sleep in an iced salt water for about half an hour, and then put it directly into the boiling water.
When cooking a crustacean meat, the temperature has to be hot and cooking must be done quickly. No oven baking in 150 C here! The reason is that the digestive enzymes in these animals need to be killed by heat instantly, and that can only be done with fast and high heat. Boiling is the fastest way to go! The general taste of a correctly prepared crustacean meat is a sweet, slightly nutty flavor - no strange odors or off-smells. If the heat transfer to the meat is insufficient, the meat may become mushy since the enzymes will become overactive in moderate heat. You should strive for a firm, sweet, tasty meat, and it should be achievable by simple boiling in water.