From the discussion above I find 3 ideas very useful for understanding the trouble with eating shellfish. 1) Shell fish is the pig of the sea 2) lobster is a marine version of corkroach 3) Shell fish are scavengers of the sea eating mostly the dirt and dead animals on the sea floor. Come to think of it their diet might include defecations of other sea creatures.
Also, I find very valuable, is the esoteric observation: that whatever we eat will effect us. If we eat peaceful animals (cows goats) we can establish peace and calm within ourselves. If we eat creatures that consume toxins, dead animals, bacteria, defecation, we inculcate chaos and spiritual sickness with in ourselves.
We absorb not just the nutrients from the food, but we also absorb the esoteric, occultic properties in the food source.