There are many commandments regarding food in the Torah (known to Christians as the Pentateuch). Among them, Jews are commanded not to eat anything which lives in the water, unless it has fins and easily removed scales. Consequently, prawns, as well as shrimp, crabs, calamari, etc., are forbidden. Swordfish and sturgeon have fins but no scales, so Jews don't eat those either. For more information, look in The Bible under Leviticus 11: 9-12 and Deuteronomy 14: 9-10.
Jews who keep kosher don't eat crab because God has forbidden it to us in the Torah. Specifically, it violates the requirement that all sea creatures fit for consumption by Jews must have fins and scales (Deuteronomy ch.14), of which a crab has neither.
prawns eat plankton, tiny creatures in the sea
they eat prawns
no
Yes, they do.
yes
They're a type of crustacean. Copepod (maybe?) but not fish.
Yes, it's safe for dogs to eat prawns or shrimp.
No. Its meat
No, unless it is artificial flavoring. Prawns and other shelfish are not kosher. The only kosher seafood are fish that have both fins and scales.
they eat prawns
yes
Prawn are mostly eaten by fish. They are a great source for bait.