They're mostly shrimps but there are crabs and crayfish. Crayfish and crabs are not advisable to be mixed with fish. They will often eat and attack your fish and crabs are mostly brackish water.
If you want shrimps, there are cherry shrimps, Amano shrimps and bamboo shrimps.:thumbsup: They will not do well in soft water however as that makes their shells soft leaving them vulnerable to predation.
Unless you have a spare tank which has no fish in it, you can't keep crayfish.
Feed them anything else you give them. I'd try to setup a breeding tank for guppies and put some guppy fry in the crayfish tank for the crayfish to eat. Just add more foods that you usually give to the fish. No veggies though as they're not vegetarians.
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