General Information Freshwater Shrimps, Crayfish (“Lobsters”), and Crabs, also referred to as crustaceans, have gained popularity among aquarists in recent years and more species are now available to the hobby than ever before. They are an interesting addition to aquariums that typically only contain fish. Although some Crabs prefer a small area of exposed driftwood, rock, or other substrate to periodically climb on, they are all bottom-dwelling species. All are either predators or opportunistic scavengers and most are omnivores. Crustaceans are covered with a hard shell (exoskeleton) that they shed as they grow larger. It is typical for inexperienced aquarists to see this discarded exoskeleton on the bottom of the tank and suspect that their Shrimp or Crab has died!