In part one of my article on freshwater crustaceans, I covered general decapod biology and aquarium care, with a look at the different species of shrimps that are available in the hobby. The other freshwater decapods kept by aquarists are crayfishes and crabs. Although somewhat
less popular than shrimp, crayfishes and crabs are readily
available and often do best in dedicated setups.
Crayfish are typically considered keystone species to the
biological communities in which they belong because of their
feeding and burrowing behaviors. They are interesting animals
with gills that keep their shape out of water. Since the gills are
surrounded by the shell-like exoskeleton of the crayfish, they can
be kept moist even on dry land. This allows the crayfish to leave
water for at least short periods of time.
Being able to move on land confers many advantages to crayfish:
They can have access to more resources, seek out better habitats if
their current one becomes unsuitable, and disperse more widely. It
also allows them to enter many different types of habitats. A few
crayfish species inhabit brackish waters, and several are found in
semiterrestrial and subterranean habitats.
Taxonomically speaking, crayfish are members of the infraorder
Astacidea, which includes lobsters as well. Lobsters are an
exclusively marine group, whereas crayfish are known to inhabit
only fresh (and in some cases brackish) waters. Though details
about this group’s origin remain unclear, it seems that all members
share a common freshwater ancestor. This contrasts with many
other groups of aquatic animals, in which freshwater forms derive
from marine ancestors.
The crayfish are a large group that includes about 450 species,
with the greatest diversity being found in Australia and North