There are more than 1,300 species of freshwater crabs and, as such, there is no one diet consistent to all of them. However, most are omnivores and scavengers.
Some freshwater crab species eat dead leaves and algae, while a small number of species are carnivorous. Platythelphusa armata, for example, lives almost exclusively on snails found in Lake Tanganyika. However, most freshwater crabs are not particular about what they eat, and many subsist on the detritus that accumulates at the bottom of rivers, lakes or aquariums.
Freshwater crabs generally live in tropical and subtropical climates, and while many live around bodies of water, some live in caves or even the boles of trees. They usually play integral roles in their ecosystems, with many species serving as a source of food for other animals and as a way of determining water quality for scientists due to their dependency on clean water. Because many species have such specialized habitats, freshwater crabs are also largely endangered; for instance, 40 of the 50 species native to Sri Lanka are threatened. Semi-terrestrial species that require both land and water to live on are most commonly in danger.
Few freshwater crabs are available as pets. Even the mini crab, a kind of fiddler crab commonly sold in pet stores, requires brackish water, meaning it needs at least some salt in its environment. Many species sold in pet stores also require some amount of land in their aquarium. In terms of diet, mini crabs eat bloodworms and brine shrimp, although they will also consume any uneaten fish food that gathers at the bottom.