Neither of these animals lives in a freshwater aquarium environment. They are creatures of the sea shores, beaches and mangroves.
they eat mole crabs
ThierAunts.
yes
no
they eat freeze dried plankton.
Plants, fish, and sometimes other fiddler crabs.
More likely the opposite, the crab will eat/kill your dragon fish. Plus fiddler crabs do not often reproduce in captivity.
Frozen bloodworms
they eat freeze dried plankton.
They occasionally eat other fiddler crab but are eaten by raccoons and shore birds.
Fiddler crabs should never eat human food. They are not able to digest human food. However, they should be fed crab food or fish food.
the Pokemon named arceus eats it