Fiddler crabs are found in muddy marshlands bordering marine bays and surrounding tributaries. These crustaceans are unmistakable in appearance, since the male sports one remarkably large claw, with which he wards off intruders or waves up and down in a fiddling motion to attract a mate. Females do not have the distinctive fiddle claw. The large claws of the male are virtually useless in feeding, which gives the females the advantage (being ambidextrous), as droves of fiddlers move over tidal mud flats in search of bits of algae or decaying marsh plants. The crab scoops sand into its mouth, straining and swallowing the organic matter while forming the remaining sand into pellets which it discards. Normally the right claw is large, but if it is broken off, the left will enlarge and a new small claw will grow on the right one.
Fiddler crabs can be found living in communities in burrows just below the high tide mark. These burrows slant down one foot or more and end in a horizontal room. Fiddlers dig holes by packing wet sand between their legs and pressing it into pellets which they remove. Before each high tide the crabs retreat into their burrows, plugging the opening with sand pellets to keep the water out. In the fall, crabs in colder regions burrow and hibernate, only to emerge by the thousands in spring to renew their frenzied activities.
Fiddler crabs are a lighter color at night than in the daytime. These color changes seem to be related to tidal rhythms as they are darkest when the tide is low. This is also when they are the most active. The color changes are induced by neurosecretory hormones present in the eye stalks. Pigments are contained in chromatophore cells present in the carapace and legs of the crab. These cells, when influenced by the hormone, expand by day causing them to appear darker and contract by night causing them to appear lighter.
To prepare the habitat, place 1 lb. of sand at one end of the aquarium and grade it gradually so that it forms a slope covering 2⁄3 of the aquarium. Fill the other 1⁄3 with either a solution of conditioned water and sea salts or with sea water, depending on the species. Change the water once a week or when it becomes cloudy or foul.
To make conditioned water, use “Water Conditioner”, or simply aerate tap water for 24 hours.
To make “brackish water” (25% sea water), add 1⁄4 cup of sea salts to 2 gallons of conditioned water. Mix thoroughly.
To make sea water, add 1 cup of sea salts to 2 gallons of conditioned water. Mix until completely dissolved.
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