17 Dec 2003

I Have Crabs!

Dear Blue Lobster:

I was recently given 3 small crabs that look very much like the larger ones that people eat but these are smaller than a quarter around including the legs. I have never seen anything like them and would like to know how to care for them. They are not hermit crabs. They stay in water like a fish and have no sea shells attached to them. They were purchesed from a pet store so im guessing someone knows about them.

Dear Gentle Sir:

These crustaceans that you have are female fiddler crabs (Uca spp.). I find it curious that the pet store sold these crabs without some sort of label, but the description you provide indicates this gentle decapod. Fiddler crabs can be fun, but here are some rules of thumb to keep in mind while you care for them.

  1. Multiple females are okay, multiple males are a bad idea. Fiddler crabs live in large loose-knit groups called colonies that may number in the thousands. Within each colony are smaller groups called clutches that usually number no more than 12. The group consists of several females of various ages and one dominant male. Immature males may also be part of the group, but generally males will not tolerate other males of breeding age. This social structure holds true in your tank as well as a beach, so feel free to add females to a group but never more than one male. Just because the pet stores stock many males and females together does not mean you should. Ever notice how many males are missing legs? Wonder why no longer.

  2. Much like crayfish, fiddler crabs can breathe air, but unlike crayfish, fiddler crabs must breathe air occasionally. Filling a tank to the top isn't the way to go, so make sure you have plenty of rocks and supports where the crabs can emerge from the water. Also make sure that each fiddler crab has at least two and a half gallons to themselves. Keep the tank temp stays around 76 degrees at all times, and use bright fluorescent lights that mimic natural sunlight. Aquarium conditions are important for the health and longevity of your fiddlers!

  3. Fiddler crabs prefer live food over dried food. Fiddler crabs don't have the largest mouth parts, but a small earthworm or maggot will fit nicely down their gullets. If you can't feed the fiddlers live food all of the time, try frozen blood worms. The fiddler crabs will benefit from the fresh nutrients and be healthier for it. A steady diet of dried pellet food will result in sluggish, lethargic crabs, so these pellets should only be used to add variety to the diet and not as a staple food source. Also make sure some sort of soft water vegetation is available for them to munch on.

  4. Music is important in the life of a fiddler crab. During feeding Chopin or Brahms are appropriate, as the peaceful soothing melodies aid digestion. During the night even slower works are favored as they forage quietly on the tank bottom for leftovers from earlier and groom themselves in the darkness. During mating season the males love to wave their oversized claw around to the works of Wagner and Mozart. The higher frequencies are not so important as the lower ones are, so placing the sub-woofer directly under the tank usually achieves the best results. Your fiddlers will thank you for the music with increased activity and vibrant colors. Don't neglect this aspect of your new pets!

Don't forget to read up on these wonderful creatures both online and at your local library! They can provide hours and hours of entertainment for the whole family as they share their private crustacean world with you through the glass of the aquarium tank!

16 Dec 2003

Craw-Mamma Questions

Dear Blue Lobster:

we have a 36 gallon tank with 1 blue crayfish and 1 red crayfish and some other misc fish. red (her) and blue (him) have mated many times lately and weve noticed eggs on her underside. she has made her nest in a cave area and she hasent been out in almost 2 weeks. she is also now turning green. she doesnt look fussy so we dont think its moss... but im concerned it will kill her. is this normal ? should we force her out and remove this structure so she nests in an open area with better water circulation ? your help is greatly needed...

Dear Gentle Sir:

Firstly, let us discuss identification of your crays. It seems that the red female cray is a procambarus clarkii, commonly known as the Red Swamp Crayfish, while the blue male is a procambarus alleni, commonly referred to as the Blue Lobster. These species are found in the American Deep South swamps and ponds and are easy to breed and maintain, hence their commercial distribution as pets around the world.

Your Red Swamp Cray is what we call in berry, reffering to the berry-like mass of eggs under her tail. She is indeed pregnant and in just a few short days your tank will be crawling with hundreds of tiny baby crayfish (called craybies by professionals) of the hybrid type procambarus alleni × clarkii. Since this is a coupling of a Blue Lobster and a Red Swamp Cray, we can expect the craybies to be purple, which is a rarity in the crustacean world.

Your concern for the craybies very valid. During berry, the female cray secretes a hormone into the water that will keep the male at bay. After hatching, the mother will care for her offspring, letting them ride under her tail; however, after this period the mother and any other crays will consider the hatchlings as food. It is time to remove all other creatures from the tank lest you risk them being eaten. The world of the crayfish is a savage one filled with hunger, violence, and death.

As for the green coloration of the Red Swamp Cray, the most likely explanation is that the cray is simply changing colors. The exoskeleton itself is semi-transparent and a cray's coloration actually comes from its muscles and blood. Cray coloration changes for every occasion, including pregnancy, mating, and dying. A crayfish's color may change over life too, and water chemistry factors in as well. Assuming she doesn't seem agitated and the eggs aren't shriveling, she will be fine.

Good luck and enjoy your thousands-strong brood of hungry craybies!