How to Care for a Fire Urchin

Fire urchins are one type of the more general sea urchin family, Echinoidea. While they range in color from bright red to blue or purple with red spines, their main similarities are a flexible body and poisonous spines that can cause serious injury to humans. They are generally found in shallow, warm sea water and are mainly active at night. Fire urchins are in general low-maintenance aquarium residents, but they should be watched carefully for signs of illness, which include drooping spines.

  1. Feeding

    • Like most urchins, fire urchins are bottom feeders and generally live on a diet of algae, seaweed and tank detritus. However, they do like meat occasionally and because fire urchins are far more mobile than many of their relatives, they may come across some of your slower tank denizens. Feed them some meat on occasion, about once a week, to keep them happy. Stanford University's website recommends feeding urchins carrots or a "cookie" made with carrots, eggs and agar. Lettuce or cabbage may also make a substitute for algae and seaweed.

    Water Temperature

    • Fire urchins prefer warm water, in the range of 70 to 82 degrees Fahrenheit. To be safe, keep the urchin in its plastic bag when you bring it home and allow it to float on the top of the tank for an hour to adapt to the water temperature. If it is introduced to colder water than it is used to abruptly, it may go into shock and die. While some urchins can survive in cold water, fire urchins cannot.

    Water Quality

    • Fire urchins, like all urchins, are highly sensitive to water quality. In fact, urchins are considered indicator species for detecting water pollution, as they react very rapidly, with their spines drooping and a tendency to spawn spontaneously. Water containing urchins should be fresh sea water or, if using an artificial salt water, have a salinity of between 1.020 and 1.026. It should also be filtered regularly to remove waste material, and the bottom of the tank should be cleaned regularly as well. The tank should be well aerated as well; fire urchins are sensitive to oxygen content.

    Environment

    • Fire urchins are highly mobile and will climb over rock, coral and other tank fixtures, possibly dislodging a heavy piece that may crush the urchin. Make sure that all fixtures are stable and if necessary anchored. Fire urchins are also sensitive to metal poisoning, particularly from copper. Make sure there are no metallic pieces in the tank that may corrode and harm the urchins. While the fire urchin's spines provide it protection against predators, they are not effective against some, including starfish, crabs and some eels. Some fish develop a strategy of blowing water under an urchin, allowing it to attack the less-protected underside of the animal.