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Friday, May 17, 2002

ANIMAL TRACKER

Long-armed shrimp


* Japanese name: Tenaga-ebi
* Scientific name: Macrobrachium nipponese
* Description: Long-armed shrimp are accurately named. They are crustaceans in the family that includes lobsters and crabs, all of which have 10 pairs of legs. In the long-armed shrimp, the first five pairs are the walking legs, the second five the swimming legs. The second pair of walking legs are much longer than the others, and they are longer in males than in females. The scientific name means "big arms." Also known as giant freshwater prawns, long-armed shrimp grow to around 10 cm long, sometimes more, depending on their diet. Adults sometimes develop a blue-green color, sometimes brown, again depending on diet.
* Where to find them: In rivers and streams in Honshu and northern Kyushu. There are 12 species of long-armed shrimp in Japan, most of them living in the Ryukyu Island group, but three species live in Kyushu and one in Honshu. Some larger species are commercially cultured.
* Food: The larvae eat aquatic insects and their larvae, as well as algae, mollusks, worms, fish and, if scavenging, the feces of fish and other animals. Adults mainly feed on algae.
* Special features: Like all crustaceans, long-armed shrimp have a hard exoskeleton that they must molt in order to grow. Reproduction can only occur between a hard-bodied male and a soft-bodied female. This means males must catch females just after they molt and deposit sperm in a mass beneath the female's swimming legs before her new exoskeleton hardens. Females lay their eggs into the sperm mass, where they are fertilized. The eggs are then drawn into a brood chamber under the female's tail. The mother keeps the eggs clean and aerated by movements of her tail. The eggs hatch after about three weeks. The bigger the female, the more eggs she produces. At high densities, males become territorial; their long arms are useful for fighting.



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