Abstract
The population structure, relative growth and reproduction of the fiddler crab, Uca arcuata (De Haan) were studied at Ohno River, Central Kyushu, Japan. The minimum size of ovigerous crabs was 19.4 mm CW. The largest size was 36.8 mm CW in males and 33.6 mm CW in females. Three and a half year rearing was conducted in the laboratory. Newly settled crabs grow to 19 mm CW by the end of next year, but females deposit eggs in the following year. The crabs reared in the laboratory grew to a maximum size of 32.5 mm CW in males and 29.3 mm CW in females. The size distribution and the results of rearing suggest that U. arcuata survives more than five years. Males were predominant in number; sex ratio was 1.36:1.00. Ovigerous females appeared from the last third of May to the last third of August. It is likely that females deposit eggs two or more times during the reproductive period. The relationship between egg number (Y) and crab size (X) is: Y=5721.4X-93702. Ovigerous females feed on the surface. There is an inverse relationship between the gonad and hepatopancreas indices suggesting that substances are shifted from the hepatopancreas to the ovary. The percentage of the large cheliped to total body weight increased with the crab size, reaching 40%.
