Ecological and morphological studies on the japanese fresh water crab geothelphusa dehaani

Yamaguchi, T.; Takamatsu, Y.

Kumamoto Journal of Science Biology 15(1): 1-27


Accession: 005209628

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Ecological and morphological studies on the freshwater crab, G. dehaani, were carried out mainly on the population at Kikuchi-Keikoku, Central Kyushu [Japan]. This crab is an almost totally nocturnal, prefers clear non-polluted water and is amphibious. Young-crab-carrying females were found in the pools in the stream during from the middle of Aug. to the beginning of Oct. The average number of young crabs in a clutch was 38. The growth and age structure of G. dehaani was estimated from the monthly change and shifting of peaks appearing in the size frequency histograms. After hatching, young crabs do not molt until June of the following year. Molting is repeated 2 or 3 times a year and part of the crabs mature in the 4th year. Almost all of the crabs collected in Central Kyushu showed the same type of coloration. Cheliped asymmetry develops in the males and right-handedness is dominant. Determination of caloric values on body, hepatopancreas and ovary was carried out on the samples of May and Sept. The samples of May always showed a higher value than those of Sept. A montly change of the gonad index was found in the female; it was high before the reproductive season, but low during the season. The change was less conspicuous in the hepatopancreas index. In the male, no large monthly change of gonad index was found. The existence of 2 groups of females by time of egg-laying was assumed. The females of the 1st group lay eggs in the early half of the reproductive period, and those of the 2nd group lay eggs in the latter half. Total caloric content indicates that the adult female consumes a large amount of energy during reproductive activities. In the male, the difference was negligible and the content was almost the same as that of females at the end of the season.