ON MATING BEHAVIOR OF ERIOCHEIR JAPONICA DE HAAN

Abstract

Eriocheir japonica mates during the period from the middle of October to the latter part of March and the peak of mating period is from the middle of January to that of February. The mating occus in the inter tidal zone of the neap tide. This crabs usually chose a region nearer the full tide line as a mating place. The mating time is during the tide rising. The crabs showing sexual behavior are more than 3.9cm in carapace width and the smaller crabs which are less than 3.9 cm in carapace width passes the winter in the river. This species changes its nature a few days after having reached the tidal zone and losts its nocternal disposition and comes to behave to the rhythum of an ebb and flow even in the day time. The crabs chose the partners by snipping one another. The opposite sex is recognizd by the degree of the intensity of snipping back. The male crabs living in the river have the second pleopods, but lost them when these crabs come down to the tidal zone for mating. In the laboratory the mating behavior of Eriocheir japonica easily can be observed, by keeping the male and female crabs obtained from the inter tidal zone in aquariums separately, in which 25-30 % sea water is preserved about a week befor pairing. The mating occurs in 25-30 % sea water, in pure sea water and also in fresh water.