Seasonal change in molting activity of juvenile beni-zuwai crab Chionoecetes japonicus revealed by a rearing experiment using deep-sea water

Abstract

In order to elucidate the molting activity of juvenile beni-zuwai crab Chionoecetes japonicus, a rearing experiment was conducted using running deep-sea water from Toyama Bay, which was maintained at a temperature of 0.7±0.1°C (median±interquartile range). The molting date for individuals was examined until January 2005 for 167 crabs at 3rd-8th instars (carapace width: 5-39 mm), which were collected from Toyama Bay in January and February 2003 and January 2004. Although each molting activity for the 4th-7th instars lasted for 7-11 months, the peak of molting was limited seasonally and was different between instars (4th instar, August-September; 5th instar, March-April; 6th instar, October-January; 7th instar, August-September). The midpoint date of the molting season was defined as total of the base point date and the median of the days from the base point date to each molting date, and these were calculated as August 26th, April 2nd, November 23rd, September 9th from 4th to 7th instar, respectively. These findings suggest that the duration (intermolt period) at each instar from 5th to 7th instar is about 7.3, 8.0, and 9.7 months long, respectively.