SIZE AND MATURITY STAGE OBSERVATIONS OF THE DEEP-SEA ISOPOD BATHYNOMUS-DOEDERLEINI ORTMANN, 1894 (FLABELLIFERA, CIROLANIDAE), IN EASTERN TAIWAN

Seven collections of the deep-sea isopod Bathynomus doederleini Ortman n were made, using baited traps in waters of eastern Taiwan between 30 0-500-m depth from June 1990 to February 1992. Body length, developmen tal stage, and gonad development were recorded for individuals. indivi duals (N = 2,007) ranged from 28-138 mm in length with seasonal variat ion in size distribution. Recruitment (manca stage) was high between M ay and September. Mature individuals with fully developed secondary se x organs represented 3.6% of all the samples collected. Males, with pe nes, could be identified at a smaller size (body length 50 mm) than fe males (88 mm), which had vestigial or developed oostegites. Eight of 1 0 mature males, i.e., with appendices masculinae, all larger than 100 mm, had testes. A higher frequency (>73%) of large females (> 100 mm) possessed developed ovaries than small females(13% between 88-100 mm). Among egg-carrying females no correlation was found between size and fecundity. No seasonality of reproductive activity was observed. The s ex ratio was significantly different from 1:1 among large individuals (>95 mm), and was biased toward females.