Laboratory observations on spawning, fecundity and early development of a mesopelagic ostracod, Conchoecia pseudodiscophora, from the Japan Sea

Abstract

Adult females of a halocyprid ostracod, Conchoecia pseudodiscophora, collected from the mesopelagic zone of the Japan Sea in June and September 1990, were fed frozen and freshly killed copepods and maintained in the laboratory to assess brood size, number of broods, the interval between consecutive broods and egg hatchability. A single female released 1 to 10 eggs brood^-1 (mean: 5.9 eggs, N=35), and the intervals between consecutive broods ranged widely, from 2 to 64 d (mean: 31.0d, N=16). As many as four consecutive broods were recorded for two females. Mean hatchability of eggs was 72.7% (N=25), with no apparent relation with the number of consecutive broods and season. Hatching time of eggs was 12 to 15d at 0.5°C. Newly hatched juveniles (Instar I) developed to Instar II in 32d, and to Instar III in 72d, at 0.5°C. Judging from the morphology of appendages. Instars I and II were non-feeding stages. Morphological and dimensional data for eggs and Instars I, II and III obtained in this laboratory experiment were compared with those from field samples. The total number of instars and growth of C. pseudodiscophora are discussed in conjunction with presently available data on halocyprid ostracods.