Fecundity and ovarian cycles of the Antarctic krill Euphausia superba (Crustacea, Euphausiacea)

The fecundity and ovarian cycles of Euphausia superba were studied using three approaches: (i) counting ovarian eggs at several stages of maturity; (ii) counting eggs spawned by individual animals in the laboratory; and (iii) observing the time sequence of ovarian changes by sequential sampling of a laboratory-maintained population. Ovarian egg counts show that the number of eggs per female is directly proportional to body length and inversely proportional to the stage of maturity. Observations of laboratory-maintained animals indicate that spawning is biphasic, occurring in two closely spaced bursts. Maximum total yearly brood size for females 30–50 mm in length is estimated to be approximately 2200–8800 eggs and is directly proportional to body length. After spawning is complete, the ovary reorganizes and reverts to a juvenile appearance within 6 weeks. Reorganization is followed by a prolonged reproductive diapause.