Gonad history of the Antarctic krill Euphausia superba dana during its breeding season

Summary

Krill were collected in January–February 1986, north of Prydz Bay, Antarctica. Their gonad history was reconstructed from observations of live krill maintained on board ship, and subsequently fixed for histology. Size, molt-stage and external stage of sexual maturity were recorded for each individual. Males appeared to be continually producing sperm. Among mature females, the ovaries had various compositional zones: germinal zones and 1 to 3 batches of maturing oocytes (in primary or secondary vitellogenesis) were simultaneously present. Therefore a female can successively lay at least three batches of eggs, at short intervals corresponding to the duration of one cycle of secondary vitellogenesis. Most post-spawn females had reverted to juvenile status (ovary reduced to germinal zones). Large females were found with an already reorganized ovary with numerous secondary oogonia and very young oocytes. It is concluded that oogenesis occurs before the winter rest and that only the vitellogenetic cycles are postponned until the next reproductive season.