OVARIAN DEVELOPMENT AND SEXUAL MATURITY STAGING IN ANTARCTIC KRILL, EUPHAUSIA-SUPERBA DANA (EUPHAUSIACEA)

Several lines of evidence suggest that reproductive development in Antarctic krill is not a simple stepwise process. We present a new method for staging sexual development of female krill, and a key which can be used for live animals and Formalin-fixed samples. The key takes into account female general appearance, thelycum development, ovarian morphology, and developmental steps of changes in the ovarian cells. This staging method is based on the results of a histological study of ovarian development, but the use of the key itself involves only simple observations and rapid execution of a squash from a piece of the ovary. The reproductive cycle of krill is divided into 10 stages: 8 stages for ovarian development leading to egg production, and 2 stages for sexual regression and reorganization after spawning periods. We believe that such a method could be useful for predicting spawning events and their timing for Antarctic krill, and for a better estimation of fecundity and related energy requirements. Similar keys devised for other euphausiids and free-spawning pelagic crustaceans will allow comparisons among different reproductive strategies.