The occurence of the crustacean Branchinecta gaini was observed in the fresh-water ponds on King George Island. Morphological structure of the following developmental stages was described: nauplius, metanauplius, adult males, adult females, and gravid females with egg-sacs filled with eggs. The active phase of the life cycle of this species lasts 6 months (November-May). During that time one generation of Branchinecta develops. The reproductive season lasts from January until the freezing of the ponds.