The Influence of Vitamin B12 Deficiency on the Reproduction of Daphnia Pulex Leydig (Cladocera)

When maintained in media containing 5 jig/l of cobalt and fed 6 x 106 cells of Chlamydomonas reinhardti plus 6 x 106 cells of Nitzschia frustulum every 56 h, at brood/ecdysis/ transfer, Daphnia pulex requires extraneous vitamin B,, for normal reproduction. The rate of brood production increases with concentration of B,2 in the media (0.375 �g/1 < 0.75 Agll < 1.5 wg/1). The number of progeny is highest at 0.75-1.0 �g!l. Most animals deprived of B,2 appear normal but none produce reproductively viable progeny. When 1.0 AgIl of B,, is added directly to the MS animal medium, an average of 17 broods per life-span is produced.