EARLY DEVELOPMENT OF THE BALONS RUFF, GYMNOCEPHALUS BALONI HOLCIK ANDHENSEL, 1974

The early ontogeny of Balon's ruff, Gymnocephalus baloni was examined according to the theory of saltatory ontogeny. The developmental steps , growth, and plastic characters are described and discussed The eggs of Balon's ruff are small (after activation, 1.12 mm diameter) and ver y adhesive. Embryonic development lasted 7 days and larval development 25 days (32 days total), with water temperature ranging from 16-degre es-C to 52.7-degrees-C (average 19.6-degrees-C). Embryos hatched from 3 to 5 days after activation. The simple embryonic circulatory system probably reflects the high oxygen requirements of the embryos, which d evelop very near to lotic enviroment. The larval period is characteris ed by changes that improve the manoeverability of the larvae. At the s tart of the juvenile period several plastic characters (minimum body d epth, head length, preorbital distance and eye diameter) considerably change their values, attaining the level corresponding to adults.