Early ontogeny of sunbleak

The early development of sunbleak Leucasphis delineatus, from activation of ovum to juvenile, was recorded using both living and preserved materials. Five embryonic steps, one free embryo and five larval steps were identified. Hatching occurred between 73 It 25 min and 85 It 25 min (post-activation); the free embryo period was extremely short in duration (3-16 h). The transition from larva to juvenile occurred in c. 96 days when the fish were fully scaled and the lateral line organ clearly visible. During early development, developmental thresholds were identified between steps, which suggested possible switches in ecology, microhabitat, behaviour, performance or any combination of these. During both embryo and larva periods of development, steps increased in time duration, indicating different rates of complexity of physiological and morphological developments within each step. From the results, a 'step like' model is proposed for the early development of sunbleak. (C) 2004 The Fisheries Society of the British Isles.