Early ontogenesis of Brachymystax lenok tsinlingensis

Sexually mature Brachymystax lenok tsinlingensis were caught from the wild and,after artificial fertili-zation,embryonic and larval development were investigated.Larvae of mean body length(9.64 ± 1.03) mm hatched 408 h after fertilization.The total accumulated temperature of embryonic development was 193.35℃·d at a water temperature of 9.31-12.80 ℃.We defined six broad stages of embryogenesis(zygote,cleavage stage,blastula stage,gastrula stage,neurula stage,and organ formation stage),which included 26 minor periods.The hatching larvae had a transparent body with clearly visible sarcomeres,but with limited swimming capability.Five days after hatching,a patch of melanin appeared on the body surface.The yolk sac began to disappear 12 days after hatching and parr markings started to appear after 46 days,at which stage the fins of the larvae resembled those of young fish.The morphological characteristics of the embryos and larvae are described and the factors affecting ontogenesis of the early life stages of Brachymystax lenok tsinlingensis,including water temperature,dissolved oxygen and water quality,are discussed.