Embryonic and Early Larval Development of Schizothorax wangchiachii

Schizothorax wangchiachii is one of the primary economic fish in the Jinsha River and its tributaries. The species is also ecologically important and one of the indigenous fish listed in the artificial breeding and release program for Longkaikou and Ahai hydropower stations on the middle Jinsha River. The potential for large-scale culturing of S. wangchiachii is indicated by high market demand and declining wild populations. However,little is presently known about embryonic and larval development of S. wangchiachii. In this study embryonic and early larval stage S. wangchiachii,maintained under controlled laboratory conditions,were described and illustrated. On March9,2014,parental stock was selected from the breeding and release station at Longkaikou hydropower station and a total of 67 860 zygotes were obtained by dry fertilization. The incubation of zygotes and the culture of yolk-sac larvae were conducted in an incubator at constant water temperature( 14 ± 1) ℃ and embryonic and larval development were observed using a Nikon stereoscopic anatomical lens and recorded with a Nikon DS-Fil high-definition camera. At least 30 zygotes were sampled once each hour during the first 48-hour zygote development phase and then sampled once every two hours after that. Twenty larvae were sampled each day. Results show that mature and fertilized eggs were demersal,weakly glutinous with abundant yolk. The average diameter of fertilized eggs was2. 36 mm and 3. 68 mm after swelling. Cleavage began at 6 h 30 min after fertilization at( 14 ± 1) ℃. Blastula,gastrula and mid-gastrula stages occurred,respectively,at 20 h 55 min,60 h 28 min and 70 h 4 min after fertilization. The neurula stage occurred at 77 h 52 min and muscles were observed to shrink at 142 h after fertilization.Heart pulsation began at 177 h 46 min and the newly hatched larvae were released from the membrane at 254 h40 min after fertilization. Cumulative temperature was up to 3 565. 3℃ ·h during the development process. The average total length of newly hatched larvae was 8. 7 mm. The pectoral fins,gills,mouth cavity,eye pigmentation,blood vessels and other organs developed gradually from day 2-9 after hatching. On day 10 after hatching,the larvae reached 15. 15 mm and initial swim bladder inflation began. Yolk-sac absorption was complete after day 10 and the larvae could swim horizontally and began to search for food( rotifers were supplied). The development time sequence and morphological characteristics of Schizothorax wangchiachii development from zygote to yolk-sac larvae presented here will lay a theoretical foundation for industrial breeding of S. wangchiachii.