| This study examined the embryonic development, effect of water temperature on embryonic development, post-embryonic development, effect of water temperature and salinity on survival and growth of larvae of Navodon Septentrionalis (Günther), aimed at providing theoretical basis and practice direction for artificial breeding of Navodon Septentrionalis.Experiment 1: Study on Embryonic Evelopment of Navodon SeptentrionalisThe artificial reproduction technique of Navodon Septentrionalis was studied in summer, 2010, at Yantai Taihua Rare Sea Products Co. Ltd, Shandong Province, China. The gonad was promoted mature by controlling the water temperature and light condition in the culture apart stage of 2a～4a adult fish. Zygote was obtained by artificial insemination with collected mature eggs and sperms. The embryonic development was observed by microscope, the total development time of every development stage was noted and calculated and the characteristic images were taken using a digital camera (NIKON E4200). The fertilized eggs are globular, stickiness, thick egg membrane and the egg diameter is 0.59～0.66mm. Along with embryonic development, the all oil balls(there were 14～59 oil balls per egg at the early stage) consolidated to only one. Embryos were incubated in sea water (salinity 30～31)at 19.5±0.5℃. The time-table of major embryonic development stages was as follows: blastodisc forming stage at 0h20m post fertilization(pf); 4-cell stage at 0h50m pf; morula at 5h pf; low blastula stage at 10h12m pf; early gastrula stage at 12h pf; late gastrula at 18h33m pf; blastopore closing stage at 20h30m pf; 6-somite stage at 21h50m pf; tail bud stage at 34h10m pf; embryo movement at 40h40m pf; 50% hatching stage at 66h pf.Experiment 2: Effect of Water Temperature on Embryonic Development of Navodon SeptentrionalisThe embryonic development of Navodon Septentrionalis was observed at water temperature of 16, 18, 20, 22, 24, 26, 28, 30 and 32℃to evaluate the biological zero and effective accumulative temperature for the embryonie development.The embryos were found to develop normally at water temperature between 16～28℃and the incubation period was shorter when the water temperature increased. The newly hatched larvae died in one day with the water temperature was upper than 24℃. It was found that 20℃was the optimal water temperature for the embryonic development of Navodon Septentrionalis. The biological zero was found to be 6.84℃and effective accumulative temperature was calculated to be 798.45℃·h for the embryonic development of Navodon Septentrionalis.Experiment 3: Post-embryonic Development of Navodon SeptentrionalisMorphology of Navodon Septentrionalis in early life stage was studied, including features of yolk sac larva, pre-flexion larva, post-flexion larva and juveniles. Larvae were cultured in indoor concrete tanks with sand filtered natural seawater (salinity 30~31), and the cultivation conditions were: temperature 22～25℃, salinity 30-31, light strength 1000～2000lx with constant aeration. The newly hatched larvae rely on yolk nutrition untill 3dph (0～2dph, yolk-sac larvae). Mouth opened at 3dph (3～18dph, pre-flexion larvae).The tail end of notochord upwarped at 19dph (19～24dph, flexion larvae), the tail fin developed perfectly at 25dph (25～39dph, post flexion larvae). All fin rays and scales were formed at 40dph, the fish turned into juvenile stage, which having the same appearance as adults. The morphological development and changes of pigment pattern were observed.Experiment 4: Effects of Temperature and Salinity on Survival and Growth of Larvae Navodon SeptentrionalisThe survival and growth of larvae Navodon Septentrionalis (Günther) ware studied under different temperatures and salinities. The results showed that the larvae could grow and survive at temperature range 21～30℃, and most of the larvae died when the temperature was above 32℃; the optimum temperature range for the larvae was 21～24℃, and the growth rate would be slowed down when temperature was above 24℃. The larvae could grow and survive at salinity range 10～45, and most of the larvae died when the salinity was beyond the range; the optimum salinity range for the larvae was 25～35, and the growth rate would be slowed down obviously when the salinity was beyond the range. |
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