Morphological development of eggs, larvae and juveniles of laboratory-reared Ryukyu-ayu Plecoglossus altivelis ryukyuensis

ABSTRACT:   The development of embryos, larvae and juveniles of the Ryukyu-ayu, Plecoglossus altivelisryukyuensis are described based on laboratory-reared specimens.The eggs were spherical, 0.98–1.18 mm (mean 1.06 mm)in diameter with an adherent membrane. The incubation period after fertilizationwas approximately 155 h at a water temperature of 19.7–22.0°C(mean 20.7°C). Newly hatched larvae were 5.0–5.9 mm(mean 5.5 mm) in body length (BL) with 59–62 myotomes.Within 5 days after hatching, the larvae had attained 6.4–8.2 mm(mean 7.8 mm) BL and had completely consumed their yolk.Notochord flexion began at 13.7 mm BL and was completedby 16.3 mm BL. The rudimental dorsal, anal, pelvic andadipose fins appeared at 14.7, 16.3, 21.8 and 21.8 mm BL, respectively.All fin rays reached the same fixed number of adult fish at about28 mm BL. The comb-like teeth began to form at approximately30 mm BL and were fully developed at about 40–50 mm BL.The proportions of P. a. ryukyuensis specimens,which were consistent with adult fish, occurred at approximately40 mm BL.     

低排泄氮量的鹌鹑改良选育

选用日本鹌鹑N、B（Normal、Brown）品系和杂种群（BN）,共进行8个世代（6～20周龄）的选育试验,各品系采用单因子试验设计,在CP18％日粮条件下分选育组、非选育组以及对照组（CP24％）,N、B基础群中选留15种家系,以采食量为主选性状,以产蛋率和排泄氮量为辅选性状作为选育指标进行试验。结果表明：随着世代数的增加选育组和对照组的适应力均有显著升高（P〈0．05）,N品系的各世代遗传改进量为0．26;另外,世代间产蛋率有增高的倾向,选育组平均累积产蛋率与非选育组较显著升高（P〈0．05）,特别是选育组各世代遗传改良极为显著（P-〈0．01）。各世代间采食量无显著差异,同世代各品系间选育组N、B采食量均高于非选育组,但显著低于对照组（P〈0．05）。选育组排泄氮量和血清中尿酸含量在改良2世代后明显低于非选育组和对照组（P〈O．05）,排泄氮量分别降低7％～15％。综上所述,通过选育N、B新品系,能够改善产蛋性能,且显著降低排泄氮量,在BN杂种群中效果更明显。