鲈幼鱼对饲料中苏氨酸的需要量

以初始体质量(8.00±0.20)g的鲈为实验对象,在海水网箱(1.5 m×1.5 m×2.0 m)中进行为期8周的摄食生长实验,研究鲈对饲料中苏氨酸的需要量。通过在半精制基础饲料中添加晶体L-苏氨酸使饲料中苏氨酸含量分别达到0.75%、1.03%、1.36%、1.67%、2.04%和2.31%,配制成6水平等氮等能饲料(41.83%粗蛋白质,19.68 kJ/g总能)。每种饲料设3个重复,每个重复随机放养30尾鲈。实验采用表观饱食投喂方式,每天投喂2次(06:00和17:30),实验期间水温为26～32℃,盐度为22～28,溶解氧含量在7 mg/L左右。实验结果表明,各饲料处理组成活率(94.4%～98.9%)无显著差异。随着饲料中苏氨酸含量的增加,鲈的增重率显著升高(150.3%～256.9%)(P<0.05),且在1.67%苏氨酸饲料组达到最大值(256.9%),然而,随着饲料中苏氨酸含量的进一步增加,增重率有下降的趋势。鲈的氮累积率随着饲料中苏氨酸含量的增加而显著升高(13.18%～26.36%)(P<0.05),且在1.67%苏氨酸饲料组达到最大值(26.36%),随着饲料中苏氨酸含量的进一步增加,氮累积率有下降的趋势。饲料苏氨酸含量对鲈鱼体粗蛋白、粗脂肪和灰分含量无显著影响。以增重率和氮累积率为评价指标经二次回归分析得出,鲈对饲料中苏氨酸的需要量分别为1.77%和1.88%,占饲料蛋白质的4.21%和4.47%。

Dietary threonine requirement of juvenile Japanese seabass(Lateolabrax japonicus)

A feeding experiment was conducted to determine the dietary requirement of threonine of juvenile Japanese seabass(initial average weight 8.00±0.20 g).Six isonitrogenous and isoenergetic semi-purified diets were formulated to contain 41.83% crude protein,19.68% kJ/g gross energy and six levels of threonine 0.75%,1.03%,1.36%,1.67%,2.04% and 2.31%(dry matter basis)at about 0.35% increment(diets 1-6).Each diet was randomly assigned to triplicate groups of 30 fish and fed to apparent satiation by hand twice daily(06:00 and 17:30)for 8 weeks in floating sea cages.The water temperature fluctuated from 26 to 32 ℃,salinity from 22‰ to 28‰ and dissolved oxygen was approximately 7 mg/L during the experimental period.No significant differences in survival were found among dietary treatments.Weight gain rate(WGR)significantly increased with increasing dietary threonine from 150.3 to 256.9%(P<0.05),and thereafter showed a declining tendency.Nitrogen retention(NR)significantly increased with increasing dietary threonine from 13.18% to 26.36%(P<0.05),same as above,declined.No significant differences in body composition were found among dietary treatment.On the basis of either WGR or NR,the optimum dietary threonine requirements of juvenile Japanese seabass were estimated to be 1.77% of diet(4.21% of dietary protein)and 1.88% of diet(4.47% of dietary protein),respectively,using second-order polynomial regression analysis.