低盐度条件下的凡纳滨对虾幼虾亮氨酸营养需求

为了探讨低盐度(0.6～0.8 g/L)条件下初始体质量为(0.38±0.004)g的凡纳滨对虾(Litopenaeus vannamei)幼虾的亮氨酸需求量,以鱼粉、花生麸和L-晶体氨基酸为蛋白源配制含粗蛋白400 g/kg的6种等氮饲料,标记为L7～L12组,各组亮氨酸水平分别为15.95、17.95、19.95、21.95、23.95和25.95 g/kg(饲料干物质).每组3个重复,每个重复30尾虾,进行56 d生长实验.结果表明,凡纳滨对虾幼虾的增重率随饲料亮氨酸水平的升高而升高,当亮氨酸水平达到23.95 g/kg(L11组)时,增重率达到最高值(1143.11±36.40)％,显著高于L7组(P＜0.05);亮氨酸水平继续提高,增重率变化不显著(P＞0.05).幼虾的蛋白质效率、全虾体蛋白沉积率和血淋巴总蛋白随着饲料亮氨酸水平的升高呈现升高趋势,最高值出现在L11组,并显著高于L7组(P＜0.05).各实验组饵料系数、血淋巴谷丙转氨酶、谷草转氨酶活性和尿素氮含量则呈现降低的趋势,最低值出现在L11组,且显著低于L7组(P＜0.05).以增重率为指标,根据折线模型可知,低盐度条件下凡纳滨对虾幼虾的亮氨酸最适需要量为24.80 g/kg饲料,即61.99 g/kg饲料蛋白.

Quantitative dietary leucine requirement of juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) reared in low-salinity water

  The Pacific white shrimp, Litopenaeus vannamei, originated in Pacific coastal waters but are now widely farmed in inland China and are one of the most important farmed aquatic species world-wide. Leucine plays an important role in the maintenance of nitrogen balance, energy metabolism, blood glucose concentration, growth hormone and hemoglobin concentration, and also stimulates protein synthesis in muscle tissues. Thus, a deficiency of leucine in diets can cause severe biochemical malfunction, including growth retardation. Until now however, the optimal leucine requirements of white shrimp were unknown. We evaluated the leucine requirements of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low-salinity water(0.60.8 g/L). Six diets containing fish meal, peanut meal and crystalline amino acids with different concentrations of L-leucine(15.95, 17.95, 19.95, 21.95, 23.95, and 25.95 g/kg dry diet) were formulated to contain 400 g/kg crude protein. A total of 1 000 healthy shrimps (initial body weight:  0.38±0.004 g) were randomly distributed into 18 rectangular fiberglass aquariums (280 L, 3 aquaria per diet, 30 shrimps per aquarium) and fed one of the diets for 56 d. Weight gain rate increased significantly with increasing leucine concentration up to 23.95 g/kg dietary leucine (diet L11, P<0.05). The diets containing higher leucine concentrations had no effect on growth performance (P>0.05). Group L11 had the highest protein efficiency ratio (PER), body protein deposition (BPD), hemolymph total protein (TP), and the lowest feed conversion ratio (FCR), hemolymph aspartate aminotransferase (AST), alanine transaminase (ALT) activities, and hemolymph urea nitrogen (HUN) content. The PER, BPD, and TP of group L11 were significantly higher than those of group L7, whereas the FCR, AST, ALT, and HUN of group L11 were significantly lower than those of group L7(P<0.05). The survival of group L7 was lower than that of group L9 and L10 (P<0.05), but there was no significant difference among the other groups(P>0.05). Our results suggest that a lack of dietary leucine decreases growth performance and survival of Pacific white shrimp. A broken-line regression calculated using weight gain rate indicated that the optimal dietary leucine requirement for L. vannamei reared in low-salinity water was 24.80 g/kg leucine of dry diet, corresponding to 61.99 g/kg  leucine of dietary protein.