饲料蛋白质水平对拉萨裸裂尻鱼幼鱼肌肉氨基酸及蛋白质代谢的影响

本实验旨在探索饲料蛋白质水平对拉萨裸裂尻鱼(Schizopygopsis younghusbandi Regan)幼鱼肌肉氨基酸及蛋白质代谢的影响。选用初始体重为(22.42±0.56) g 的拉萨裸裂尻鱼 540 尾,随机分成 6 组,每组 3 个重复,每个重复30 尾鱼,分别投喂蛋白质水平为 20%、25%、30%、35%、40%、45%的实验饲料,养殖时间为 60 d。结果表明:随着饲料蛋白水平的增加,拉萨裸裂尻鱼氮摄入量(NI)和绝对氮摄入量(ANI)均呈逐渐升高的变化趋势。氮沉积(ND)、蛋白质效率(PER)、净蛋白质利用率(NPU)均呈先升高后降低的变化趋势。肌肉总必需氨基酸(TEAA)、总呈味氨基酸(TFAA)、总非必须氨基酸(TNEAA)、总氨基酸(TAA)随饲料蛋白的升高呈先升高后趋于稳定的变化趋势。饲料蛋白水平超过 30%后,血氨(ammonia)、尿素氮(urea)、白蛋白(ALB)显著升高。总蛋白(TP)在饲料蛋白低于 35%时呈逐渐升高的变化趋势。拉萨裸裂尻鱼肝脏谷丙转氨酶 ALT、谷草转氨酶 AST 均呈先升高后趋于稳定的变化趋势,血清 ALT呈先降低后升高的变化趋势,血清 AST在饲料蛋白含量高于 35%后显著升高。综合考虑饲料蛋白利用率、血液总蛋白含量、肝脏及血清转氨酶活性,建议拉萨裸裂尻鱼饲料蛋白含量为 30%~35%。

Effects of dietary protein levels on muscular amino acids and protein metabolism of Schizopygopsis younghusbandi younghusbandi Regan

The goal of this experiment was to investigate the effects of dietary protein levels on muscular amino acids and protein metabolism of Schizopygopsis younghusbandi younghusbandi Regan. Six diets were formulated that contained 20%, 25%, 30%, 35%, 40%, and 45% protein levels. Each diet was fed to triplicate groups of 30 fish with an initial body weight of (22.42±0.56) g for 60 d. The results showed that both nitrogen intake (NI) and the amount of absolute nitrogen intake (ANI) of S. younghusbandi younghusbandi Regan increased with the increase in dietary protein levels. The nitrogen deposition (ND), protein efficiency ratio (PER), and net protein utilization (NPU) increased at first and then decreased. Total essential amino acids (TEAA), total flavored amino acids (TFAA), total non-essential amino acids (TNEAA), and total amino acids (TAA) initially increased and then tended to stabilize with the raising supplemental dietary protein level. There was no significant difference in blood ammonia, urea nitrogen, or albumin (ALB) at the feed protein levels of 20%-25%; however, these factors increased significantly after the feed protein level increased significantly after 30%. Total protein (TP) increased gradually when feed protein was lower than 35%, and there was no significant difference among the experimental groups when feed protein was higher than 35%. Both the liver ALT and AST increased at first and then tended to stabilize. There was a tendency for serum ALT to decrease first and then increase. Serum AST was not significantly different in the experimental group with feed protein content below 35% but increased significantly above 35%. Thus, the appropriate amount of dietary protein level can increase the absorption of protein, increase the protein utilization from feed, increase the rate of body protein metabolism, improve the content of essential amino acids, and improve the taste of muscle. However, it can cause a decrease in the protein utilization in the fish body, inadequate absorption of the protein in the intestine, the increase nitrogen excreta, aggravate the liver load, and damage liver cells when the content of feed protein is too high. Under these experimental conditions, the suitable dietary protein level was 30%-35% based on the feed protein utilization, total protein content in blood, and liver and serum transaminase activity.