盐度对凡纳滨对虾体组织蛋白质积累、氨基酸组成和转氨酶活性的影响

本文研究了低、中和高三个盐度水平(分别为3‰、17‰和32‰)对凡纳滨对虾(Litopenaeus vannamei)各组织蛋白质的积累、肌肉谷草转氨酶和谷丙转氨酶活力、肌肉总氨基酸和游离氨基酸组成和含量的影响。结果显示，经过50d不同盐度水平的试验，低盐度组对虾的肝胰腺和血淋巴中可溶性蛋白质含量显著高于中、高盐度组(p<0.05)，而肌肉中可溶性蛋白质含量在各处理组间无显著性差异；低、高盐度均导致肌肉中谷丙转氨酶和谷草转氨酶活力升高，但是各处理间的差异不显著；低、高盐度组凡纳滨对虾肌肉总氨基酸和总必需氨基酸含量均显著高于中盐度组(p<0.05)，中、低盐度处理组非必需氨基酸含量差异不显著，而低盐度组对虾肌肉中蛋氨酸、丝氨酸、半胱氨酸和脯氨酸含量均显著低于中盐度组(p<0.05)，其中脯氨酸为常见的5种主要渗透调节氨基酸之一；低、高盐度组对虾肌肉总游离氨基酸含量显著高于中盐度组(p<0.05)，而盐度对机体绝大部分肌肉游离氨基酸含量的影响不显著(p>0.05)。结果显示，当环境盐度偏离凡纳滨对虾最适生长盐度时，其可通过在肝胰腺和血淋巴蛋白质积累及提高自身转氨酶活力，来获得机体在渗透调节供能时所需的氨基酸，而这些氨基酸以脯氨酸为主。

PROTEIN ACCUMULATION ,AMINO ACID PROFILE AND AMINO TRANSFERASE ACTIVITIES OF THE WHITE SHRIMP, LITOPENEA US VANNAMEI, AT DIFFERENT SALINITIES

Shrimp farming in inland saline water has been undertaken in many parts of the world. Particularly, the culture of white shrimp, Litopenaeus vannamei, has becoming a rapid growing industry due to its tolerance to a wide range of salin-ity from 1‰ to 50‰. Although L. vannamei are euryhaline and able to tolerance a wide range of salinity, a salinity change does alter its growth performance and physiological responses. And even the optimal salinity for the growth of white shrimps is controversial, research on L. vannamei at low salinity is still limited. The physiological responses are believed to be es-sential to assess the animal performance at different environmental conditions. Therefore, it is necessary to conduct further investigation on the physiology of L. vannamei at low salinity for inland saline water farming.The objective of this study was to further explore the adaptive mechanisms of white shrimp to different salinities in providing extra energy for osmoregulation at various salinities, and to explore which amino acids are the main osmolytes for L. vannamei. Therefore, shrimps which have been acclimated at 3.0%, 17.0‰ and 32.0‰respectively with four repli-cates for 50 days were used to analyze the soluble protein of different tissues, muscle amino acid profile and contents, Glatamic oxalaeetic transferase (GOT) and Glutamat Pyruvat Transferase (GPT) activities. During the experimental peri-od, the shrimp were fed with a commercial feed containing 40.02% protein, 8.5% crude lipid, 12.0% ash, and 10.2% moisture, and Reeirculation systems were used in the experiment. The results showed that shrimps at 3.0‰ had signifi-cantly higher soluble protein content of hepatopancreases and heamolymph than those at both 17.0‰ and 32.0‰ (p < 0.05 ), while no significant differences were observed in the tissue of muscle (p >0.05 ). Low salinity 3.0‰ and high salin-ity 32%0 led to the slight increase of both GOT and GPT activities in muscle though without significant differences (p >0.05 ) comparing with 17.0‰ treatment. Shrimps at 3.0‰ and 32.0‰ had significant higher levels of total amino acids and total essential amino acids in muscle than those at 17.0‰ (p < 0.05 ), and non essential amino acids in shrimps at 3.0‰ and 17.0‰ showed no obvious differences. However, the total muscle methionine, serine, cysteine and proline contents of shrimps at 3.0‰ were significantly lower than those at 17.0‰ (p < 0.05), and among which the praline is one of the main five osmolyte amino acids for aquatic animals. Most muscle free amino acids were not different significantly among all the treatments (p > 0.05 ).All these results indicated that under salinities away from its optimal salinity, the white shrimp ensured themselves to have sufficient amino acids for osmoregulation by accumulating protein in the hepatopancreas and heamolymphs, and accel- erating the amino transfer speed by increasing Glatamic oxalaeetic transferase and Glutamat Pyruvat Transferase activities. Besides, the results also revealed that as one the main five osmolyte amino acids, the amino acid of proline is the main one among these amino acids which play important roles for osmoregulation for L. vannamei.