凡纳滨对虾在低氧环境下存活性状的遗传参数评估

Evaluation of genetic parameters for survival traits of Litopenaeus vannamei under hypoxic conditions

中文关键词: 凡纳滨对虾  低溶解氧  遗传力  组织损伤  选育

英文关键词: Litopenaeus vannamei  Hypoxemia  Heritability  Tissue injury  Breeding

中文摘要:

      在水产养殖中，尤其是高密度养殖情况下，缺氧会短期内造成个体的大量死亡，从而影响生产效益。本研究以凡纳滨对虾(Litopenaeus vannamei)高抗和快大2个品系作为研究对象，利用高致死溶解氧(DO)胁迫的方式，对2个品系各41个家系共计6 560尾幼虾进行低氧耐受性测试，统计高致死溶解氧水平下幼虾的存活性状，分析不同品系间及同一品系不同家系间耐低氧性状的差异，评估其遗传参数；对耐受性有显著差异的家系个体的鳃、肌肉、肝胰腺组织进行组织学观察，并比较其细胞水平上的差异。结果显示，在0.3 mg/L低氧条件下，高抗品系和快大品系的家系半致死存活率SS50均表现出显著差异(P<0.05)，高抗品系SS50为49.30%，快大品系SS50为42.52%；家系间存活时间的变异系数分别为60%和45%。利用阈值性状动物模型，以半致死时的个体存活状态作为观测值(存活为1，死亡为0)估算的遗传参数为(0.345±0.031)~(0.378±0.029)，经过转换后在连续变化的观测值尺度上的遗传力为(0.219±0.031)~(0.237±0.029)，表现为中等遗传力水平。高抗品系中低氧耐受家系和低氧敏感家系的鳃、肌肉和肝胰腺组织均出现不同程度的损伤，但不同的家系间表现出不同程度的抗逆生理特征差异，这可能与高抗不同家系抗逆耐受力强弱有关。不同家系间在低氧胁迫下的存活时间、生理特性差异以及各品系遗传力估算结果表明，凡纳滨对虾对高致死溶解氧水平的耐受性状存在丰富的遗传变异，具有选育的可行性。

英文摘要:

      Litopenaeus vannamei, also known as the Pacific white shrimp or white foot shrimp, is a member of the Crustacea, Decapoda, Palaemonidae, and Litopenaeus families. This species is mainly distributed on the Mexican and Pacific coasts of South America. Owing to its excellent immune characteristics, L. vannamei is currently one of the most important economic shrimp species in China. In the aquaculture process and under natural environmental conditions, low dissolved oxygen (DO) condition or even hypoxia frequently occurs. Under high-density culture operations, acute hypoxia is one of the major factors affecting the survival rate of shrimp and the quality of aquaculture water, causing not only a large number of shrimp deaths in the short term but also water decay and fermentation, increased turbidity, and other phenomena. The genetic improvement of L. vannamei, as well as the screening and breeding of exceptionally tolerant species under low DO conditions, are crucial to the sustainable development of the shrimp industry. Global selective breeding efforts based on quantitative genetics to improve genetic progress in L. vannamei have been extensive, and the main targeted traits were growth, survival, disease resistance, and stress tolerance. Few studies have been conducted on the evaluation of genetic parameters and screening of strains for hypoxic tolerance traits in L. vannamei; in particular, the genetic parameters and cytological characteristics of key tissues of L. vannamei under short-term highly lethal DO levels (0.3–0.5 mg/L) have not been reported. In this study, we used two strains of L. vannamei, GK (a strain with high disease resistance) and K (a strain with fast growth characteristics), each with a total of 6 560 shrimp from 41 families, to count survival traits at highly lethal DO levels, analyze differences in hypoxia tolerance traits between strains and within families of the same strain, and evaluate genetic parameters. Individual gill, muscle, and hepatopancreas tissues from families with significantly different tolerance levels were histologically investigated and compared at the cellular level. The results showed that there was a significant difference (P<0.05) in semi-lethal survival (SS50) between families within both the GK and K strains when overall semi-lethality was reached under hypoxic environmental conditions of 0.3 mg/L, with SS50 values of 49.30% for GK and 42.52% for K. The coefficients of variation for survival times of families within each strain were 60% and 45% for GK and K, respectively. Using the threshold trait animal model, the genetic parameters were estimated to be between 0.345±0.031 and 0.378±0.029 using the survival status of the individual at semi-lethal levels as the observed value (1 for survival and 0 for death), and the heritability was between 0.219±0.031 and 0.237±0.029 following transformation on a continuously varying scale of observed values, indicating a moderate level of heritability. Moreover, the gill, muscle, and hepatopancreas tissues of the hypoxia-tolerant and hypoxia-sensitive families in the GK strain exhibited varying degrees of damage and different degrees of variations in the physiological characteristics of resistance among different families. This may be related to the resistance tolerance strength of different GK families. In contrast to the gill, muscle, and hepatopancreas tissues of the control shrimp, the equivalent tissues of shrimp from tolerant and sensitive families showed different degrees of changes following stress. The gill lumen of the filaments of the experimental group from sensitive families increased, the number of blood cells increased, the structure of the epithelial layer was gradually destroyed or even disintegrated, the vacuolation of the hepatopancreas was severe, the lumen of the ducts became irregularly deformed, and the muscle tissue muscle bundle interval widened with a certain degree of deformation. These results suggested that there was abundant genetic variation in the tolerance traits of L. vannamei at highly lethal DO levels and that this species was amendable to selective breeding practices. This study provides a reference and basis for the selection and breeding of hypoxia-tolerant traits in L. vannamei.