Evaluation of Genetic Parameters for Growth and Survival Traits of Penaeus vannamei During White Spot Syndrome Virus Infection

Abstract

Penaeus vannamei, also known as white foot shrimp, is globally one of the three high-yield shrimp farming varieties. The wild species is found along the Pacific coast of South America. Since 1988, China has introduced P. vannamei. Due to its strong environmental adaptability, high feed conversion rate, fast growth rate, and high tolerance to ammonia nitrogen and nitrite, it has been widely promoted in aquaculture. By 2021, the aquaculture output of P. vannamei in China reached 1.977 million tons, accounting for approximately 37% of the world's total production, and has extremely high economic value.Growth traits are among the most important economic factors in the production of P. vannamei. With the intensive development of shrimp farming and degradation of germplasm, the white spot syndrome virus (WSSV) is a serious disease faced by the global shrimp industry. The infection can cause symptoms such as reduced food intake, enlarged liver and pancreas, pale red body color, and white spots on the head and chest armor in shrimp, resulting in widespread death.At present, China has cultivated 12 new varieties of P. vannamei, which to some extent alleviates its dependence on imports for high-quality P. vannamei. However, the excellent traits of domestic shrimp species are singular, and cultivating new varieties of P. vannamei with fast growth and strong disease resistance is an urgent demand in the market. Genetic parameter evaluation is the fundamental work of selection breeding. Heritability reflects the genetic variation in traits in the breeding population, which is of great significance in the development of a selection index, prediction of selection response, comparison of selection methods, selection breeding planning, and other breeding processes. There are different degrees of genetic correlation among various quantitative traits of shrimp, and genetic correlation coefficients are important for selecting target traits. The estimation of genetic correlation can be used to develop a comprehensive selection index and breeding program of multiple traits, which can improve the selection efficiency and breed better varieties with multiple traits. The higher the genetic correlation between traits, the better the effect of indirect selection. The estimation of genetic parameters is greatly affected by the test population, breeding management, analysis methods, and other factors. To ensure the accuracy of multi-trait composite breeding for growth and WSSV resistance, accurate evaluation of growth and WSSV resistance needs to be carried out for specific breeding populations. There are two commonly used target traits for measuring WSSV resistance in P. vannamei: individual survival time after infection and half-lethal survival rate (SS50) of families. In practice, measuring the half-lethal survival rate of families is more convenient. However, the correlation between these two traits has not yet been reported.To promote the growth and WSSV resistance of P. vannamei, 59 families (1, 770 individuals) were tested for WSSV infection. We recorded the survival time and individual body length of shrimp after infection and analyzed the mean, standard deviation, maximum and minimum values, and coefficient of variation of half-lethal survival rate and test traits for each line. The heritability and genetic correlation coefficients of growth, survival time, and half-lethal survival rate were calculated. Variance components and genetic parameters for growth and survival traits were estimated using a two-trait animal model and a sire-dam threshold model. The genetic parameters of body length were corrected by including age as a covariate. The genetic parameters of WSSV survival time were corrected by including body length as a covariate. The estimated heritability of body length was medium (0.17±0.05), and the estimated heritabilities of survival time and half-lethal survival rate were medium (0.18±0.05 and 0.14±0.05). Further, the estimated heritabilities of the three traits were significantly different from zero (P 0.05). The genetic correlation between survival time and half-lethal survival rate was high (0.96±0.03). There was no significant difference between the genetic correlation and one (P > 0.05). The results showed that a comprehensive selection index of growth and WSSV resistance of P. vannamei can be established to carry out multi-trait composite breeding. In this breeding population, the growth and WSSV resistance of P. vannamei can be combined with multiple traits according to the breeding requirements, and the comprehensive selection index can be formulated by assigning values. In addition, to optimize the breeding of each generation, the half-lethal survival rate of WSSV can be used as an indicator of WSSV resistance. This study provides basic data and theoretical support for breeding varieties of P. vannamei with excellent growth and WSSV resistance.

Keywords

• penaeus vannamei
• genetic parameters
• growth
• survival
• white spot syndrome virus