Estimation of Genetic Parameters for Growth and Acute Hepatopancreatic Necrosis Resistance in Different Strains of Penaeus vannamei

The Pacific white shrimp or white leg shrimp, Penaeus vannamei, is native to the tropical coastal regions of Central and South America. It is one of the three major shrimp species with high production worldwide. It was brought from Hawaii, USA, in 1988 and introduced into China. It has been widely promoted and cultivated due to its adaptability to the environment, fast growth rate, and suitability for high-density industrial farming. As of 2022, China's total production of P. vannamei reached 2.09 million tons, accounting for > 90% of the country's total shrimp farming production. It has become one of the pillar industries in China's aquaculture sector.With the continuous expansion of aquaculture, diseases are becoming increasingly severe. Among them, acute hepatopancreatic necrosis disease (AHPND) hinders the development of the global shrimp farming industry and causes catastrophic economic losses. After infection, most shrimp show hepatopancreatic enlargement, which appears pale white or light yellow. In the later stages of infection, some diseased shrimp may exhibit atrophy of the hepatopancreas, appearing reddish-brown and blackened, with a hardened texture. Within 20–30 d after infection, death can occur, with a mortality rate of up to 90%. As of 2021, the economic losses caused by this disease to the major P. vannamei farming areas (China, Malaysia, Thailand, Vietnam, and Mexico) have exceeded 43 billion US dollars. Cultivating novel P. vannamei germplasm with AHPND resistance is an effective way to solve AHPND.Recently, domestic researchers have established independent shrimp breeding systems and cultivated 12 novel P. vannamei strains, such as "Hai Xing Nong No.2", "Ren Hai No.1", and "Zheng Jin Yang No.1". These varieties mainly target traits such as growth, resistance to white spot syndrome virus, farming survival rate, and temperature, salinity, and ammonia nitrogen tolerance. However, no reports of novel varieties specifically targeting AHPND resistance are available. Growth traits are essential economic traits in the genetic breeding of aquatic animals. Among the 12 novel P. vannamei varieties in China, 11 have excellent traits related to growth. Evaluating the genetic relationship between growth and AHPND resistance in the core breeding population of P. vannamei is important for fully utilizing existing high-quality germplasm and breeding novel varieties with composite traits and AHPND resistance.Genetic parameters reflect the genetic variation of target traits in a breeding population and are important references for breeding decisions. Due to the complex genetic background of existing P. vannamei germplasm resources in China, genetic parameters are influenced considerably by the tested population, infection methods, and other factors. Before breeding, stable infection tests must be conducted on the base population and obtain accurate parameters.This study used two independently bred P. vannamei strains as research objects to test their growth and AHPND resistance. Among them, 40 families were selected for high resistance (20 individuals per family, total 800 experimental individuals), and 30 families were selected for fast growth (32 individuals per family, total 960 experimental individuals). The test was conducted at P70–P90 by feeding with VpAHPND quantitative oral infection. Feeding with toxic bait was stopped after 50% of the experimental individuals died. The genetic heritability and correlation of the weight, individual survival time after VpAHPND infection, and half-lethal survival rate of the two strains were evaluated using individual animal and male and female threshold models. The results showed that the weight heritability estimate of the highly resistant strain was 0.599±0.120, indicating a high level of genetic heritability. The heritability estimates of survival time and half-lethal survival rate were 0.240±0.072 and 0.173±0.051, respectively, indicating a moderate to low level of genetic heritability, and all significantly different from 0 (P < 0.01). The weight heritability estimate of the fast-growth strain was 0.266±0.082, indicating a low level of genetic heritability. The heritability estimates of survival time and half-lethal survival rate were 0.374± 0.096 and 0.257±0.048, respectively, indicating a moderate level of genetic heritability, and all significantly different from 0 (P < 0.01). The genetic correlation between weight and AHPND resistance traits (survival time and half-lethal survival rate) in both strains showed a low positive correlation (0.061–0.235), and no significant difference was observed from 0 (P > 0.05). The genetic correlation between survival time and half-lethal survival rate in both strains was highly positively correlated, with estimates of 0.997±0.129 and 0.967±0.044, respectively. The results indicate that growth and AHPND resistance can be included as selection indicators in the comprehensive selection index for breeding and seed production in the actual breeding process. Under limited conditions, the infection program can be simplified, and the half-lethal survival rate can be used as the AHPND resistance indicator for the breeding population. This study provides a primary reference for utilizing existing germplasm resources to develop high-quality P. vannamei strains for growth and AHPND resistance breeding.