International Journal of Marine Science, 2025, Vol.15, No.3, 167-178 http://www.aquapublisher.com/index.php/ijms 176 7.2 Multi-generation breeding program for Haliotis midae South African pearl abalone (Haliotis midae) is the most important aquaculture shellfish in South Africa, and has achieved large-scale aquaculture since the 1990s. In order to improve its production efficiency, South Africa has implemented a systematic genetic improvement plan since the beginning of the 21st century. The plan is promoted by scientific research institutions and breeding enterprises, including establishing breeding family lines, estimating genetic parameters, and selecting parents with excellent performance to breed the next generation. The specific method is to select several pairs of pro-agrants from the breeding population every year for single-pair mating, and establish dozens of family lines of all compatriots. After the family seedlings were independently cultivated to a certain size, the shell length and weight were measured, and survival and growth performance were evaluated under the same conditions. BLUP and other methods were used to estimate the breeding values of each family, and based on this, several best families and individuals were selected as parent groups for the next generation (Difford et al., 2017). Since 2002, the South African abalone breeding program has been continuously selected and bred for more than 5 generations. Breeding results show that the growth traits of abalone have made significant progress: the average shell length and weight of the 4th generation breeding population increased by about 20% compared with the basal population, and the growth cycle was shortened by 4-6 months. At the same time, the feed conversion efficiency has also been improved, and the feed consumption per unit of weight gain has been reduced by about 10%. In terms of survival rate, although there is a large natural variation, the overall survival rate has also increased after several generations by eliminating early high death families. Genetic parameters study shows that the heritability of the shell length, width and weight of South Africa's abalone shell is between 0.2 and 0.25, and the survival rate is only about 0.1. However, in high-density breeding environment, the survival rate is positively correlated with growth traits, that is, the survival rate of faster-growing families is often higher. This provides convenience for both survival in choice. Breeding programs in South Africa also pay special attention to the application of molecular markers. Since the 2010s, researchers have developed microsatellite and SNP markers of South African abalone and used for family paternity testing and genetic diversity monitoring. The results show that through reasonable selection and large group breeding, sufficient genetic variation in the population can be maintained while improving the traits. 7.3 Multiomics study on tropical hybrid abalone in Hainan, China One of China's innovations in abalone breeding is to cultivate tropical abalone varieties that are adapted to the high-temperature seas in the south. Traditional wrinkle plate abalone likes cold water and is not resistant to high temperatures, while tropical nine-hole abalone is small in individual and grows slowly. In order to take into account both large individuals and heat resistance, researchers carried out interspecies hybridization of abalone and created tropical hybrid abalone varieties. The most representative one is the "rebeaten No. 1" hybrid abalone (also known as "hybrid abalone I") cultivated by the Nanhai Institute of Oceanography, Chinese Academy of Sciences and other units. Its parent is a hybrid combination of female Ezo abalone × male variegated abalone. This hybrid abalone has the advantages of patriarchal heat resistance and maternal high yield. It can grow and reproduce normally in Hainan sea with high annual average water temperature, and is significantly improved compared with purebred wrinkled abalone. It is reported that the survival rate of "Reap Abalone No. 1" in the second half of the year under the water temperature of Hainan in summer was more than 90%, while the wrinkled abalone is less than 50%. In order to gain an in-depth understanding of the excellent trait mechanism of this hybrid abalone, researchers conducted a multiomic joint analysis of it. First of all at the genomic level, the genomic mutations of hybrid abalone and parents were compared using high-deep sequencing. It was found that most of the alleles of parents were preserved in the hybrid abalone genome and showed heterozygous advantages in the heat tolerance-related gene regions. For example, a hybrid abalone associated with HSP70 regulation simultaneously possesses different parental variants, which may confer stronger environmental resilience (Zhao et al., 2023). Next, in terms of the transcriptome, the differences in gene expression between hybrid abalone and purebred Ezo abalone under high temperature stress were compared. The results showed that the number of genes induced by hybrid abalone heat stress was greater, especially the gene expression level of the heat shock protein family was about 1.5 times that of purebred. This shows that hybrid abalone is more sensitive in molecular stress
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