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The northern pike is one of the important economic fish in Xinjiang, China. However, its survival and the expansion of aquaculture areas have been seriously affected by the increase in water temperature caused by global warming and the extremely high temperature in summer. Therefore, screening molecular markers and candidate genes will be helpful for the selection of heat tolerance of the northern pike, which will be beneficial to its better survival and expansion. In this study, the heat tolerance and cumulative survival time of the northern pike were measured under high temperature stress (26 °C ~ 35 °C). Genome-wide association study (GWAS) was used to analyze the loci and genes related to heat tolerance of the northern pike. A total of 77,617 single nucleotide polymorphisms (SNPs) were obtained through genotyping by sequencing (GBS) and used for subsequent GWAS analysis. 9 significant SNPs were obtained from GWAS analysis, which were assigned to eight chromosomes. By analyzing these significant SNPs, we predicted four candidate genes (clstn2 , htr4 , atp13a3 and schip1) related to respiration, ion channels, or obesity. The heat tolerance of the northern pike was determined by a variety of mechanisms regulated by various genes. The results observed in this study provide insights into the genetic basis of heat tolerance in the northern pike and contribute to the cultivation of heat-resistant fry. • This is the first time to conduct GWAS analysis on the heat tolerance of the northern pike. • A total of 77,617 SNPs were obtained through GBS for subsequent GWAS analysis. • Nine significant SNPs and four candidate genes related to long-term survival under high temperature stress were identified. [ABSTRACT FROM AUTHOR]

Grass carp (Ctenopharyngodon idella) is a highly productive freshwater fish species that is widely cultivated worldwide, contributing substantial economic value to the aquaculture industry annually. Recently, a breeding program for grass carp has progressed to the fourth generation (F 4) after four consecutive generations of family selection. To further assess the growth performance of the genetically selected grass carp F 4 , a 90-day consecutive growth comparison experiment was conducted between the selected population and a wild base population. The results showed that the selected grass carp F 4 had better growth performance. Whole-genome resequencing of both wild and selected populations of grass carp yielded a total of 4,354,416 high-quality single nucleotide polymorphisms (SNPs). Parameters of genetic diversity including observed heterozygosity (H o), expected heterozygosity (H e), nucleotide diversity (π), and polymorphic information content (PIC) were slightly decreased in the selected population compared to the wild population. The fixation index (F st) indicated a low level of genetic differentiation (F st = 0.021). Selection signatures analysis identified a total of 173 candidate selected regions with a cumulative size of 23.75 Mb, and 912 candidate genes including igf-1r , igfbp-2 , igfbp-5 and itga6. This study provides valuable insights into the growth performance and the genetic basis of selection signatures in the process of grass carp selective breeding, and offers guidance for future breeding programs. • Growth performance of the genetically selected grass carp F 4 was assessed. • High-density SNPs of grass carp were identified using whole-genome resequencing technology. • Parameters of genetic diversity were slightly decreased in the selected population compared to the wild population. • Selected regions and candidate genes were detected after four consecutive generations of grass carp breeding program. [ABSTRACT FROM AUTHOR]