Bioscience Methods 2025, Vol.16, No.3, 162-172 http://bioscipublisher.com/index.php/bm 165 Adaptive immunity has also evolved in fish, but it has some unique features compared to mammals. Teleost fish have T lymphocytes and B lymphocytes, as well as corresponding immunoglobulins (Ig). Snakehead fish's B cells can secrete two types of antibodies, IgM and IgT. IgM mainly circulates in the blood, while IgT is a mucosal antibody unique to fish, concentrated in mucosal tissues such as the intestines and gills, and plays an important role in mucosal immunity (Liu et al., 2025). Snakehead fish's immune system can resist pathogens through the rapid response of innate immunity and the specific memory of adaptive immunity. A key factor affecting snakehead fish's disease resistance lies in the diversity and regulatory efficiency of its immune genes. There are significant differences in the intensity of immune responses among individuals with different genotypes (Fraslin et al., 2020; Liu et al., 2025) 2.3 Current status and existing problems of disease resistance gene research In recent years, a series of progress has been made in the study of genes related to immunity and disease resistance in snakehead fish, but overall it is still in the stage of discovery and functional identification, with problems such as insufficient functional verification and unclear gene networks. In terms of candidate gene screening, researchers have mainly adopted two strategies: one is genome-level scanning, such as constructing a high-density genetic linkage map and locating QTLs for disease resistance traits, but there are few reports on the study of disease resistance QTLs in snakehead fish; the second is transcriptome or proteomics comparison, screening differentially expressed genes before and after infection. The latter has been applied in snakehead fish and its hybrids (Chen et al., 2018). For example, Zhang et al. (2022) used RNA sequencing to compare the spleen transcriptomes of healthy and nocardia-infected hybrid snakehead fish, and identified more than 3,500 differentially expressed genes, many of which are involved in innate immunity and inflammatory pathways. In terms of the identification of core disease resistance genes, several specific genes have been reported to be closely related to snakehead fish immunity or disease resistance. Han et al. (2025a) identified all 7 members of the snakehead fish IL-17 cytokine family and their receptor genes, a total of 9 members, and found that snakehead fish IL-17 is highly conserved in evolution. When stimulated by Nocardia, especially IL-17C2, IL-17D, IL-17N and other subtypes are significantly upregulated in the gills and intestines of fish, suggesting that they play a key role in mucosal immune defense. In terms of functional verification and mechanism of action, the current research on snakehead fish disease resistance genes is not deep enough, mostly staying at the level of identification and expression analysis, lacking direct functional evidence. On the one hand, because snakehead fish lacks mature experimental models and cell lines, gene knockout or overexpression experiments are difficult; on the other hand, the whole genome of snakehead fish has just been finely assembled (Sun et al., 2024), and functional research technology platforms such as gene editing are still under establishment. 3 Mining and Functional Study of Key Genes for Disease resistance in Snakehead Fish 3.1 Methods for screening candidate disease resistance genes For non-model fish such as snakehead fish, screening of candidate disease resistance genes usually relies on large-scale omics analysis and comparative experiments. Whole genome scanning is a powerful means, such as constructing a family for linkage analysis or performing a genome-wide association study (GWAS) on a population to find gene loci associated with disease resistance phenotypes (Fraslin et al., 2020). Gene family screening is another strategy, which is to search and identify homologous sequences in the snakehead fish genome based on known immune-related genes in other species. For example, through sequence alignment, Han et al. (2025a) successfully identified all members of the IL-17 family in the snakehead fish genome and further analyzed their expression patterns. For another example, through Hidden Markov Model search, researchers found all gene sequences of the snakehead fish NLR family (Zhu et al., 2025). Traditional candidate gene methods have also played a certain role, such as directly selecting some key factors for snakehead fish sequence cloning and detection based on existing fish immunity knowledge.
RkJQdWJsaXNoZXIy MjQ4ODYzNA==