International Journal of Molecular Veterinary Research, 2025, Vol.15, No.1, 43-50 http://animalscipublisher.com/index.php/ijmvr 46 4.3 Gene-environment interactions influencing disease resistance in tilapia Environmental factors, such as water temperature and microbiota status, play an important role in modulating tilapia disease resistance molecular mechanisms. Temperature elevation is likely to increase S. agalactiae virulence and disturb intestinal microbiota, which causes impaired immune resistance and mortality. Environmental stresses and genetic background together control levels of gene expression, immune pathway activation, and immune response function. These interactions among environmental and genetic factors highlight the need to consider both environmental and genetic factors in tilapia breeding and disease resistance management programs (Wonmongkol et al., 2018; Oviedo-Bolaños et al., 2021). 5 Breeding and Selection Strategies for Disease-Resistant Tilapia 5.1 Application of traditional family selection and hybrid breeding in tilapia Traditional family selection, where families are evaluated and chosen depending on the performance of individuals for disease resistance and other traits, has been used intensively in tilapia breeding schemes. The approach has demonstrated considerable genetic gains for resistance to diseases caused by pathogens such as Streptococcus agalactiae and TiLV, with heritability for disease resistance traits found to be moderate to high. Hybridization, through crossing different tilapia strains or species, also has the potential to enhance disease resistance due to heterosis and specific immune response. Both these strategies have been used in commercial breeding programs, with resultant enhancement of survival rates and reduced losses due to disease with no adverse effect on growth performance (Suebsong et al., 2019; Abwao et al., 2021). 5.2 Research progress of marker-assisted selection (MAS) in disease-resistant tilapia breeding Marker-assisted selection (MAS) exploits molecular markers linked to disease resistance genes or quantitative trait loci (QTLs) for speeding up resistance breeding for resistant strains. Microsatellite and SNP markers linked to major pathogens' resistance have recently been identified, which can be employed in selection for resistant individuals without pathogen challenge. MAS has been known to reduce offspring mortality rates from resistant parents significantly, thereby establishing its viability and effectiveness in tilapia breeding programs. Implementation of predictive models based on marker genotypes also enhances the effectiveness and precision of MAS (Vela-Avitúa et al., 2023). 5.3 Prospects of genomic selection (GS) for improving disease resistance traits in tilapia Genomic selection (GS) uses genome-wide markers to better predict breeding values for disease resistance with higher accuracy and at faster genetic progress than in traditional or in MAS schemes. GS was applied successfully in tilapia, and GBLUP and BayesB had superior performance over pedigree-based methods in the prediction of resistance to Streptococcus agalactiae and TiLV. Polygenic disease resistance in tilapia is what makes GS particularly suitable, given that it portrays the effect of many minor-effect loci. The use of GS in breeding schemes is likely to accelerate further the production of healthy, disease-resistant tilapia lines (Lu et al., 2020; Barría et al., 2021; Sukhavachana et al., 2020; 2021) (Figure 2). 5.4 Potential of gene editing and emerging biotechnologies in tilapia disease resistance research New biotechnologies, including gene editing technologies such as CRISPR/Cas9, hold immense potential to enhance tilapia disease resistance. While early-stage practical uses exist presently, the technologies promise to make direct modification or introduction of resistance genes feasible to complement traditional and genomic selection methods. Innovations in functional genomics and reverse vaccinology technology are also illuminating the path to the identification of novel resistance genes and vaccine antigens, providing scope for novel disease control measures in tilapia aquaculture (Barría et al., 2021). 6 Evaluation and Promotion of Disease-Resistant Tilapia Strains 6.1 Phenotypic assessment and challenge test methods for disease resistance Phenotypic tests for disease resistance in tilapia typically entail controlled challenge tests, where the fish are exposed to a known pathogen such as Streptococcus agalactiae or Tilapia Lake Virus (TiLV) under pond or laboratory conditions. They are observed for survival, clinical status, and immune response to ascertain resistance. For example, types of cohabitation and laboratory challenge tests have been utilized for quarantining resistant and
RkJQdWJsaXNoZXIy MjQ4ODYzNA==