International Journal of Aquaculture, 2024, Vol.14, No.2, 51-61 http://www.aquapublisher.com/index.php/ija 52 pathways associated with disease resistance in carp and evaluates the effectiveness of different breeding strategies. The study also discusses future prospects and challenges. By providing a comprehensive review of the current state of molecular breeding for disease resistance in carp, this study aims to inform future studies and guide the development of more resilient aquaculture systems. 2 Overview of Disease Resistance in Common Carp 2.1 Major diseases affecting common carp Common carp (Cyprinus carpio L.) are susceptible to a variety of diseases that can significantly impact aquaculture productivity. Among the most notable diseases are those caused by bacterial pathogens such as Aeromonas hydrophila, which leads to motile aeromonad septicaemia (MAS) (Jeney et al., 2011; Liu et al., 2014), and viral infections like Cyprinid herpesvirus-3 (CyHV-3), also known as koi herpesvirus(KHV) (Palaiokostas et al., 2018a; Palaiokostas et al., 2019). Additionally, carp are affected by various parasites, mainly including Dactylogyrus, Trichodina, and copepod parasites (Obaid et al., 2021). These diseases can lead to high mortality rates and cause substantial economic losses in carp farming. 2.2 Traditional breeding approaches Traditional breeding approaches for disease resistance in common carp have primarily involved selective breeding, crossbreeding, and hybridization. Selective breeding has been used to enhance resistance to specific diseases, such as dropsy, through long-term selection programs. Crossbreeding and hybridization have also been employed to combine desirable traits from different strains, leading to improved growth rates and disease resistance (Vandeputte et al., 2003). For instance, the Krasnodar common ca. 2.3 Limitations of conventional methods Despite the successes of traditional breeding methods, there are several limitations. Conventional breeding approaches often require long timeframes to achieve significant genetic improvements and may not always result in the desired level of disease resistance. Additionally, the genetic basis of disease resistance is complex and influenced by multiple genes, making it challenging to achieve consistent results through traditional methods alone (Vandeputte et al., 2003). Furthermore, environmental factors can introduce biases in heritability estimates, complicating the selection process (Vandeputte et al., 2003). The need for more precise and efficient breeding techniques has led to the exploration of molecular breeding methods, which offer the potential to overcome these limitations and accelerate the development of disease-resistant common carp. 3 Marker-Assisted Selection (MAS) 3.1 Principles and applications of MAS Marker-Assisted Selection (MAS) is a molecular breeding technique that utilizes DNA markers to select for desirable traits in organisms, such as disease resistance in common carp. The primary principle of MAS is to identify and use molecular markers that are closely linked to genes of interest, thereby enabling the selection of individuals carrying these genes without the need for phenotypic screening. This approach significantly accelerates the breeding process by allowing early and accurate selection of desirable traits (Banu et al., 2017; Eze, 2019). MAS has been successfully applied in various breeding programs, particularly for traits with simple inheritance patterns. For instance, in crop plants, MAS has been used to introgress resistance genes into elite cultivars, thereby enhancing disease resistance and improving overall crop performance (Eze, 2019). Similarly, in nematode resistance breeding, MAS has facilitated the rapid and objective identification of resistant plant accessions, streamlining the breeding process (Banu et al., 2017). 3.2 Advantages over traditional methods MAS offers several advantages over traditional breeding methods. Firstly, it reduces the time and resources required for breeding by enabling early selection of desirable traits. Traditional breeding often involves lengthy and labor-intensive processes of phenotypic screening, which can be bypassed using MAS (Eze, 2019; Banu et al., 2017).
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