International Journal of Aquaculture, 2024, Vol.14, No.2, 81-90 http://www.aquapublisher.com/index.php/ija 82 2 Genomic Insights into Largemouth Bass 2.1 Genome structure and organization The genomic structure and organization of largemouth bass (Micropterus salmoides) have been explored to understand the genetic basis of various physiological traits. The Dmrt1 gene, which plays a crucial role in sex determination and differentiation, has been identified and characterized in largemouth bass. The Dmrt1 gene consists of five exons and four introns, and its expression is highly conserved and exhibits significant gender dimorphism, being highly expressed in the testis of mature fish but only weakly expressed in other tissues (Yan et al., 2019). This gene's structure and expression patterns provide insights into the genetic mechanisms underlying sex differentiation in largemouth bass. 2.2 Key genes involved in growth Several studies have identified key genes involved in the growth of largemouth bass. For instance, the metabolic adaptation to high-starch diets involves the up-regulation of genes related to fatty acid and TAG synthesis and the down-regulation of genes related to TAG hydrolysis and β-oxidation. This indicates that largemouth bass can adapt to dietary changes by modulating the expression of genes involved in metabolism (Chen et al., 2022). Additionally, nutritional programming at early developmental stages can significantly impact growth and dietary plant protein utilization, with specific programming windows leading to improved growth and protein utilization (Schwepe et al., 2022). These findings highlight the importance of specific genes and developmental stages in the growth regulation of largemouth bass. 2.3 Genes related to environmental adaptation Largemouth bass exhibit remarkable adaptability to various environmental stressors, which is mediated by specific genes. For example, exposure to high environmental ammonia (HEA) triggers the up-regulation of Rhesus (Rh) glycoproteins, which play a role in ammonia excretion, and the activation of ion-regulatory and metabolic pathways to mitigate ammonia toxicity (Egnew et al., 2019). Similarly, intermittent hypoxic exposure promotes liver vascular remodeling through the regulation of angiogenesis-related genes, such as Jagged, PI3K, and MAPK, enhancing hypoxia tolerance (Yan et al., 2023). Additionally, microRNA regulation under hypoxic conditions involves the differential expression of miRNAs and their target genes, which are enriched in pathways like VEGF and MAPK signaling, contributing to the hypoxic stress response (Sun et al., 2020). These studies underscore the genetic basis of environmental adaptation in largemouth bass, involving a complex interplay of various genes and regulatory mechanisms. 3 Developmental Mechanisms 3.1 Growth regulation pathways Growth in largemouth bass (Micropterus salmoides) is regulated by a complex interplay of genetic and molecular pathways. Key pathways include the growth hormone–insulin-like growth factor 1 (GH-IGF1) axis, glycolysis, and the myostatin/transforming growth factor beta (TGF-β) signaling pathways. These pathways are crucial for muscle growth and overall development. For instance, RNA sequencing has identified several genes involved in these pathways, such as phosphoenolpyruvate carboxykinase 1, FOXO3b, and heat shock protein beta-1, which are associated with growth traits in largemouth bass (Li et al., 2017). Additionally, selective breeding and domestication have led to the identification of candidate genes like psst1 and grb10, which are linked to growth and early development (Sun et al., 2023). 3.2 Hormonal control of development Hormonal regulation plays a pivotal role in the development of largemouth bass. Hormones such as estradiol (E2) and vitellogenin (VTG) are critical for ovarian development and overall reproductive health. Studies have shown that environmental chemicals can disrupt these hormonal pathways, leading to altered gene expression and physiological endpoints. For example, quercetin and tretinoin have been identified as potential endocrine disruptors that significantly alter the expression of reproductive-associated genes in largemouth bass (Basili et al., 2018). Furthermore, the GH-IGF1 axis is also influenced by hormonal signals, which regulate growth and metabolic processes (Li et al., 2017).
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