International Journal of Aquaculture, 2024, Vol.14, No.3, 139-153 http://www.aquapublisher.com/index.php/ija 146 salinity stress. Such differential expression analysis helps to identify key genes associated with salinity tolerance, thereby providing a theoretical basis for the conservation and aquaculture of these species (Adapted from Rahi et al., 2019) Figure 2 Heatmap showing differential expression pattern of transcripts at 0 & and 15 & salinities for three different Macrobrachium species (Adopted from Rahi et al., 2019) Image caption: (a) M. australiense (876 transcripts), (b) M. tolmerum(861 transcripts), and (c) M. novaehollandiae (925 transcripts) (Adopted from Rahi et al., 2019) 6.3 Comparative analysis Comparing adaptation mechanisms in marine and freshwater species reveals both commonalities and unique strategies. Both environments require species to develop efficient osmoregulation mechanisms to cope with salinity variations. For instance, both Gulf killifish and freshwater prawns exhibit genetic adaptations related to ion transport and osmoregulation, highlighting the convergent evolution of these traits in response to salinity challenges (Oziolor et al., 2019; Rahi et al., 2019). However, differences arise in the specific environmental pressures and adaptive responses. Marine species often face greater challenges related to hypoxia and pressure, as seen in cetaceans, which have evolved unique genetic adaptations for efficient oxygen use and deep diving capabilities (Tsagkogeorga et al., 2015). In contrast, freshwater species like the Tibetan Schizothoracinae fish primarily adapt to temperature and oxygen fluctuations at high altitudes, with genetic changes focusing on energy metabolism and immune response (Tong et al., 2017). Overall, the study of adaptation in aquatic species underscores the importance of both phenotypic plasticity and genetic evolution in enabling species to survive and thrive in diverse and changing environments. Figure 3 illustrates the immune characteristics of Schizothoracine fish (G. p. ganzihonensis), including their innate immune system and Toll-like receptor (TLR) signaling pathway, as well as the mortality rates from two major infectious diseases. Panel (a) shows a schematic diagram of the innate immunity and the TLR signaling pathway in Schizothoracine fish. Four positively selected genes (PSGs) are highlighted in the TLR pathway: TLR3, IL10, IRF8, and TNFRSF1b. The innate immune response of these fish to pathogen invasion involves four major families: TLRs (Toll-like receptors), ILs (interleukins), IRFs (interferon regulatory factors), and TNFs (tumor necrosis factors). When a pathogen invades, genes from these families are activated to initiate an immune response to combat the infection. TLR stands for Toll-like receptor, IL stands for interleukin, IRF stands for interferon regulatory factor, and TNF stands for tumor necrosis factor. Panel (b) displays the mortality rates of Schizothoracine fish due to two major infectious diseases: white spot disease and saprolegniasis. The bar graph indicates that the mortality rate for white spot disease is nearly 100%, whereas the mortality rate for saprolegniasis is also high but slightly lower than that of white spot disease. These results suggest that Schizothoracine fish have
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