Impact of hypoxia to the catfish industry
Oxygen is important for aerobic organisms, especially for fish who live in the aquatic environment with routinely low dissolved oxygen (Wang et al., 2017b). Under aquaculture conditions, hypoxia can be caused by natural phenomena (e.g., weather, temperature, or water flow rate), water pollution and eutrophication, high stocking density, and improper use of aeration (Green et al., 2016; Wu, 2002; Zhang et al., 2010). In spite of the strong tolerance of catfish to low oxygen, hypoxia can still lead to huge economic losses. Exposure to low oxygen stress can affect the growth rate (Mallya, 2007), feed conversion rate (Buentello et al., 2000), and increase the susceptibility to infectious diseases of catfish …show more content…
However, opposite observations were also made (Rex Dunham, Auburn University, personal communication). In one experiment, the tolerance to low dissolved oxygen of six strains in channel catfish, including 103KS strain, Kansas strain, KMix strain, Marion strain, Marion S strain, and Thompson strain, was evaluated (Wang et al., 2017a). Compared with other strains, two channel catfish strains (103KS strain and Marion S strain) exhibited higher tolerance to low oxygen stress, whereas Marion strain of channel catfish showed the lowest tolerance to hypoxia stress (Wang et al., 2017a). Compared with channel catfish and blue catfish, interspecific hybrid catfish (female channel catfish×male blue catfish) exhibited higher tolerance to low oxygen (Dunham et al., 1983). The strains of their parents were demonstrated to have an effect on the tolerance of hybrid catfish to low oxygen (Dunham et al., 2014). For instance, hybrid catfish sired by Rio Grande (Texas) strain exhibited better tolerance to low oxygen than the hybrid catfish sired by Alabama strains at 26°C (Dunham et al., 2014). However, at lower temperatures (9 °C and 17 °C), hybrid catfish sired by Alabama strains showed the highest tolerance to low dissolved oxygen than other channel catfish strains (Dunham et al., …show more content…
For instance, the major regulator of low oxygen stress, HIF-1α, has been discovered to function as a key regulator of macrophage and neutrophil inflammatory and innate immunity (Zinkernagel et al., 2007). The potential linkage between immune responses and the responses to hypoxia were also observed in catfish. After infection with high challenge dose of E. ictaluri, channel catfish in the hypoxic groups had significantly higher mortality (approximately 36%) than the catfish in control groups (approximately 12%) (Welker et al., 2007). Furthermore, PI3K signaling pathway was found to be involved in the responses to both hypoxia stress and bacterial infections, as supported by GWAS analysis of tolerance to low oxygen in channel catfish (Wang et al., 2017b) and hybrid catfish (Zhong et al., 2017), and columnaris resistance in hybrid catfish (Geng et al., 2015). Many of annotated genes within the QTL associated with hypoxia tolerance and columnaris resistance were involved in PI3K signaling pathway (Geng et al., 2015; Wang et al., 2017b; Zhong et al., 2017), suggesting that PI3K signaling pathway was both important for response to hypoxia and bacterial infection. Similarly, members in several gene families (e.g. receptor tyrosine kinases, claudin genes, bcl-2 genes, CC and CXC chemokine families) were both regulated after bacterial infection or hypoxia stress (Fu et