Abstract
Ammonia stress can inhibit the survival and growth, and even cause mortality of shrimp. In this study, ammonia-metabolizing enzyme activities and gene expression were compared between two strains of L. vannamei under different ammonia-N () concentrations (3.4, 13.8, and 24.6 mg/L). The results showed that elevated ammonia concentrations mainly increased glutamine synthetase (GSase) activities while inhibiting transglutaminase (TGase) activities in the muscle of both strains. Thus, we concluded that L. vannamei could accelerate the synthesis of glutamine from glutamate and to alleviate ammonia stress. Compared with the muscle, the hepatopancreas plays a major role in ammonia stress and might be a target tissue to respond to the ammonia stress. Compared to the control group, the treatment of high ammonia concentrations reduced the hepatopancreas TGase (TG) gene expression and increased the gene expression rates of glutamate dehydrogenase-β (GDH-β) and GSase (GS) in both the muscle and the hepatopancreas of the two strains (p < 0.05). These genes (GDH-β and GS) in strain B were not only expressed earlier but also at levels higher than the expression range of strain A. At the gene level, strain B showed a more rapid and positive response than strain A. These data might help reveal the physiological responses mechanisms of shrimp adapt to ammonia stress and speed up the selective breeding process in L. vannamei.
Highlights
Due to its high commercial value, the white-legged shrimp (Litopenaeus vannamei, Boone, 1931) has been widely cultured throughout the world (Wu et al, 2008)
Compared with strain A, strain B could stimulate the activity of ammonia metabolizing enzymes in an earlier stage, which plays an important role in maintaining the stability of the content of ammonia-N in shrimp
The IBR demonstrated that, compared to the muscle, the hepatopancreas is more sensitive to ammonia stress and the hepatic tissue might be the main tissue that causes the different responses in the two strains
Summary
Due to its high commercial value, the white-legged shrimp (Litopenaeus vannamei, Boone, 1931) has been widely cultured throughout the world (Wu et al, 2008). Previous studies have shown that various tissues of L. vannamei had been seriously affected when exposed to different ammonia stress levels (Racotta and Hernández-Herrera, 2000; Liang et al, 2016; Liu et al, 2016; Zhou et al, 2017). Few studies have investigated ammonia-metabolizing enzymes in different tissues of local strains of L. vannamei in response to ammonia stress. To explore the metabolic responses mechanism of L. vannamei under the ammonia stress, two shrimp strains with different susceptibility to ammonia were evaluated in this study. The activity of three ammoniametabolizing enzymes, including glutamate dehydrogenase (GDHase), glutamine synthetase (GSase), transglutaminase (TGase), and their gene expression (GDH-β, GS, and TG) were investigated in muscle and hepatopancreas tissues under exposure to different ammonia levels
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