A Comparative Study on Growth and Metabolism of Eriocheir sinensis Juveniles Under Chronically Low and High pH Stress

Xiaodan Wang,Chunling Wang,Liqiao Chen,Changle Qi,Zhimin Gu,Zhipeng Huang,Erchao Li,Jian G Qin

doi:10.3389/fphys.2020.00885

Abstract

This study elucidates the effects of chronic pH stress on the growth and metabolic response of juvenile Chinese mitten crab Eriocheir sinensis. Crabs were exposed under normal pH (control, pH = 8.0 ± 0.20), low pH (pH = 6.5 ± 0.20), and high pH (pH = 9.5 ± 0.20) in an 8-week trial. Both low and high pH suppressed weight gain but low pH had more adverse effects. No difference was observed on survival, crude lipid, and protein. Acidic stress significantly reduced protein efficiency. The malondialdehyde (MDA) content in hepatopancreas was highest at low pH. The superoxide dismutase (SOD) activity in hepatopancreas and total hemocyte counts (THC) in the stress groups were higher than that in the control. Crabs under high pH had the highest ACP and AKP activities, but there was no significant difference between the control and low pH groups. In the transcriptome analysis, 500.0M clean reads were obtained from the control, low pH, and high pH groups, and assembled into 83,025 transcripts. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were analyzed to obtain the significantly changed pathways involving differently expressed genes. Ten and eight pathways in metabolism were significantly changed in low pH vs control and high pH vs control groups, respectively. According to the reported functions of these pathways, most of them participated in carbohydrate metabolism. The metabolism pathway analysis indicates the increases of stress resistance, glucose metabolism, and molting activities under chronically pH stress. This study suggests that low pH has more negative impact on crab growth, and oxidative phosphorylation is the main source of energy source under low pH stress, while aerobic glycolysis supplies most energy under high pH stress.

Highlights

Unlike seawater, freshwater has poor buffering capacity and can experience a wider range of pH fluctuation (Han et al, 2016)
The protein efficiency rate (PER) at low pH was lower than the control and the high pH group (Figure 1D), but there was no difference between the control and high pH group
The MDA content in hepatopancreas was highest in the pH 6.5 group and there was no significant difference between the control group and high pH group (Figure 2A)

Summary

Introduction

Freshwater has poor buffering capacity and can experience a wider range of pH fluctuation (Han et al, 2016). The level of pH in aquaculture pond fluctuates from 6.6 to 10.2 because carbon dioxide is removed by plants and algae through photosynthesis at daytime while carbon dioxide is released through respiration in the water at night (Li and Chen, 2008). The exposure of freshwater organisms to an abnormal pH can lead to mortality and reduction in growth and reproduction (Kim et al, 2015). An acidic environment can reduce the pH in blood or hemolymph in aquatic animals, resulting in low oxygen carrying capacity and physiological hypoxia (Han et al, 2018a). Alkaline stress would corrode the gills of aquatic animals, leading to the reduction of ion absorption and mortality (Qian et al, 2012). Though crustaceans have the ability to adapt to pH change in a certain range, it is evident that extreme pH especially lower pH would trigger abnormal functions in physiological, molecular, and biochemical pathways (Chen et al, 2015; Kawamura et al, 2015; He et al, 2019)

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