Abstract
The Paramisgurnus dabryanus was exposed to air to assess the changes in plasma, liver and muscle free amino acid (FAA) contents. The FAA concentrations in plasma, liver and muscle of P. dabryanus were significantly affected by aerial exposure (P < 0.05). After 12 h of aerial exposure, the plasma glutamate contents increased significantly (P < 0.05) and reached peak value at 24 h of air exposure. With increasing air exposure time, the plasma alanine contents increased significantly and more dramatically than the control values (P < 0.05). From 24 to 48 h of aerial exposure, the liver free glutamate contents increased significantly and reached the peak value at 48 h of air exposure (P < 0.05). The liver free alanine contents in air exposure group were markedly higher than these values in the control group (P < 0.05). After 72 h of air exposure, the muscle free glutamate contents increased markedly (P < 0.05) and were significantly higher than the control values (P < 0.05). The muscle free alanine contents remained at constant values during the first 12 h of aerial exposure (P > 0.05), thereafter, these concentrations increased significantly until the end of experiment (P < 0.05). Our results showed that glutamate and NH4+ could be used to synthesize glutamine via glutamine synthetase to convert internal ammonia into non-toxic glutamine in P. dabryanus during air exposure. Furthermore, the P. dabryanus could catabolize several certain amino acids, leading alanine form to reduce endogenous ammonia production. The decrease in tissue free glutamate, arginine and proline in P. dabryanus indicated that these certain amino acids should be the starting substrate to be converted to alanine and energy.
Highlights
IntroductionAmmonia is toxic to aquatic animals (Zhang et al, 2017c) causing a decrease in growth and food intake (Naqvi et al, 2007; Paust et al, 2011), tissue damage (Rodrigues et al, 2011), gill morphological change (Dong et al, 2013), gill remodeling (Sinha et al, 2014), cell apoptosis and oxidative stress (Cheng et al, 2015; Pinto et al, 2016; Zhang et al, 2018)
Obvious increases inplasma, liver and muscle free alanine contents in P. dabryanus were observed during different periods of aerial exposure
The decrease in tissue free glutamate, arginine and proline in P. dabryanus indicated that these certain amino acids should be the starting substrate to be converted to alanine and energy
Summary
Ammonia is toxic to aquatic animals (Zhang et al, 2017c) causing a decrease in growth and food intake (Naqvi et al, 2007; Paust et al, 2011), tissue damage (Rodrigues et al, 2011), gill morphological change (Dong et al, 2013), gill remodeling (Sinha et al, 2014), cell apoptosis and oxidative stress (Cheng et al, 2015; Pinto et al, 2016; Zhang et al, 2018). Some air-breathing fish, like Paramisgurnus dabryanus (Zhang et al, 2017b), Misgurnus anguillicaudatus (Chew et al, 2001; Tsui et al, 2004), Monopterus albus (Ip et al, 2004), Boleophthalmus boddaerti, and Periophthalmodon schlosseri (Ip et al, 2005), can accumulate quite high levels of endogenous ammonia For these species, several ammonia detoxification strategies have been demonstrated to help deal with excessive endogenous ammonia loading, such as less toxic glutamine and urea synthesis (Sanderson et al, 2010; Loong et al, 2012), active NH4+ excretion (Tay et al, 2006), ammonia detoxification improved by Rhesus glycoproteins and aquaporins (Edwards et al, 2015; Chng et al, 2016), lowering of ambient pH (Chew et al, 2003a), NH3 volatilization and alkalization of body surface (Tsui et al, 2004), reduction in body ammonia production (Loong et al, 2012) and certain types of amino acid catabolism leading to alanine form (Sinha et al, 2013)
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