Abstract
In this study, metabolic responses of Persian sturgeon fingerlings to hyperosmotic
condition were investigated by NMR-based metabolomics. Persian sturgeon fingerlings
(n = 2010, mean total weight: 3.2 0.6 g; mean total length: 8.5 1.5 cm)
were held in freshwater (FW) for 96 hr and then acclimated in brackish water (BW)
(12 g/L) for 24 hr. Blood samples were taken before and after salinity acclimation.
The major metabolite changes corresponding to salinity acclimation were related to
amino acids, osmolytes and energy metabolites. The plasma glucose levels increased
significantly after 24 hr acclimation in BW (p < .05). Other energetic metabolites
(acetate, acetoacetate, beta-hydroxybutyrate, phosphocreatine, creatine, glycerol)
showed no significant changes after 24 hr salinity challenge (p > .05). The osmolytes
(taurine, trimethylamine-N-oxide, choline, N,N-dimethylglycine) and amino acids (aspartate,
glutamate, glutamine, leucine, phenylalanine, b-alanine, histidine, threonine,
cysteine) declined significantly after 24 hr acclimation in BW (p < .05). However,
the levels of glycine elevated after 24 hr acclimation in BW (p < .05). Other amino
acids including aspargine, isoluecine, Tyrosine, Tryptophan, Valine, and Lysine
showed no significant changes after salinity challenge (p > .05). The considerable
decreases in almost all plasma amino acids and all osmolytes showed specific importance
of these metabolites in osmotic adaptation of fish in BW. Also, it seems that
Persian sturgeon fingerlings rely more on oxidation of glucose to meet energetic
requirements of osmoregulation than oxidation of lipids, as we observed no detectable
changes in metabolites associated with lipid oxidation during osmotic acclimation
in BW. Our results may help to understand osmoregulation in a chondrostei
fish species from a metabolic approach.