Effect of glutamine and cysteine supplementation on quality of cryopreserved sperm of South American silver catfish

The aim of this study was to investigate the effects of different concentrations of glutamine (experiment 1) and glutamine + cysteine (experiment 2) on post‐thaw sperm quality of South American silver catfish (Rhamdia quelen). The sperm was cryopreserved in cryoprotectant solution (fructose 50 g/L, powdered milk 50 g/L and methanol 100 ml/L) containing different glutamine concentrations (0, 2.5 and 5 mM; experiment 1) and a combination of glutamine (2.5 and 5 mM) and cysteine (2.5 and 5 mM; experiment 2). In experiment 1: glutamine supplementation groups increased DNA fragmentation; the concentration of carbonyl groups was lower and the concentration of sulfhydryl groups was higher in control; a higher activity of superoxide dismutase (SOD), catalase (CAT), glutathione‐S‐transferase (GST) and glutathione peroxidase (GPx) enzymes was observed in the 2.5 and 5 mM groups. In experiment 2: the group with 5 mM of cysteine +5 mM of glutamine presented the higher DNA damage; treatments with 5 mM of glutamine presented the higher concentration of carbonyl groups and a higher activity of CAT and GST. The findings of this study show that glutamine and cysteine, at the concentrations evaluated in this study, does not present satisfactory results but rather damaging effects on sperm quality of R. quelen.