Temporal variations in glucose level, oxidative stress and antioxidant profile of Koi carps (Cyprinus carpio var koi) in response to hypoxic tolerance

Biochemical analyses were conducted temporally to understand the impact of prolonged hypoxic environment on gill and white muscle of juvenile Koi carps (Cyprinus carpio var koi). The 16-day study involved quantification of Glucose (GLU), oxidative stress (Lipid Peroxidation-LPO) and antioxidant profile (Catalase-CAT, Glutathione-GSH, Glutathione-S-Transferase-GST) every 96th hour to understand the physiological consequences of hypoxic environment compared to normoxia (Control). There was no mortality throughout the study period, however, fishes were physically exhausted and exhibited Aquatic Surface Respiration (ASR) after day 8. Reduction in glucose levels was observed for both the tissues from day 4 to 16. LPO values increased in gill from day 4 to 12 followed by decrease on day 16. Catalase values reduced in gill from day 4 to 12 with an abrupt spike on day 16. Among the glutathione antioxidants, negligible GST activity was observed for day 12 and 16 in gill and muscle, while day 4 and 8 revealed fluctuations in GSH for both the tissues. The study showed tissue-specific differential response to stress because of a variance in the evaluated biomarkers in gill and muscle. Understanding the extent of physiological response to progressive oxygen disruption is essential for best practices in pisciculture because its availability is a critical factor impacting fish health which is congruent to the results of this study.