Physiological and molecular responses of a bottom dwelling carp, Cirrhinus mrigala to short-term environmental hypoxia.

Abstract

An experiment was conducted to monitor temporal changes in the gene expression of a specific molecular marker, HIF-1a in response to a 15-day exposure to chronic hypoxia in a bottom dwelling carp, Cirrhinus mrigala. The expression level of HIF-1a mRNA was increased in gills of C. mrigala in response to 0.5 mg/L, dissolved oxygen (DO) for 15 days with the time of exposure, whereas it remained unchanged in fishes exposed to normoxia (DO, 6.5 mg/L). Based on the first experiment it is found that HIF is expressed at moderate level 72 hours, and it peaks at 7 and 15 days, indicating that 72 h is a tolerable time limit for survival under hypoxia for the particular species. Thus, a second experiment was conducted to evaluate the effect of hypoxia (0.5 mg/L) for 72 h and assessed different parameters such as metabolic enzymes, antioxidant enzymes and haematological parameters. The haematological parameters, such as RBC count, Hb and Hct values increased significantly (P<0.05) during exposure to hypoxia. Metabolic enzyme activities, especially the enzymes of the anaerobic glucose metabolism, such as HK, LDH and G6pase activities and the antioxidant enzymes, such as SOD, CAT and GPX activities have also revealed increasing trend in hypoxic conditions. We conclude that 72 h under acute hypoxia (0.5 mg/L) is sufficient to potentiate haematological, metabolic and antioxidant responses and the tolerance to hypoxia in mrigal is mediated by the activation of the transcription factor, HIF-1α. © Published by Central Fisheries Research Institute (CFRI) Trabzon, Turkey.