A STUDY ON MOLECULAR RESPONSES OF HYPOXIA EXPOSURE IN GOLDEN MAHSEER, Tor putitora (HAMILTON, 1822)
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Date
2023-10-01
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G.B. Pant University of Agriculture and Technology, Pantnagar-263145
Abstract
Golden mahseer is an important food and recreational species of Indian Himalayan
region and also declared as an endangered species. The present study aimed to observe the
behavioural, metabolic and molecular response of golden mahseer to acute hypoxia. The
fishes were exposed to 96 hour of hypoxia stress. Different parameters related to behavioral
and metabolic responses were documented. The molecular response was studied by qRTPCR
assay of 12 hypoxia responsive genes hif1ab, hif2a, hif3a, aldoaa, vegfaa, vegfab,
ldhb1, igfbp-1, igfbp-2a, igfbp-3, epoa, hmox2a. Under hypoxia stress fish showed
behavioural responses in terms of aerial emergence, rapid gulping, circular swimming,
wide-mouth gape, settling at the bottom corner and rapid tail movement. The gill
ventilation rate increased with decreasing dissolved oxygen level that indicated that the
fishes equilibrate the oxygen pressure in the blood with the oxygen pressure in the
surrounding water. The mass specific consumption rate of oxygen significantly decreased
which showed the metabolic response under low oxygen availability. The distinctive
expression pattern of hif2a and hif3a mRNA indicated its role in adaptive response to tissue
hypoxia. Among the vascular endothelial growth factor genes the enhanced expression of
vegfab across all examined tissue of Tor putitora suggests its role in the adaptation to acute
hypoxic stress. Among different igfbp’s only igfbp1 have shown enhanced expression in
different tissues while igfbp2a and igfbp3a did not expressed under hypoxic condition. The
detection of only one isoform (igfbp1) of golden mahseer suggested that it predominantly
regulate the igfbp function in this species. The up-regulation of erythropoietin a (epoa)
gene in different tissue of Tor putitora suggests its role in haemoglobin oxygen affinity in
maintaining the haemoglobin saturation under falling blood oxygen level conditions. The
heme oxygenase 2 alpha (hmox2a) expression in different tissue under hypoxic condition
suggested its role in iron homeostasis under stress condition. The ldhb1 and aldoaa are
metabolic genes which are involved in glycolytic pathway. The up-regulation of ldhb1 and
aldoaa is indicative of activation of anaerobic glycolysis in response to hypoxic stress as an
adaptation mechanism under low oxygen availability. The present study provides valuable
information regarding the molecular response of different genes to hypoxia stress in golden
mahseer. These genes can also be used as the biomarkers of ecosystem hypoxia stress.
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