Respiratory plasticity during acclimation to hypoxia and following a recovery in normoxia

Abstract

Phenotypic plasticity manifested after acclimatization is a very important source of biological variability among fish species. We hypothesized that hypoxic acclimation, besides potentially generating a temporary hypoxic respiratory phenotype, would also manifest as a continued benefit after reacclimation to normoxia. Hence, we holistically characterized the respiratory phenotype of European sea bass ( Dicentrarchus labrax (Linnaeus, 1758)) acclimated to normoxia with or without prior acclimation to hypoxia. Compared with the original normoxic phenotype, prior acclimation to hypoxia and return to normoxia produced a 27% higher absolute aerobic scope (AAS), a 24% higher citrate synthase activity in red muscle, and a 28% lower excess post exercise O2 consumption. Additional testing of hypoxia-acclimated fish under normoxia explored the specific effects of hypoxic acclimation. The hypoxic phenotype, when compared with the original normoxic phenotype, had a lower standard metabolic rate, a better hypoxia performance, and a lower minimum PO2 for supporting 50% AAS. Thus, respiratory plasticity allows sea bass to improve its maximum aerobic capacity after returning to normoxia from hypoxic acclimation, a potential benefit from exploiting a hypoxic habitat. Given this respiratory malleability, general predictions for marine fish exploiting a more hypoxic future should better consider respiratory plasticity and prolonged effects of hypoxic exposures.