Oxygen limitation and tissue metabolic potential of the African fish Barbus neumayeri: roles of native habitat and acclimatization

Acclimatization to the low DO site resulted in lower growth rates, lower activities of the aerobic enzyme CCO in heart, and higher activities of the glycolytic enzyme PFK in heart and skeletal muscle. The activity of LDH in liver tissue was correlated with site of origin, being higher in fish collected from a hypoxic habitat, regardless of acclimatization treatment.Our results suggest that the influence of site of origin and hypoxic acclimatization in determining enzyme activity differs among enzymes and tissues, but both factors contribute to higher glycolytic capacity and lower aerobic capacity in B. neumayeri under naturally-occurring conditions of oxygen limitation.Because the concentration of dissolved oxygen (DO) in water is influenced by many factors, including temperature, depth, salinity, and eutrophication, organisms living in aquatic environments can be subjected to temporal and spatial variation in DO. Among fishes, low levels of DO, or hypoxia, is associated with impaired growth and reproduction [1-3]. If severe, hypoxia can lead to high rates of mortality in fish and other aquatic organisms depending upon their degree of hypoxia tolerance [4-6]. Aquatic hypoxia is a major environmental stressor that has become a global issue [7,8], and some predictions suggest that current global climate change will further exacerbate the problem [9,10]. Thus, it has become increasingly important to understand mechanisms that fish use in order to persist and survive under hypoxia.Intraspecific variability in physiological traits plays a key role in the capacity of fish to adjust to low oxygen. Such variability can be attributed to genetic differentiation, phenotypic plasticity, or a combination of both. The time course of phenotypic responses to low oxygen varies from minutes or hours (e.g., acute responses) to days or weeks (development, acclimation, and acclimatization). Depending on the duration and intensity of hypoxia exposure, fish may display adjustments at beha