Exposure to neodymium blunts the hypoxic ventilatory response in fathead minnows

In hypoxia, the initial response in vertebrates is hyperventilation, known as the Hypoxic Ventilatory Response (HVR), which is a physiological reflex that allows fish to maintain adequate oxygen uptake to meet metabolic demands. The severity of hypoxia in aquatic ecosystems is growing due to anthropogenic impacts. This is a concern with the recent evidence that metals can affect the ability of fishes to mount the HVR. As Rare Earth Elements (REEs), such as neodymium (Nd), increase in demand with the shift to a low-carbon, green economy, there is a critical need to understand their environmental consequences. Here, we investigate whether exposure to Nd will blunt the HVR in fathead minnows (Pimephales promelas). Fathead minnows were exposed to 93 ± 7.9 µg/L Nd for 48-h and subjected to 40% dissolved oxygen for 1-h. The number of opercular movements were counted as a proxy of the HVR, and total Nd accumulation at the gill was characterized. Nd caused a 31% decrease in opercular breaths, and Nd accumulation in the gills was below the detection limit (LOD: 0.07 µg/L). This data demonstrates that exposure to Nd shows an effect on a fathead minnows’ ability to regulate oxygen, seen through the blunt in the HVR, potentially influencing their survivability.