Hypoxia tolerance is unrelated to swimming metabolism of wild, juvenile striped bass (Morone saxatilis)

Abstract

Juvenile striped bass reside in the Chesapeake Bay where they are likely to encounter hypoxia that could affect their metabolism and performance. The ecological success of this economically valuable species may depend on their ability to tolerate hypoxia and perform fitness-dependent activities in hypoxic waters. We tested whether there is a link between hypoxia tolerance (HT) and oxygen consumption rate (ṀO2) of juvenile striped bass measured while swimming in normoxic and hypoxic water, and to identify the interindividual variation and repeatability of these measurements. Fish (N=18) had their HT (loss of equilibrium) measured twice collectively, 11 weeks apart, between which each fish had their ṀO2 measured individually while swimming in low flow (10.2 cm s−1) and high flow (∼ 67% Ucrit) under normoxia and hypoxia. Both HT and ṀO2 varied substantially among individuals. HT increased across 11 weeks while the rank order of individual HT was significantly repeatable. Similarly, ṀO2 increased in fish swimming at high flow in a repeatable fashion, but only within a given level of oxygenation. ṀO2 was significantly lower when fish were swimming against high flow under hypoxia. There were no clear relationships between HT and a fish's ṀO2 while swimming under any conditions. Only the magnitude of increase in HT over 11 weeks and an individual's ṀO2 under low flow were correlated. The results suggest that responses to the interacting stressors of hypoxia and exercise vary among individuals, and that HT and change in HT are not simple functions of aerobic metabolic rate.