Impacts of dissolved oxygen on the behavior and physiology of bonefish: Implications for live-release angling tournaments

Saltwater tournaments for bonefish (Albula spp.) often retain fish in livewells for up to 8 h to allow fish to recover from the physiological disturbances associated with angling. During livewell confinement, oxygen concentrations may fall due to elevated biomass of fish, coupled with low exchange of water. Some anglers use oxygen infusion systems, potentially exposing fish to water that is supersaturated with oxygen. Currently, the effects of differing levels of oxygen on bonefish recovery are unknown. Because physiological disturbances related to angling can influence the probability of post-release predation in bonefish, livewell conditions that maximize recovery rates without imparting additional negative consequences need to be defined. The objective of this study was to assess the behavior, physiological response (i.e., blood chemistry), and metabolic rates of bonefish recovered in hypoxic, normoxic, or hyperoxic seawater after exercise (i.e., a simulated angling event). Behavioral experiments consisted of placing bonefish in one of three dissolved oxygen concentrations and monitoring gill ventilation rates. For blood sampling and metabolic rates, bonefish were exercised and then recovered in different dissolved oxygen concentrations, replicating an angling event coupled with different livewell holding conditions. Both hypoxic and hyperoxic conditions caused bonefish to experience behavioral and physiological disturbances, compared to fish in the normoxic treatment. In addition, bonefish used more energy when recovered in hyperoxic seawater and fish in the hypoxic treatment were unable remove lactate compared to fish in the normoxic treatment. These results indicate that anglers and tournament organizers should recover angled bonefish in normoxic seawater. To achieve these conditions, dissolved oxygen concentrations should be monitored with a commercially available meter and maintained between 4–8 mg/L by circulating fresh seawater into livewells.

Research highlights
► Bonefish are kept in livewells during live-release tournaments.
► Dissolved oxygen concentrations in livewells may be hyperoxic, hypoxic or normoxic.
► Fish experienced physiological and behavioral disturbances in hyperoxic or hypoxic water.
► Bonefish metabolic rates increased when recovered in hyperoxic water.
► Anglers should maintain dissolved oxygen concentrations at 6 mg/L.