The efficacy of assisted ventilation techniques for facilitating the recovery of fish that are exhausted from simulated angling stress

Employing science-based best angling practices is important for sustainable catch-and-release fisheries. In situations where fish lose equilibrium (unable to maintain upright posture to swim in a coordinated manner), anglers often provide assisted ventilation by hand, which typically involves maneuvering fish to move water over the gills until equilibrium is regained. However, it is unclear whether these tactics are effective at facilitating physiological and behavioural recovery and improving survival. Here we tested the efficacy of assisted ventilation techniques in two freshwater species popular for angling, largemouth bass and brook trout. Fish were captured by angling with rod and reel, and subsequently air exposed until equilibrium was lost. Treatments included maneuvering fish in a back-and-forth manner or in a constant forward motion, which were compared to controls that did not experience assisted ventilation. In largemouth bass, physiological stress values (i.e., blood glucose, lactate, pH, hematocrit) and rates of equilibrium regain were not significantly different between treatments, while all fish survived a 24-h holding period. In brook trout, fish maneuvered in a back-and-forth manner regained equilibrium fastest, but differences between treatments were not statistically significant. Further, once equilibrium was regained, brook trout often spent extended periods resting on the bottom, and likely had limited capabilities to avoid predators. We found little evidence of any physiological or behavioural benefits of two common assisted ventilation techniques that would result in improved fish survival or fitness with largemouth bass or brook trout in recreational angling scenarios. However, releasing fish in poor condition may lead to greater predation risk, so retaining fish with minimal handling until swimming capabilities return is likely the most advisable course of action.