The impact of simulated capture stress on elasmobranch cardiac function using isolated myocardial strips
High levels of plasma potassium (i.e., hyperkalemia) and acidosis following capture are associated with post-release mortality in fishes, although this relationship has yet to be tested or quantitatively evaluated in elasmobranch fishes. Here, isolated cardiac strip performance was measured under hyperkalemic (7.4 mM K+), acidotic (a pH decline of 0.26 units), hypoxic, and acute temperature (+/- 5° C) challenges to mimic the serological shifts occurring during a capture event. The ability of a b-adrenergic agonist (isoproterenol, 9 mM) to ameliorate any negative effects was also assessed. Cardiac strips were harvested from three phylogenetically disparate (but sympatric) species from the coastal Mid-Atlantic: clearnose skate (Rostraja eglanteria), smooth dogfish (Mustelus canis), and sandbar shark (Carcharhinus plumbeus). All data were analyzed using
generalized linear mixed models with Tukey’s post-hoc tests for significance. We found a significant negative impact of hyperkalemia on sandbar sharks that was exacerbated by acidosis and hypoxia. Clearnose skates and smooth dogfish also exhibited some hyperkalemia sensitivity, particularly with increases in stimulation frequency. In all cases, b-adrenergic stimulation improved cardiac strip performance. Our data demonstrate hyperkalemia has a detrimental impact on cardiac function in elasmobranchs, although inter-species variation is high and the magnitude of impairment low. Our results also imply future work attempting to use at-vessel blood chemistry measurements to predict post-release mortality should consider the ability of individual species to invoke an adrenaline response before assuming hyperkalemia alone is indicative of mortality.