Effectiveness of livewell additives on largemouth bass survival

Livewell conditions during competitive angling events are thought to affect fish mortality. We examined the effects of livewell additives on initial and delayed mortality of largemouth bass Micropterus salmoides. We applied three treatments (salt, ice, or salt and ice) to livewells during tournaments conducted on lakes in Illinois, United States, as well as in laboratory and pond experiments designed to examine the effects of fish size and ambient water temperature on mortality. Fish were collected after tournament weigh-in procedures were completed and monitored for delayed mortality every 24 h for 5 d. Initial mortality did not differ among livewell additives during these field experiments. Although delayed mortality was high (35%), it was not significantly different among livewells that contained salt (56%), ice (48%), ice and salt (40%), and controls (30%). Additives administered during the laboratory experiments, at cool water temperatures, resulted in significantly lower delayed mortalities than those observed during the field experiments when ambient water temperatures were warmer. Initial and delayed mortality did not differ among livewell additives during the laboratory experiments. Larger fish in field experiments had significantly greater delayed mortality than smaller fish in the pond experiments even though initial and delayed mortality did not differ among livewell additives. Our results suggest that fish size and ambient water temperature have a greater influence on delayed mortality observed during competitive angling events than the specific livewell additives studied here.