The post-release behaviour and fate of tournament-caught smallmouth bass after ‘fizzing’ to alleviate distended swim bladders

Abstract In recreational fishing, barotrauma occurs when fish that are angled from deep water are rapidly brought to the surface, causing a number of injuries and physiological alterations associated with gas expansion (such as distended swim bladders) that may impede swimming and prevent the fish from returning to depth. By deflating the swim bladder using a hypodermic needle (a process called “fizzing”) fish typically can return to depth. However, little is known about its consequences and efficacy on wild fish. At a competitive smallmouth bass ( Micropterus dolomieu ) angling event on Rainy Lake in northwestern Ontario, we evaluated the effects of post-weigh in fizzing on the behaviour and short-term survival of three treatment groups after release: (i) barotrauma fish without fizzing ( N  = 8); (ii) barotrauma fish that were fizzed ( N  = 9); (iii) fish without signs of barotrauma that were fizzed ( N  = 10) (sham control). Small external radio transmitters were affixed to the fish and tracked for 4 days. Fish were released at a common site and we assessed their dispersion at specific distances from the release site (50, 250, and 2000 m). All fish survived the 4-day monitoring period. No differences were observed in the time it took each group to disperse from the release site. Furthermore, there was no statistical evidence that fizzing influenced mean daily movements relative to controls, though a consistent trend was noted where fish that were fizzed displayed greater movement than non-fizzed fish with distended swim bladders. This study revealed that fizzing by trained experts is not detrimental to barotrauma fish. However, if done improperly there is risk to vital organs suggesting that there is merit in exploring other less invasive approaches to recompressing fish. Because our statistical power was generally low, further research is needed to determine whether fizzing should be encouraged or dissuaded to maintain the welfare status of the fish, decrease sublethal impairments, and reduce mortality.