Effects of Deflating the Expanded Swim Bladder on Survival of Burbot

Abstract

We found no evidence that deflating the expanded swim bladder of burbot Lota lota affected survival. In a mark–recapture study of the species in Green Bay, Lake Michigan, many burbot caught from depths greater than 10 m floated at the surface when tagged and released because of expanded swim bladders. We deflated the swim bladders by forcing a hollow needle through the body wall to puncture the expanded organ, and we conducted two experiments to assess the effect of our procedures on survival. In one experiment 103 burbot were tagged and deflated and then held in nets on the bottom; 99% were alive after 1–8 d (mean, 4 d). In another experiment 316 burbot were tagged, deflated, and released at the surface, and 337 control burbot were tagged, not deflated, but forced to the bottom and released in a weighted net with an open bottom. Most of these fish that were recaptured were at large more than 5 months, and returns did not differ between the two groups; 6.3% of the deflated fish were recaptured compared to 5.9% of the controls. Recaptures of tagged and deflated burbot that were not part of these experiments indicated that swim bladder healing began within the first week of release and was complete in 8 weeks.