Bursting at the surface

Authors: Gravel, M and Cooke, S
Journal: North American Journal of Fisheries Management 28:607–617
Year: 2008
Where: Carleton University, Ottawa, Canada

Barotrauma is the injury caused when fish at depth are quickly brought to the surface by anglers.

This research, in Canada, recorded horrendous suffering to fish in a lake in Ontario during a fishing tournament:

  • three quarters of fish had signs of barotrauma - haemorrhaging or their swim bladder distended.
  • a third of fish had severe signs of barotrauma, including extreme bloating. A fifth of them later died. Fish with severe barotrauma were only slowly able to swim from the anglers when released. Some of them floundered on the surface, or were on the point of death.
  • fish floated upside down, with their gills still moving
Fish that were unable to escape to their own natural depth faced further problems:

  • predators
  • heat from the sun
  • swept by waters to inhospitable habits
  • struck by boats

"Barotrauma results from a process called decompression, where fish are brought from depth to the surface quickly, leading to rapid changes in ambient pressure."


smallmouth bass full cruelty "The decline in ambient pressure can have profound physiological and physical consequences... Beyond problems with swim bladder distention (which, in some species, includes stomach or anal eversion or swim bladder bursting), ... internal (peritoneum, kidneys, dorsal aorta)... and external (fins, gums, body surface) hemorrhaging; ocular pressure; formation of gas bubbles within the circulatory system, gills, heart, and brain... and general tissue damage"

"At a fall competitive angling event on Rainy Lake in northwestern Ontario, we evaluated the incidence of barotrauma among tournament-caught smallmouth bass."


"Overall, 76% of fish had at least one sign of barotrauma (either hemorrhaging or swim bladder distention)"

"32% of fish had two or more indicators and were thus deemed to have severe barotrauma."

"Of our examined fish, 64% showed signs of hemorrhaging and 42% showed signs of extreme bloating."


"When telemetered fish were released at a common site, we determined that fish with negligible signs of barotrauma evacuated the release site more rapidly than fish with severe barotrauma did."

"Some fish with barotrauma floundered at the surface when released, and one of these fish was subsequently hit and killed by a boat."

"At the end of the monitoring period, 20% of fish with severe barotrauma had died; two additional individuals (20%) that were still at the release site were moribund"

"Stress indices were higher in fish with barotrauma and tended to be highest among fish with barotrauma that died after release.

"Outside of a laboratory environment, a significant proportion of fish with severe barotrauma may die after release."

"When released, fish that are unable to return to depth immediately because of the added buoyancy could face predation; ... solar radiation or thermal stress; involuntary transport to shore or undesirable habitats via waves, currents, tides, or wind; injury from impact with boats; or additional physiological disturbances as they struggle to return to depth."

"All fish with extreme bloating also had problems maintaining equilibrium and were floating on the water surface during observations. In addition, when placed in the live release boats, many of these same fish floated upside down but continued to ventilate their gills."
Fish Pain