Published July 09, 2010, 10:34 AM

Anglers should be aware of barotrauma in fish

Anglers fishing in deeper waters may have been surprised at the appearance of their catch recently. The Minnesota Department of Natural Resources (DNR) warns anglers of barotrauma, or gas bladder distension in game fish. The native game fish of Minnesota have an organ referred to as the swim or gas bladder. Gases are transferred into or out of the gas bladder through the circulatory system to maintain buoyancy as the barometric pressures change with the water depth.

By: Heather Huwe, Intern Reporter, Northland Outdoors

Anglers fishing in deeper waters may have been surprised at the appearance of their catch recently.

The Minnesota Department of Natural Resources (DNR) warns anglers of barotrauma, or gas bladder distension in game fish.

The native game fish of Minnesota have an organ referred to as the swim or gas bladder. Gases are transferred into or out of the gas bladder through the circulatory system to maintain buoyancy as the barometric pressures change with the water depth.

Barotrauma occurs when fish are reeled in rapidly to the surface from a water depth of 30 feet or greater.

The sudden change in barometric pressure causes an unnatural expansion of the swim bladder, resulting in visible physical stress.

The signs of barotrauma includes bulging eyes and portions of the stomach or intestines forced out of the mouth or anus by the enlarged swim bladder.

If the fish is released, the large volume of gas can inhibit from descending to its preferred depth. This makes the fish more vulnerable to predation, especially by fish-eating birds.

Barotrauma and associated fish mortality is increasingly being recognized as a serious conservation and fisheries management issue.

This is a particularly large issue in catch and release fisheries or deep lakes where there are special harvest regulations.

Dean Beck, from the DNR, encourages anglers to take certain measures to prevent barotrauma occurrences.

He suggests fishing in shallower waters of 30 feet or less. Also, if fishing in deeper water, anglers should try to minimize mortality by observing the size of fish that are being caught in that area.

Beck said that fish often form schools based on size. If smaller fish are being caught, the rest of the school is probably about the same size. Barotrauma can occur more easily to smaller fish so monitoring size can help reduce the number of cases.

Some anglers will try to release the pressure by inserting a needle with a syringe into the fish’s gas bladder. This is not the best measure since the fish is still being injured, said Beck.

Barotrauma can occur in all modern fish and typically all popular game fish, added Beck.

Lake Osakis has special regulations to reduce the number of barotrauma fish mortalities. There was a large number of cases due to the four-mile-hole, a 65-foot deep hole in Lake Osakis that caused many barotrauma mortalities. There is now a 15-inch minimum for walleye on this lake, said Beck.

Anglers are encouraged to exercise restraint and consider the impact they may have on the fishery or lake. Beck added that the best way to reduce the amount of mortalities is to move to a different area of the lake if the angler notices there could be cases in a certain deeper area.

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