You might know barotrauma by a different name, like “hyperbuoyancy” or “overinflated swim bladder.”
You might have even seen pictures of deepwater marine fish with bug eyes or their stomachs pushed out their mouths. Maybe you have witnessed it yourself.
But barotrauma is not restricted to ocean-dwelling fish.
Bass and crappie in Mississippi waters can be victims, too — especially during the winter, when anglers are more apt to fish deeper than 30 feet.
Barotrauma is not an issue if you intend to harvest the fish. But if you plan to release a fish, whether practicing voluntary catch and release or complying with a size or bag limit, fish with barotrauma are likely to die without assistance.
How the swim bladder works
Almost all fish have a swim bladder (aka gas bladder). This organ, which looks like an elongate balloon, is in the body cavity immediately below the backbone.
Often a single, air-filled sac, it can also have several compartments, as occurs in catfishes.
The swim bladder adjusts the fish’s buoyancy. Pump air in, and the fish becomes more buoyant and floats. Release air or pump air out, and the fish becomes less buoyant and sinks.
A bottom-dwelling fish benefits from being negatively buoyant, but a fish like a bass or a crappie that swims in the water column benefits from being neutrally buoyant. Neutral buoyancy allows the fish to maintain its position in the water column without needing to swim and expend energy.
Water is heavy stuff and exerts a lot of pressure on a fish as it swims deeper. The increasing pressure compresses the air in the swim bladder, and the fish becomes less buoyant. So air must be pumped into the swim bladder to maintain neutral buoyancy.
Air is pumped into the swim bladder by the gas gland (the technical term is rete mirabile, which translates to “wonderful net”). The gas gland is able to move gases from the blood into the swim bladder to inflate the cavity and make the fish more buoyant.
When a fish moves up in the water column, the pressure decreases and the air in the swim bladder expands. The gas gland can also remove air from the cavity to make the fish less buoyant, but the transfer of gas is a slow process.
Some fish, like shad and catfish, have a connection between the swim bladder and stomach that allows the fish to rapidly change depth without experiencing on overinflated swim bladder. When the fish moves up in the water column, the pressure decreases and the swim bladder expands.
This “excess” air can pass to the stomach and be released through the gut. The fish literally burps the excess gas.
But the swim bladder is a closed sac and not connected to the gut in fish like white bass and those in the sunfish family, which includes bass and crappie.
So when you hook and quickly reel a fish with a closed swim bladder to the surface, the air in the swim bladder expands. Lacking a “release valve” of a connection to the gut, the fish becomes positively buoyant (hyperbuoyant) and cannot submerge.
With a great change in depth, the swim bladder might expand to fill much of the body cavity and push the stomach out the throat and mouth.
Perscription for Barotrauma
An over-inflated swim bladder is not necessarily fatal. After several hours, the gas gland can reduce the amount of gas in the swim bladder.
However, the fish might exhaust itself trying to submerge, and the floundering fish is a target for fish-eating birds or other predators.
Diagnosing barotrauma is simple: Whether in a boat livewell or on the lake surface, the fish floats on its side and cannot submerge.
Barotrauma can be relieved two ways.
• Venting — Use a hypodermic needle or a venting tool. The needle should be inserted through the side of the fish and into the swim bladder (see picture).
The attahced video developed by Texas Parks and Wildlife Department shows a safe and effective way to vent a fish with an overinflated swim bladder. Instructions for venting begins at about the 4-minute mark.
The location for venting a crappie is roughly the same as for a bass.
• Deep-water release — Use a weighted basket to lower the fish to the depth of capture. Tie a rope to the bottom of a laundry basket and attach some weight to the rim. When you hold the basket by the rope, it is upside down.
Simply but the basket over the floating fish and lower the basket to the depth at which you caught the fish. The increased water pressure will make the fish neutrally buoyant.
Someone once suggested you can minimize barotrauma by not fishing deep. Certainly, that is a true statement but not a solution; I go fishing to catch fish, and occasionally that means fishing deep and dealing with barotrauma.
It appears that barotrauma often is not always instantaneous and a fish caught from deep water that is quickly released often can submerge.
So make your decision about whether you intend to harvest that bass or crappie before it gets to the surface. If you intend to release the fish, quickly unhook it while still in the water and immediately release it.
But if it floats after release, it is necessary to vent the fish or use a deep-release basket.