Several names have been given to this condition in fish----fish bends, depressurization illness, etc. In the scientific realm, its most commonly called Barotrauma. What causes barotrauma and what are symptoms of the condition? It results when fish are removed from the high-depth, high-pressure zone to the surface which causes the volume of air within a fish to increase, thereby affecting fish buoyancy. Barotrauma is to fish what the bends are to human divers. External symptoms include swollen belly due to an over-inflated air bladder, floating upside down, inability to resubmerge. In more severe cases symptoms include bulging eyes, everted stomach, Barotrauma can be fatal to both marine and freshwater species that inhabit deeper depths including black basses.
What is the function of a fish’s air bladder? Its very important in that helps fish compensate for pressure- depth relationship in water. Ambient pressure doubles for every 33 feet of water depth. The air bladder allows for fish to achieve neutral buoyancy at any water depth. Neutral buoyancy is a very important mechanism in that it allows fish to conserve energy and rest more air is required in the air bladder at deep depths to achieve neutral buoyancy less air is needed in the air bladder at a shallow depth to achieve neutral buoyancy In advanced species like black basses, air is exchanged in and out of the air bladder via the circulatory system. This exchange is accomplished by the rete mirebele, the front area of the air bladder which contains a high density of blood vessels. The rate at which fish can transfer air to and from the air bladder is very, very slow. Studies of bass using hyperbaric chambers found that it takes 1 hour for a fish to fully regain neutral buoyancy after a depth change of 6 inches. Reeling a fish in slow does is not a practical way to alleviate barotrauma because of how slow a bass’s air bladder acclimates to depth changes.
. I would bet that many of you have caught fish from a depth of 10-12 feet and that fish ends up with barotrauma.
There are three common treatments used to alleviate barotrauma in tournament bass.
Specific objectives addressed by our study were: Determine the incidence, that is frequency of occurrence, of barotrauma in Amistad tournament bass and the current incidence of barotrauma treatment by Amistad tournament anglers. Determine if barotrauma affects survival of tournament-released fish. Determine and compare effectiveness of the three most popular barotrauma treatment techniques which are side-fizzing, mouth-fizzing, and deep-release. Determine if timing of treatment influences survival of affected fish, and Determine if level of training influences survival of treated fish.
The first three columns in this table are the same as presented in the table on the previous slide. The column labeled BT-neg represents percent survival of tournament fish that did not have barotrauma. The BT-pos column shows percent survival of tournament fish that did exhibit barotrauma. These Barotrauma positive fish were left untreated for the condition. For the first 3 events when water temp was 60 or less, percent survival was very high, at least 91%, for both groups of fish, those without barotrauma and those having barotrauma. At higher temps, 80 degrees and above, survival decreased considerably ranging from 43-83% for both groups of fish. For two of the 5 tournaments, BassChamps 2 and Permian SIT, barotrauma positive fish experienced statistically significant lower survival than fish not having barotrauma. These results demonstrate that barotrauma can indeed lower survival of tournament-released fish.
This table shows survival percent by type of treatment and timing of treatment, 1 hour and 5 hours after the onset of the condition. There are slight differences in percent survival between the timings for side fizz, 6%, and mouth fizz, 5%. However, statistically, these survival rates did not differ significantly between the timings. Thus, timing of treatment did not influence survival.
Next is our results concerning level of fizzer training. The percent survival values differ by no more than 6% between minimal and hands-on. For both fizzing methods, fish survival was statistically similar for minimally-trained and hands-on trained fizzers Thus, l evel of training received by fizzers was unrelated to survival of treated fish
We also evaluated if presence of blood and fish size was related to survival of barotrauma-treated fish. We found no statistically significant difference in survival of side-fizzed fish between those that bleed and those that did not. Alternatively for mouth fizzing, we found we found statistically significant lower survival of mouth fizzed fish that bled compared to those that didn’t bleed, 43 versus 89% For fish size, lengths of surviving and dead fish varied by less than 1 inch for all three treatment types. There was no statistically significant relationship between fish and survival.
Why did mouth fizzing cause lower survival? We believe it is due to trauma to the rete mirabile and close proximity of other vital organs to the mouth fizzing needle insertion location. The rete mirabile is the anterior (forward) area of the swim bladder within the green circle. It is different than the posterior portion of the swim bladder in that it contains a much higher density of blood vessels and is the location at which gas is exchanged in and out of the swim bladder. In mouth fizzing, the needle impacts this most important part of the swim bladder as shown. Also, close by the mouth fizzing insertion location are the verterbral column and the anterior kidney which is sandwiched between the vertebral column and the rete mirabile. Both of these organs are vital to a fish’s health. If mouth fizzing and your syringe fills rapidly with blood, you have hit the anterior kidney, and in our experience this is usually fatal. In looking at the overall layout of the swim bladder, side fizzing is safer because the swim bladder presents a larger target and vital organs are more distant from the needle insertion location.
I would like to acknowledge our partners and cooperators for this project. The National Park Service provided use of their dock for our study and purchased the large holding pens, and Sul Ross University provided the fish tags we used. Cooperators in our study were Bass Champs, BASS-elite Series, FLW, Texas Bass Federation, Permian Bass Club, and Angler’s Lodge. We would also like to extend our thanks to the many Inland fisheries staff that helped and participated in our study.
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