Dealing with Bent Bass

By Jami Kanowski.

What is Barotrauma ? – Barotrauma or the bends is an issue affecting many tournament and recreational anglers in Australia. It affects many deepwater species of Australian Fish including bass and will generally only be seen in fish caught in deeper water.

Barotrauma is caused by the expansion of gases contained within the swim bladder which all fish use and regulate to achieve neutral buoyancy. As the captured fish ascends in the water column these gases expand rapidly distending the air bladder to the point that the fish can be incapable of regulating the condition itself.

It can also cause gas bubbles in the bloodstream and organs as in human barotrauma however this seems to occur most commonly in deep water reef species.

A fish with an overfilled air bladder is generally incapable of returning to the depths without assistance. It will appear hard to the touched and can look as though bloated and may have bulging eyes, vent, or the back of it’s throat may protrude from it’s mouth.

Mortality rates can be fairly high with fish dying on the surface unable to process water through their gills and becoming easy prey for predatory species. Fish will suffer from barotrauma in varying degrees, with some needing intervention while some need little or no assistance.

In Australian Bass many anglers have noted that the larger the fish the more likely it is to require intervention by the angler. And while there is limited research in relation to this issue, all scientific theories I have been able to locate agree that for the best chance of survival, action needs to be taken by the angler immediately.

There Australian Government suggests several methods of dealing with barotrauma in it’s good practice guide (found at These are:

• Do Nothing – Simply do nothing as some fish are able to equalise their pressure quickly and return to the depths.
• Weighting – Apply a weight to the fish to assist in its return to the depths where the gases in their swim bladders with quickly recompress to normal levels. This is achieved by tying a weight to a barbless hook and lowering the fish to the required depth. A cord is then tugged to free the fish. This technique is most commonly used in deep reef conditions.
• Venting – Needling or venting the swim bladder by spiking the bladder with a sharp hollow tube is the most commonly used method of relieving barotrauma in Australian Bass. This is a very effective method of releasing bass, but only when done correctly. I have observed many anglers with the best intentions, struggling to find the correct position to spike the fish and generally botching the job.

How do I vent a bass? – Observing the below diagram I have shaded the correct puncture area and the methods of finding it.

Method 1: This area as described in the good practice guide is located by drawing a line vertically down from the fourth dorsal spine and horizontally across the top of the pectoral fin.

Method 2: Lay the pectoral fin down flat and count three scales down from the lateral line in line with the tip of the fin.

Once the needle is inserted, it is best to twist it as you go deeper. This stops the needle aperture from getting blocked. Continue to insert the needle until you reach the air bladder which will release gas in a hiss through the needle. Hold the needle in until you can no longer hear the gases escaping. You will also see the fish visibly deflate. Do not try to remove all of the gases from the fish as the fish needs these gases to survive. I generally remove the needle when I can no longer hear the gas escaping.

When using Method 2 which I prefer, you should insert the needle on about a 45 degree angle towards the head. I have observed that by angling the venting needle, the fish’s musculation is able to immediately close the wound on removal of the needle. In other methods the gases will continue to escape once the needle is removed. When using this method you will notice that the bubbles will stop once the needle is removed.

If the fish is still unable to sink itself in the water it will probably need further attention. Check where you have inserted your needle. There may be a trail of bubbles leading from the puncture however this is unlikely when using Method 2. If this is so, it is best to leave the fish in the water and just observe its progress. Do not try to force the gases out by applying pressure to the sides of the fish as you will most likely cause damage to the internal organs.

There is some conjecture regarding the size needle to use with many saying that the smaller the needle the quicker the fish recovers. I have been most successful with an 18 gauge, 1 ½ inch needle. This is a fairly large bore needle but never seems to clog up and allows a quick release as it vents the fish quickly.

The fish is believed to be able to heal the puncture in its swim bladder within hours and several have been caught again within minutes of release. The wound in the fish’s side should heal in a matter of days.

If you are still unsure of inserting a needle into a fish or have moral issues with this process, I would recommend that you do not fish deep presentations because if you are not prepared to learn these techniques any fish you catch is going to die. I have spent hours going through research papers and similar and there is no other accepted method of release which will ensure the survival of the fish as well as venting the swim bladder or weighting.

While weighting would in my opinion be the preferred and less intrusive option it is simply not applicable to fish that are going to be kept alive in a livewell. By all means use it on the fish you release, but you will still need to learn how to vent the fish you keep.

There has been much attention on fish mortality rates as a result of deep fishing techniques and the mortality rates of tournament fishing. I believe that this has stemmed from no action being taken rather than needling or venting fish or the fact that the venting is not performed at capture when it is most successful.

If the angler takes the effort to learn when and how to do the procedure properly, it is no different to placing a needle like hook in the mouth of the fish to capture it in the first place.