Barotrauma is a condition that affects fish brought to the surface too quickly. The fish’s swim bladder controls its buoyancy and is inflated and deflated by gas from the blood. However, when an angler brings a fish to the surface too quickly, this gas can’t be reabsorbed fast enough and the swim bladder expands way past its normal limits. The consequence of this is that the fish’s internal organs are crushed, causing the eyes to pop from their sockets and extending the swim bladder out of the fish’s mouth.
This can be life-threatening for the fish, but not always. Studies have shown that these effects will fade and the fish’s organs will return to their normal state when returned back to the depths. Generally, if a released fish can get to deeper water it will survive.
Releasing a barotrauma-affected fish back into the upper layers of the water column will rarely see it survive. Hampered by its inflated swim bladder, the fish can’t dive. Instead, it will float off across the surface to die a slow death or be picked off by birds or other predators.
Reef fish species, especially cods, gropers, groupers and sweetlip, are particularly susceptible to barotrauma, even from water as shallow as 15m. We get many of these species locally on our reefs and rubble grounds, however threadfin salmon is the species that is more commonly encountered and known to suffer these effects. Threadfin are a common catch in the Brisbane River and many other systems. I have witnessed bloated threadfin drifting down the river several times, even though the angler had the best intention to release the fish in a healthy state.
We all want our released fish to survive, to protect the health of the fishery, and there are several ways to do this. Numerous devices (some quite elaborate) have been used to drag fish back into the depths and then release them. Surprisingly, it is rare to find a release device for sale in a tackle store, as there are very few commercially-made release weights on the market [the only one I know of is made by Sunset Sinker Supplies in WA – Ed]. Therefore, most angler’s fashion their own crude, yet effective, deep-release devices made from all manner of materials.
Some anglers use spring-loaded lip-grip devices. One of the simplest release tools is a large hook attached upside down to a weight. However, most large, wide gape hooks are made from fairly thick steel; as this needs to go through the lower jaw of the fish, I prefer to use something of thinner diameter to minimise the impact on the fish. Some years ago I made a simple release device for my own purpose. After seeing Wayne Kampe’s segment on releasing threadfin in the last issue of the magazine, I have decided to share my version of a release weight with you. This was made from some bits I had lying around the shed, but the materials will be easy to source from any half decent tackle outlet if you don’t have them at hand. Hopefully you will want to make one to allow you to release more barotrauma-affected fish safely back into the depths.Reads: 390