Fishermen, especially bass fishermen, normally practice catch and release. The tournament anglers are very critical of bass tournaments that allow bass to die during the weigh-ins. Most of the tournaments have a weight penalty for a dead fish. The reason fish die during a weigh-in is usually due to a lack of oxygen from being kept out of the water too long or from being in a livewell too long with no aeration. In other words, the pump in the livewell is not kept on long enough to supply oxygen. Studies have shown that a bass can live approximately 4 minutes out of the water. This is about the same for humans who have no oxygen. In other words, a human can stay underwater for about four minutes before losing consciousness.
Our lungs supply oxygen to our blood system. When we breathe in air, the air goes to the lungs which transfers the oxygen to our blood and carries it throughout the body. Fish don’t have lungs and get their oxygen from the water. It’s call dissolved oxygen or DO. DO are small molecules of air that get in the water through wind and water movement. The circulation of blood in fish is different than in humans. Their heart has only two chambers in contrast to ours which has four. Their blood is pumped only in one direction. The blood enters the heart through a vein and exits through another vein and on to the gills. The gills are similar to our lungs. The gills pick up oxygen from the DO in the water and transfers it to the blood stream in the gills. The oxygen is then transported throughout the blood stream and returns to the heart. It is a closed-circulatory system.
The gills are made up of a gill arch, which gives the gill rigid support, gill filaments and secondary lamellae, which is where the oxygen transfer to the blood takes place. The blood flows through the gill filaments in the opposite direction from the water that is passing through the gills. Any damage to the gills, such as a hook penetration, can result in the fish dying.
When a fish is removed from the water, they suffocate because they cannot breathe the oxygen from the air. A fish must pass new water over their gills continuously to keep oxygenated water supplying the blood stream. A fish can also die from a lack of oxygen in the water. This has happened several times at Clear Lake during tournaments. I have taken DO readings in the affected areas and the DO meter have shown less than 1. A bass requires at least a DO reading of 3 or more to survive and the comfort zone is 5. When the DO reading drops to 1 or less there is nearly a 100 percent die-off of the bass.
The DO level is higher during the day when the aquatic plants are blooming and creating oxygen. At night the plants use up the oxygen which drops the DO level. Low DO levels can also result from dying vegetation. This is why the weed spraying companies are required to take temperature and DO level readings in the area they plan on spraying before applying the herbicides.
In many cases when the DO level drops, the fish will swim out to deeper water, but not always. Sometimes they stay in the area and die. DO levels can vary widely in the same small body of water. Often, the DO levels will be very low near the bottom and high on the surface.
In addition, bass will often die during a tournament due to rough handling by the fisherman. This causes stress to the fish and results in the fish using up the oxygen in its body.
Like all living things, a fish is a complex creature and understanding how they live and die can be a challenge.
