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Non Contagious Diseases

Gas Bubble Disease

The condition of gas bubble disease is very similar to the “bends” which divers experience when they rise from deep water to the surface too quickly. The rapid change in pressure results in tiny bubbles forming in the blood, body cavities, tissues and skin layers of fish. This “disease” is caused by super saturation of pond water with dissolved gases. It occurs under various conditions. The first is where cold water that is already saturated with gas, flow into a pond where it may be heated without adequate time or aeration for volatilization of excess gas. It also commonly results when water from deep wells, often high in nitrogen gas and carbon dioxide, is brought into an aquaculture facility without proper aeration. It can also be caused in small pools by leaving a garden hose running on the bottom of the tank. The water in the water reticulation system is under tremendous pressure and once the hose is submerged, there is no release of excess gas to the atmosphere, resulting in super saturation of pond water and the resultant complications. Gas bubble disease can also occur where a small leak exists before the pump inlet of a pressurised system. It has also been associated with faulty pumps and, although rare in ponds, the presence of heavy algal blooms when high levels of oxygen are released into the water during photosynthesis.

As water, which is supersaturated with nitrogen and oxygen gasses, passes over the koi’s gills, high levels of gas enter the bloodstream. Once these gasses are in the koi’s bloodstream, a change in pressure result in these gasses to come out of solution and form tiny bubbles in the blood. These bubbles are known as embolisms. Nitrogen bubbles in the blood can block blood vessels and severely affect the circulation. This may result in abnormal behaviour, erratic swimming and even death. I have witnessed stress induced reddening of the skin, especially the fins, minutes before they succumb.

External signs of gas bubble disease are small bubbles that are visible around the eyes, on the fins and on the gills. Nitrogen Bubbles may cause the eyes to swell and even pop-eye (exophthalmia) to develop. When trapped between layers of the skin, lifting will appear. Small bubbles can form within the vascular system, blocking the flow of blood and causing tissue death. Worse, bubbles can form in the gill lamellae and block blood flow, resulting in death by asphyxiation.

Treatment of gas bubble disease is to vigorously aerate the pond to volatilise the excess gas. Agitate the pond surface also as this will further assist the access gas levels to diffuse back into the air. Also replace large amounts of water with water that is not supersaturated. Make sure the new water is properly treated for chlorine.

Normally if these steps are taken, no further treatment is necessary. If however nitrogen bubbles have formed in the blood, you may expect some losses.

When a pressurised system is causing super saturation of gasses in the pond water, it is sometimes difficult to detect. A telltale sign of this occurrence is very small bubbles emerging from the return pipes into the pond. Sometimes these fine bubbles are hardly noticeable, and only form a fine froth but believe me it may have a severe impact on the water in the pond. Another sign is when fine bubbles appear on plants and all submerged surfaces. When a hand or net is dipped into the water, fine bubbles starts to form immediately.

Despite the fact that the effects, the identification and the possible treatment has been discussed, it is very important to identify the cause/origin of the problem and to rectify it. Sometimes you know it is a leak at the pump intake but cannot see or hear exactly where the problem is. Some advice I can offer is firstly, to fill a normal spray can with water and spray it on the suspected union or the pipe fitting where it joins the pump. This leaves a shiny surface over the plastic/pvc except at that pinhole size opening where air is being sucked in. A length of tubing is also excellent for listening where exactly the intake “hiss” comes from.

Do not underestimate the seriousness of gas bubble disease. I have seen a small fish swim through these micro bubbles exiting a pipe, with dire consequences!

Last Updated on Tuesday, 11 November 2008 16:09