Gas Bubble Disease

Definition:

Gas bubble disease (GBD) is a non-infectious, induced process caused by high total dissolved gas pressure, which produces primary lesions in the blood (emboli) and tissues (emphysema), and subsequent physiological dysfunction. It presents the opposite problem to hypoxia!!

Causes and pathogenesis:

Dissolved gases are typically measured in milligrams per liter. However, the level of saturation is typically presented as a percent of saturation. This is the percentage of the total gas concentration relative to "saturated" conditions.

% Saturation = C/C* x 100 (%)

where:

C = dissolved gas concentration (mg/l)

and

C* = saturation dissolved gas concentration at a given temperature, pressure, and salinity (mg/l)

Water of different temperature, salinity, and pressure holds differing amounts of gases. When the concentration of a gas, such as nitrogen, is the exact amount the water can hold for its pressure, temperature, and salinity, the water is considered "saturated". When there is more gas than the water can hold, it is "supersaturated". If there is less gas, it is "undersaturated". So, if we say that the percent of saturation is 115%, this means that the actual dissolved gas concentration is 15% greater than the saturated dissolved gas concentration at the given temperature, pressure, and salinity.

The principal gases found in the water are nitrogen, oxygen, and carbon dioxide. The super (over) -saturated liquid will constantly attempt to release the excess gas in the form of small bubbles, as the access gases will come out of solution. Similarly, when a fish is exposed to a supersaturated environment, the gas dissolved in the tissues and fluids is forced to come out of solution and if this happen too rapidly, bubbles form in different parts of the fish, causing a variety of signs and symptoms.

Nitrogen is the most common of the inert gases in fresh and salt water, and enters a fish through its gills, just like oxygen. It is then carried to the tissue by the blood. Once distributed, nitrogen remains in the tissue while oxygen is consumed. Because fish do not metabolize nitrogen, it is the gas most commonly associated with gas bubble disease. Oxygen moderately above saturation in water is not typically a problem because fish use oxygen to breathe. Nonetheless, oxygen supersaturation due to phytoplankton blooms, coupled with late afternoon pond warming, is quite common.

1. Pressure can increase the amount of gas per unit volume that water contains. One of the best practical demonstrations of this law is offered by opening a bottle of carbonated beverage. When the cap is removed from the bottle, gas is heard escaping, and bubbles can be seen forming in the drink. This is the carbon dioxide gas coming out of solution as a result of sudden exposure to lower barometric pressure.

a. A rapidly changing barometric pressure over the path of hurricane Andrew in 1992 has induced GBD which was considered a major culprit in the death of almost 10 million marine fishes valued at $7.8 million.

b. The deeper the water, the more gas the water can hold.

c. Water that is pumped through pressurized systems will hold more gas than unpressurized systems.

2. Water at higher temperature holds less gas per unit volume because it is less dense. Thus, if the temperature of cold water with a normal dissolved gas content is raised due to increased environmental temperature, supersaturation conditions can be created.

a. Problems with GBD are commonly encountered when fish are cultured in the heated effluents of power plants or where heat is recovered from steam generating facilities.

3. The higher the salinity, the less gas water can hold. This is because the dissolved salts take up room that the gas could be using.

4. Supersaturated conditions can also result if a gas such as nitrogen is forced into solution

a. a crack in a pipeline

b. water falls

c. excessive splashing

Symptoms:

Affected fish may display acute morbidity (illness) and mortality (death). Fish eggs can tolerate a relatively high total gas pressure of 110%-115%. After the eggs hatch, however, they are very sensitive to supersaturation damage with mortalities expected at gas (nitrogen) pressures ranging from 102% to 105%. Adult fish are more tolerant of excessive total gas pressure conditions, on the order of 115%-120%. Problems can arise at 105% saturation, and at 140% saturation and higher GBD can kill fishes.

1. Gas bubbles can form in the body cavities of fish, such as behind the eyes causing exophthalmia, or between layers of skin tissue.

2. Bubbles can form in the thin tissue between the fins on and along the back and tail.

3. Small bubbles can form within the vascular system, blocking the flow of blood and causing tissue death.

4. Worse, bubbles can form in the gill lamellae and block blood flow, occasionally resulting in death by asphyxiation.

5. Blisters are clearly visible beneath the skin, particularly in the head area, in and around the eyes.

6. Sick fish will make a croaking sound when removed from the water, and the skin will crackle if you run your finger across it.

Diagnosis:

Supersaturation disease can be difficult to confirm since problems visible to the naked eye (gross lesions) are commonly not present when the fish are found. Gill biopsies and wet mount examination of other organs under the microscope may show gas emboli within the bloodstream. Supersaturation is difficult to diagnose with a water test kit since most kits do not measure dissolved nitrogen. You should consider a diagnosis of supersaturation disease for any acute deaths that cannot be attributed to other water quality disorders or specific pathogens or toxins.

Treatment:

Gas bubble disease is rarely reversible because of the damage to the internal organs. Attempts to "pop" these superficial bubbles do not get to the cause of the problem and probably do more harm than good, as it causes infection and most likely increases the suffering of the animal.

Prevention:

It is obviously better to avoid a situation than to have to cure one.

1. Avoid, if possible, causes of supersaturation.

2. Perform an immediate water change to restore the proper gas balance.

3. Clean away Algae and reduce the amount of live plants.

4. Reduce lighting to reduce oxygen production by the plants.

5. Good aeration is one of the simplest ways to prevent GBD. Bouncing, splashing, spraying, and/or cascade culture water through air before it reaches fish will promote the release of supersaturated gases.

6. Increase salinity, if possible.