Gas Bubble Disease
Introduction
Gas bubble disease is a surprisingly common condition in fish like Anthias and squirrel fish (Figure 1), although it can affect many different species. It is particularly common in newly imported animals and, as the common name of this disease suggests, the major symptom is large external gas-filled bubbles, which are easily visible to the naked eye. True gas bubble disease is a non-infectious condition and it cannot be transmitted between fish, although complications can occur if the wounds become secondarily infected with bacteria.
Figure 1 - Squirrel fish with severe pressure induced gas bubble disease affecting the eye. Note the pockets of gas actually in the eye (Photo ©Prof Ian Bricknell used with permission)
Figure 1 - Squirrel fish with severe pressure induced gas bubble disease affecting the eye. Note the pockets of gas actually in the eye (Photo ©Prof Ian Bricknell used with permission)
Diagnosis and Symptoms
Figures 1 and 2 both show the classic signs of gas bubble disease - large external gas filled bubbles easily visible to the naked eye. Often these bubbles are located in the eye and fin margins and may be so large that small fish may lose their balance and float uncontrollably in the water due to the large amount of gas contained within the bubbles. This is not usually a fatal condition, but eyes and fins be damaged quite severely and the bubbles can also form in internal organs, such as the liver, heart and brain, if the bubbles form in a vital area such as the atrium of the heart then death can occur very suddenly.
Figure 2 - Sea Horse with severe supersaturation induced gas bubble disease affecting the eye. Note the pockets of gas causing the layers of skin to bubble up from the underlying tissues. In this case the bubbles stopped the fish feeding. There are also smaller bubbles in the eye. (Photo ©Prof Ian Bricknell used with permission)
This disease is very hard to confuse with anything else as its symptoms are quite unique. The only similar conditions are some bacterial infections where large amount of gas can be produced in an abscess or localised area, causing the skin to bubble up with the gas released during the fermentation of the tissues. However, these bubbles caused by infection often contain pus and are usually red and inflamed whilst gas bubble disease tends to appear as “normal tissue” filled up with gas. In infectious cases the fish often appear unwell, but most fish affected by gas bubble disease appear well - avoiding nets and continuing to feed. Also, fish that have developed bubbles as part of an infection often have a rank small of decay about them when caught.
Figure 2 - Sea Horse with severe supersaturation induced gas bubble disease affecting the eye. Note the pockets of gas causing the layers of skin to bubble up from the underlying tissues. In this case the bubbles stopped the fish feeding. There are also smaller bubbles in the eye. (Photo ©Prof Ian Bricknell used with permission)
This disease is very hard to confuse with anything else as its symptoms are quite unique. The only similar conditions are some bacterial infections where large amount of gas can be produced in an abscess or localised area, causing the skin to bubble up with the gas released during the fermentation of the tissues. However, these bubbles caused by infection often contain pus and are usually red and inflamed whilst gas bubble disease tends to appear as “normal tissue” filled up with gas. In infectious cases the fish often appear unwell, but most fish affected by gas bubble disease appear well - avoiding nets and continuing to feed. Also, fish that have developed bubbles as part of an infection often have a rank small of decay about them when caught.
Causes and Treatment
There are two causes of this disease:
Cold water can hold more dissolved than warm water For example water at 10oC will hold about 11mg/l of dissolved oxygen while at 20oC it will only hold around 7mg/l (Figure 3). However, when cool water, holding more oxygen, is warmed up it does not release the extra oxygen straight away. Normally it needs to be de-gassed, allowing it to release the excess to the atmosphere prior to it being used in the aquarium. This can be demonstrated quite easily by taking some tap water and half filing a 2 litre plastic bottle and placing it in the fridge. When the water is cool shake it well, to aerate it, and place it in a warm room. As it warms up you will see small bubbles form on the side as the excess oxygen comes out of solution. If supersaturated water is not de-gassed before it is returned to the aquarium fish will take in more oxygen than their physiology is adapted for (at that temperature) and the excess will come out initially as small bubbles in the tissues before migrating to the skin and eyes causing the classical symptoms in the fish as seen in Figures 1 & 2. Again if the bubbles form in the heart or brain, as said earlier, sudden death can occur.
Figure 3 - Graph of the solubility of oxygen as a function of the temperature of the water
The situation explained above can occur quite easily in reef aquaria especially if a skimmer and chiller are used in a sump with heating occurring in the tank or in a separate compartment of the system. In this scenario the water leaves the chiller cooled and enters the sump where it can enter the skimmer and become saturated with oxygen. It then leaves the skimmer and is heated to the tanks’ working temperature and re-enters the aquarium without having a chance to de-gas. This exposes the fish to oxygen supersaturated water which will go on to allow gas bubble disease to form. The sea horse in Figure 2 came from just such a system where the cooled water from the chiller was aerated prior to it being heated and returned to the display tank without being degassed.
Treatment
Under no circumstances should the bubbles be popped as this will cause more pain for the animal and will almost certainly compound the damage as well as opening up the lesion to infection. The only way to prevent this occurring is to remove the fish from the system and place it in water with the appropriate oxygen saturation level for the temperature and fix the issue in the sump to either permit de-gassing before the water enters the display tank or heat the water to the working temperature before it enters the skimmer and becomes oxygenated.
The biggest problem is the physical disruption of tissues as the bubbles form. Often the eyes are affected (Figure 1) and the biggest problem here is blindness, as the retina can be displaced or the lens irreversibly damaged. Fins usually re-grow with no long term affect as do any displaced scales. If the bubbles form in the heart or brain, as said earlier, sudden death can occur.
2. Pressure induced gas bubble disease
This is by far the most common cause of gas bubble disease in Anthius, squirrel fish and other fish that prefer deeper reef habitats. If you imagine fish that live in deep water as a bottle of fizzy lemonade, when the cap is on the bottle the dissolved gas is kept in solution, but if the cap is released suddenly the gas is released from solution and a spectacular froth forms very rapidly. This is exactly what happens if a deep water fish is bought to the surface too quickly without adequate depressurisation (in exactly the same way as a diver needs to be depressurised to avoid the bends, or Caisson Disease as it is more correctly known). Initially the bubbles form in the tissues before migrating to the skin and eyes where they form the classical bubbles that are diagnostic of this disease. This process can take a week or two so it is quite possible that a fish is shipped asymptomatically only to develop the bubble when it arrives at its final destination. There is a school of though that also suggests that air freighting deep water fish in an oxygen atmosphere can exacerbate this condition as the fish often experience lower pressure than normal and the water is supersaturated with oxygen when compared with their natural habitat. This would explain why some fish only develop symptoms after shipping.
Treatment
Under no circumstances should the bubbles be popped as this will cause more pain for the animal and will almost certainly compound the damage as well as opening up the lesion to infection. The only way to alleviate the symptoms is to re-pressurise the fish in deep water (or as deep as the aquarium permits) if possible. Certainly I am aware of one major importer that will put any affected fish in a small pen at the bottom of their sump in about 5m of water to reduce the severity of the symptoms.
- Supersaturation of the oxygen levels in an aquarium system
- Pressure induced gas bubble disease
Cold water can hold more dissolved than warm water For example water at 10oC will hold about 11mg/l of dissolved oxygen while at 20oC it will only hold around 7mg/l (Figure 3). However, when cool water, holding more oxygen, is warmed up it does not release the extra oxygen straight away. Normally it needs to be de-gassed, allowing it to release the excess to the atmosphere prior to it being used in the aquarium. This can be demonstrated quite easily by taking some tap water and half filing a 2 litre plastic bottle and placing it in the fridge. When the water is cool shake it well, to aerate it, and place it in a warm room. As it warms up you will see small bubbles form on the side as the excess oxygen comes out of solution. If supersaturated water is not de-gassed before it is returned to the aquarium fish will take in more oxygen than their physiology is adapted for (at that temperature) and the excess will come out initially as small bubbles in the tissues before migrating to the skin and eyes causing the classical symptoms in the fish as seen in Figures 1 & 2. Again if the bubbles form in the heart or brain, as said earlier, sudden death can occur.
Figure 3 - Graph of the solubility of oxygen as a function of the temperature of the water
The situation explained above can occur quite easily in reef aquaria especially if a skimmer and chiller are used in a sump with heating occurring in the tank or in a separate compartment of the system. In this scenario the water leaves the chiller cooled and enters the sump where it can enter the skimmer and become saturated with oxygen. It then leaves the skimmer and is heated to the tanks’ working temperature and re-enters the aquarium without having a chance to de-gas. This exposes the fish to oxygen supersaturated water which will go on to allow gas bubble disease to form. The sea horse in Figure 2 came from just such a system where the cooled water from the chiller was aerated prior to it being heated and returned to the display tank without being degassed.
Treatment
Under no circumstances should the bubbles be popped as this will cause more pain for the animal and will almost certainly compound the damage as well as opening up the lesion to infection. The only way to prevent this occurring is to remove the fish from the system and place it in water with the appropriate oxygen saturation level for the temperature and fix the issue in the sump to either permit de-gassing before the water enters the display tank or heat the water to the working temperature before it enters the skimmer and becomes oxygenated.
The biggest problem is the physical disruption of tissues as the bubbles form. Often the eyes are affected (Figure 1) and the biggest problem here is blindness, as the retina can be displaced or the lens irreversibly damaged. Fins usually re-grow with no long term affect as do any displaced scales. If the bubbles form in the heart or brain, as said earlier, sudden death can occur.
2. Pressure induced gas bubble disease
This is by far the most common cause of gas bubble disease in Anthius, squirrel fish and other fish that prefer deeper reef habitats. If you imagine fish that live in deep water as a bottle of fizzy lemonade, when the cap is on the bottle the dissolved gas is kept in solution, but if the cap is released suddenly the gas is released from solution and a spectacular froth forms very rapidly. This is exactly what happens if a deep water fish is bought to the surface too quickly without adequate depressurisation (in exactly the same way as a diver needs to be depressurised to avoid the bends, or Caisson Disease as it is more correctly known). Initially the bubbles form in the tissues before migrating to the skin and eyes where they form the classical bubbles that are diagnostic of this disease. This process can take a week or two so it is quite possible that a fish is shipped asymptomatically only to develop the bubble when it arrives at its final destination. There is a school of though that also suggests that air freighting deep water fish in an oxygen atmosphere can exacerbate this condition as the fish often experience lower pressure than normal and the water is supersaturated with oxygen when compared with their natural habitat. This would explain why some fish only develop symptoms after shipping.
Treatment
Under no circumstances should the bubbles be popped as this will cause more pain for the animal and will almost certainly compound the damage as well as opening up the lesion to infection. The only way to alleviate the symptoms is to re-pressurise the fish in deep water (or as deep as the aquarium permits) if possible. Certainly I am aware of one major importer that will put any affected fish in a small pen at the bottom of their sump in about 5m of water to reduce the severity of the symptoms.
Conclusion
Gas bubble disease is a non-infectious problem caused by environmental problems either during capture and shipping or in aquarium design. Although the disease often looks disastrous for the affected animal, in many cases the bubbles resolve with few problems for the affected fish. The most common adverse outcomes are loss of an eye, bacterial infections of the lesions or brain damage. However, it is treatable and can be well managed in reef systems.