At Veterinary Vision Center, we have the special privilege of treating not only dogs and cats, but also large animals, exotic pets, wildlife, and zoo and aquarium residents. We believe all animals deserve quality veterinary care to preserve vision, and keep them comfortable when they develop ocular conditions. While most animal eyes function similarly, each species has unique characteristics that predispose them to particular diseases. In honor of National Zoo and Aquarium Month this June, we’re addressing one such disease—gas bubble disease (GBD) in fish. We explain why this phenomenon occurs, how the eye is affected, and how you can address this problem in your home aquarium fish.
What is gas bubble disease in fish?
Gas bubble disease (GBD), which is seen in captive and wild fish, causes gas bubbles to form in small blood vessels and accumulate most visibly in the fins, gills, and eyes, and sometimes the major organs. Tiny microbubbles can coalesce into larger bubbles, which block blood flow and cause tissue damage. When bubbles affect internal organs, some fish may die—sometimes without obvious outward signs—while other fish may be chronically affected, and have a reduced appetite, reduced activity, buoyancy problems, and usually some visible bubbles.
What causes gas bubble disease in fish?
The typical GBD cause is gas supersaturation (i.e., when the gasses, including nitrogen and oxygen, dissolved in tank water exceed the water’s capacity, which varies depending on temperature and atmospheric pressure). The fish absorb the excess gas, which forms bubbles in the small blood vessels, likely because of pressure changes inside their body. Supersaturation can be caused by sudden temperature or pressure changes, faulty filter equipment, or gas influx from an outside source. In wild fish, sudden gas saturation changes can occur after large algal bloom events.
What are the ocular effects of gas bubble disease in fish?
The eye is especially prone to bubble formation, because of the choroid rete mirabile (i.e., the blood vessel network that nourishes the eye). Bubbles may form behind or inside the eye, damaging the delicate structures responsible for vision. The hallmark signs include:
- Eye bulging (i.e., exophthalmos)
- Eye inflammation (i.e., uveitis, panophthalmitis)
- Bleeding inside the eye
- Cataract formation
- Visible bubbles in the front of the eye
When GBD affects a fish’s eye, the ultimate result is typically a phthisical (i.e., “dead”) eye, or complete eye loss.
How is gas bubble disease diagnosed in fish?
Diagnosis is typically made when visible bubbles are noted on physical examination. If diseased fish do not have obvious external signs, a gill tissue biopsy can confirm that microscopic bubbles are present. Water samples tested for gas saturation can also help confirm a diagnosis, but gas saturation can change over time, so normal water samples don’t rule out the disease.
How is gas bubble disease in fish treated?
To treat GBD, the source of the excess gasses must be identified and removed, because bubbles trapped inside the fish may or may not resolve when gas saturation normalizes. Some veterinarians choose to lance select bubbles, although antibiotics are needed after this procedure to prevent infection. Exophthalmos may be treated with an injection of medication around the eye, but complications could include swim bladder and buoyancy issues, so this technique is not routinely used. Once gas bubbles affect the eye and blindness ensues, simple monitoring, or eye removal, are possible treatment courses.
How can I prevent gas bubble disease in my fish?
Sometimes supersaturation events are out of your control, but the following steps can minimize GBD risk:
- Avoiding rapid temperature changes
- Regularly inspecting pumps and filters for leaks—a small leak can cause microbubbles in the tank
- Allowing water to spray from above to release trapped gasses into the air when adding water to a pond or large tank, rather than submerging a hose into the water
Keeping fish can be an enjoyable hobby, but like other pets, fish can develop eye problems that may need veterinary treatment. If you have concerns about any of your pets’ eyes, including your aquarium or pond fish, call us to schedule a visit with your Veterinary Vision Center team.
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