Your angelfish is upside down because it is struggling with buoyancy. Under normal conditions, fish swim upright as they move through the water. Swim bladder disease is most likely the culprit, an umbrella term covering issues that can develop from several sources.
As freshwater angelfish keepers, we have experienced our share of fish showing a swim bladder issue. The good news is we have seen most of our prized fish recover. That is why we want to share these experiences with you; the more knowledge you have, the better keeper you will be.
Let’s take a look at some things that can help you identify, treat, and prevent your angelfish from having its world turned upside down, including:
- How freshwater angelfish swim
- The swim bladder
- Swim bladder disease
- Other reasons your angelfish is upside down in tank waters
Do Angelfish Swim Upside Down
Freshwater angelfish usually swim upright in the aquarium. You might catch them with an elevated head when swimming toward the tank surface or head down when they move toward the substrate, but they remain upright.
We have seen fish that swim erratically (including upside down) when avoiding aggressive tank mates, during mating movements, and hugging walls or plants. These tend to be quickly passing moments, however, and the fish return to swimming upright after a few seconds at most. Some fishkeepers even report individual fish swimming upside down because it appears to like it!
How does a fish swim?
A fish uses a set of muscles along its side called myomeres to push its body against the water. Its flexible spine moves back and forth, helping to propel it. The caudal fin aids this movement as it acts like a paddle pushing against the water.
Those little pectoral fins you see on the side of your angelfish help with side direction and speed. Its lower pelvic (or ventral) fins aid with up and down movements and stability. The long anal and dorsal fins that give freshwater angelfish their height also help with balance and stabilization.
Your pet angelfish (part of the Pterophyllum genus) is a cichlid. Cichlids are part of the superclass called Osteichthyes, or bony fish. One characteristic of bony fish is that they have an internal organ called the swim bladder (some keepers and older literature might call it an air bladder).
A swim bladder issue is often why your angelfish is swimming upside down.
Why Is My Angelfish Swimming Upside Down
Why is my fish upside down at the bottom of the tank?
If you notice your angelfish swimming upside down, it is having problems with buoyancy. What is buoyancy? In the fish world, your pet can displace an equal or greater volume of water than its body, allowing it to float in the water column.
Buoyancy allows your fish to maintain depth or move higher and lower in the aquarium. When this ability is compromised, it will cause issues with proper swimming. Finding your angelfish upside down in the tank is due to its inability to maintain an upright position because something interferes between body buoyancy and the surrounding water in the tank.
In our years of keeping freshwater angelfish, swim bladder disease is usually why your angelfish is upside down.
Swim bladder disease
What is a swim bladder?
Cichlids, including freshwater angelfish, have a swim bladder. It is an internal organ that inflates and deflates, filled with air. A swim bladder nestles below the spine in the upper body, allowing the fish to swim upright, even when fully expanded.
When filled, your angelfish becomes more buoyant and rises in the water column. Conversely, a deflated swim bladder creates less buoyancy and the fish sinks.
What is swim bladder disease?
This disease (also called swim bladder disorder) can be caused by inflammation or through fluids within the organ. Other issues can also exasperate this disorder by preventing the swim bladder from working.
Angelfish upside down near the bottom of the tank cannot deflate their swim bladder with enough gas to maintain an upright position but struggle with buoyancy enough to keep them at the bottom of the tank. If your angelfish is upside down in tank waters near the surface, it might have issues deflating its bladder, and that prevents it from swimming upright and forces it to the surface.
How do you treat swim bladder disease in angelfish?
One way to diagnose swim bladder disease is when you notice a sudden change in swimming.
If your pet’s fins appear to be in working order and it struggles to remain upright, that is a clue. Various conditions in the tank water, a bacterial infection, or issues from a bloated belly can be sources of the problem. While some of these issues can be hard to detect, clues like foods in the water from a lack of appetite or multiple fish getting sick with the same symptoms can help with diagnosis.
Once you feel confident that swim bladder disease is the problem, it is time to treat it.
If the tank water is off chemically, it can interrupt the nitrogen cycle. Performing a water change might be all you need to reestablish healthy water parameters. Where overfeeding is the suspected culprit (a swollen belly), you can treat the angelfish for constipation. Treatments with anti-bacterial medications can also return your freshwater angelfish to an upright swimming position.
Other reasons your angelfish is upside down
Damage to fins
Issues with the swim bladder are not the only reason you find angelfish upside down in the tank. Damaged fins or fins that are not functioning can be the problem.
While the various species of angelfish are known for their hardiness, the long fins are susceptible to damage. Physical damage can occur during fights between the fish and its tank mates, from objects in the aquarium, and mishandling during transfers. Other forms of damage can occur from things like fin rot.
Some damage can be treated or healed over time, with recovery solving swimming issues. At other times, the damage may cause permanent problems with swimming upright.
A bloated belly can occur due to constipation, where your freshwater angelfish can not excrete wastes, causing a build-up within the abdomen. As the body swells, it cramps internal organs, including the swim bladder. The bladder may not be able to expand, preventing the fish from maintaining a proper swimming position or causing it to drop to the bottom of the aquarium.
If you are overfeeding your pets, stop feeding them for a day or two to see if that helps. You can also treat them for constipation to help stimulate the clearing of the digestive system.
Infections can affect how your angelfish moves through the water. Bacteria and viruses are the cause. Fungal growths and parasites can also negatively affect buoyancy. Many of these problems are treatable, with full recovery possible.
Genetic mutations usually develop early in fry or juvenile specimens, but issues may not arise until adulthood. These tend to be untreatable in our experience, and the best you can do is adapt the tank to prevent further complications (examples include using foods that stay at your pet’s water level or a smooth substrate for fish stuck at the aquarium bottom).
General weakness and stress
External body factors can cause generalized weakness beyond the problems mentioned above and is an overlooked reason for finding an angelfish upside down in an aquarium.
A starving fish can reach the point that it struggles to maintain an upright position. Water parameters might be wrecking your pet’s immune system or metabolism. Monitoring tank water and observing your fish when you feed it can help pinpoint these potential issues.
Stress affects tropical fish, and your freshwater angelfish might be overwhelmed by its environment. The chemical composition in the water, extreme temperatures, and tank mate issues are typical stress triggers. Luckily, all of these are within your control to modify.
If you find your angelfish swimming upside down in your aquarium, it is usually due to issues with its swim bladder, like swim bladder disease.
Other issues include:
- Fin damage
- Angelfish diseases
Most problems are treatable, but some are permanent. Monitor water parameters and your angelfish to identify issues quickly. If you have any questions, don’t hesitate to ask so we can answer them.