If you’ve ever had an aquarium, you’ve likely noticed your fish swimming to the surface and releasing bubbles. This peculiar behavior may have left you wondering why fish blow bubbles and what purpose it serves. Read on as we dive into the reasons behind this aquatic activity.
If you’re short on time, here’s a quick answer to your question: Fish blow bubbles at the top of the tank as a normal part of their respiration process. The bubbles are pockets of air that get trapped on their gills or swim bladder as fish inhale oxygen at the surface.
Fish Breathe Oxygen Like Land Animals
Just like humans and other land animals, fish need oxygen to survive. However, since fish live underwater, they have evolved special organs called gills to extract oxygen from the water around them.
Gills Extract Oxygen from Water
Located on each side of a fish’s head, gills are composed of filaments filled with blood vessels. As water passes over the gills, the dissolved oxygen moves across the thin walls of the blood vessels and enters the fish’s bloodstream.
This oxygenated blood then circulates through the fish’s body, delivering the vital oxygen to its organs and tissues. Amazingly, some fish can extract over 80% of the available oxygen from water using their highly specialized gills.
The structure and number of gills differ among fish species. Sharks, for example, have five pairs of large gill slits on each side of their heads, while trout have four pairs of smaller gill covers. Regardless of these differences, gills serve the same essential purpose in all bony and cartilaginous fish.
Swim Bladder Stores Air for Buoyancy
While gills provide fish with the oxygen they need, most fish species have another specialized organ that allows them to maintain neutral buoyancy in water: the swim bladder. The swim bladder is a gas-filled sac that fish can inflate or deflate to control their depth and orientation in the water column.
Fish actively regulate the amount of gas, usually oxygen, in their swim bladders to match the density of the surrounding water. This helps counteract the weight of their bodies and internal organs. By changing the volume of gas in their swim bladders, fish can control their buoyancy and expend less energy staying at their desired depth.
Physoclistous fish like trout have closed swim bladders that don’t connect to the gut. These fish gulp air from the surface to fill their swim bladders. In contrast, physostomous fish like goldfish have open swim bladders connected to the esophagus.
They can fill their bladders by gulping air or removing gas from the bloodstream.
So in both form and function, fish have evolved specialized respiratory systems that allow them to breathe underwater. Their gills and swim bladders give fish everything they need to obtain oxygen and navigate their watery homes with grace and ease.
Bubbles Result from Surface Breathing
Inhaling Air at the Surface
When fish come up to the surface of the aquarium water, they open their mouths and inhale oxygen from the air above the water (😲). This allows them to “catch their breath” since there is more oxygen in the air than dissolved in the water.
The air contains about 20% oxygen, while water typically contains less than 10% of the oxygen found in the same volume of air. Inhaling oxygen-rich air allows fish to quickly replenish their oxygen supplies.
Air Pockets Get Trapped
As fish inhale at the surface, some of the air gets trapped in their mouths and gill chambers in the form of small air bubbles (👄). These air pockets then get carried under the water as the fish swim back down. Fish gulp air into buoyancy chambers or other cavities, and the air has to come back out.
Bubbles Released When Fish Swim Down
The trapped air bubbles are released from the fish’s mouth and gills when the pressure increases as the fish swims to lower depths. The air bubbles are less dense than water, so they immediately float up to the surface.
This is why you may notice a stream of bubbles released from a fish that has just darted to the bottom of the aquarium after gulping air at the surface.
Some fish even have special physiological adaptations to hold onto bubbles, such as anabantoids like bettas and gouramis. These labyrinth fish can breathe oxygen from the air thanks to a special suprabranchial organ that allows them to trap and process air bubbles.
The bubbles slowly release oxygen that gets absorbed into the bloodstream.
Why Fish Go to the Surface in the First Place
Seeking More Oxygen
One of the main reasons fish go to the surface is because they are seeking more oxygen. Just like humans need oxygen to breathe, fish absorb oxygen from water through their gills. However, the amount of dissolved oxygen is lower at deeper levels of the tank.
This lack of oxygen can cause fish to feel short of breath. Going to the top allows them to gulp water that is more highly oxygenated.
Some fish are more sensitive to low oxygen levels than others. Small fish with high metabolisms like tetra and guppies need more frequent access to oxygen. Bottom-dwelling fish like catfish and plecos are accustomed to lower oxygen at the substrate level.
But all aquarium fish will occasionally dash to the surface when they need an oxygen boost.
Adjusting Swim Bladder
Another reason fish head to the surface is to adjust their swim bladder. The swim bladder is an internal gas-filled organ that helps fish maintain buoyancy and balance in the water. To stay neutrally buoyant, fish need to regulate the amount of gas in this organ.
Fish add gas to their swim bladder by gulping air at the surface. This is why you might see a fish zoom to the top and appear to take a quick “breather.” Some fish like gouramis have a special respiratory organ called the labyrinth organ that allows them to breathe air directly to supplement their gills.
After catching a breath at the surface, they can dive back down.
Escaping Poor Water Conditions
Finally, fish may hang out near the water’s surface when something is off with their tank conditions. Problems like high ammonia, low oxygen, and improper pH can make them uncomfortable. Hanging out at the top is their way of trying to escape poor water quality.
You’ll often see fish gulping at the surface when parameters are off. It’s their attempt to maximize oxygen intake while avoiding the bad conditions below. Bottom-dwelling fish may even leave their usual spot on the substrate and hover higher up.
So if your fish are persistently sticking to the top level, it’s a sign to test your aquarium water. Performing partial water changes can help restore proper conditions if ammonia, nitrites, or nitrates have built up.
Checking your filter, aeration, and other equipment will help troubleshoot oxygen issues.
Bubbles Indicate a Healthy, Active Fish
Sign of Normal Respiration
Fish breathe through gills that extract oxygen from water as it passes over them. The regular release of bubbles from a fish’s mouth is a reassuring indication that its gills are functioning properly and taking in ample dissolved air (Source: https://www.thesprucepets.com/aquarium-fish-blowing-bubbles-1381230).
Most species will blow 10-30 bubbles per minute. An increase or decrease in this baseline can signal respiratory issues. However, pufferfish and bettas blow more bubbles since they possess an inner labyrinth organ that supplements oxygen intake.
If a fish floats near the top blowing bubbles more frequently or gulping at the surface, it likely indicates low oxygen levels in the tank. Test and adjust accordingly by changing 10-25% of the water, inspecting filters and aerators, reducing bioload, and removing decaying elements.
While bubbles streaming from the gills generally mean your fish are breathing easy!
Display of Playful Behavior
Aquarium fish often blow bubbles during feeding time or when anticipating a water change or tank cleaning. This shows excitement and an eagerness to explore new items introduced to their environment. Bubbles released while interacting with tank decorations, trailing tankmates, or their reflection demonstrate inquisitive, stimulated behavior (Source).
In bubblenest builders like bettas and gouramis, foamy nests anchor surface-floating eggs deposited after mating. So bubble production can signal courtship, spawning activities, and careful brooding of recent broods. Releasing bubbles is also thought to be a territorial display among breeding males.
All indication of normal zealous energies!
When Bubbles Signal a Problem
Seeing a few bubbles at the top of your aquarium from time to time is normal, but consistent bubbles could mean issues for your fish. There are a few key reasons bubbles form more often than they should.
Gasping at the Surface
If you notice your fish consistently coming up for air and gulping at the surface, this likely means there is not enough oxygen in the tank water. Fish need oxygen just like humans, and will show signs of distress when levels drop too low such as gasping, rapid breathing, loss of color, lethargy, and hanging out only at the top of the tank.
Causes for low oxygen can include overcrowding, high temperatures, low water movement, too much waste buildup, and bacterial blooms. Poor water parameters also inhibit oxygen diffusion. Test and adjust ammonia, nitrites, nitrates, pH, hardness, etc. to ideal ranges.
Increase surface agitation and flow, reduce feeding, gravel vacuum, and perform water changes to help. According to AquariumScience.org, most community tanks should have at least 4-8ppm dissolved oxygen for healthy respiration.
Overactive Swim Bladders
The swim bladder is an internal gas-filled organ that helps fish float at their desired depth without having to constantly swim. Sometimes this organ can become distended or stop functioning properly, causing floating issues.
Affected fish will struggle to stay submerged, end up floating or bobbing up and down, and may gulp at the surface.
Swim bladder disorder can result from gastrointestinal issues, rapid pressure changes, poor nutrition, infections, parasites, tumors, organ damage, and genetic defects according to Aquarium Source. Fixing the root cause is key to resolving swim bladder problems if possible.
Feeding de-shelled peas, keeping water pristine, correcting rapid water changes, and even antibiotics may help in some cases.
Stress or Disease
Unhealthy fish are more likely to hang out at the top of the tank gasping for oxygenated water. Stressors like poor water quality, aggression, overcrowding, improper diet, parasites, injuries or bacterial/viral infections can all cause labored breathing according to Practical Fishkeeping.
The gills, organs, and immune system suffer under chronic stress and illness.
Start by testing water parameters and performing water changes to optimize living conditions. Reduce aggressors and overcrowding, feed high quality varied diets, add stress-reducing décor like plants and hiding spots. Identify and treat any diseases or parasites.
Sometimes euthanasia is kindest for a terminally sick fish.
Conclusion
In summary, fish come to the surface and release bubbles as a normal part of breathing and regulating their buoyancy. Bubbles indicate healthy respiration when fish do so occasionally. However, excessive bubbling or gasping at the surface could signify issues with water oxygenation, swim bladder function or overall fish health.
Understanding the purpose behind this quirky fish behavior can help aquarium owners interpret bubbles as either a natural behavior or a sign of trouble.
