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Can Fish Drown? (How to Prevent It?)

Can Fish Drown? (How to Prevent It?)

Ever wondered if your fish can drown in the aquarium? If so, this detailed article is for you. We will look at what can course your fish to drown and how you can avoid it.

So, can a fish drown? Yes, fish can drown if it lacks enough oxygen in the water. This is as a result of an overcrowded aquarium or if the forward movement of the fish is altered. Equally, warm and foul water results in low oxygen levels, which ultimately leads to drowning.

Want to more about what triggers a fish to drown? Read on for more information.

What causes fish to drown in water?

The main reason why fish drown is the lack of enough oxygen in the water. Depleted oxygen levels in the fish tank are due to several factors such as overcrowding and too many live plants. Let’s look at how each depletes the oxygen leading to drowning.

Causes of low oxygen levels.

Initially, fish will show typical symptoms of low oxygen levels such as inactivity and gasping for air on the water surface. Drowning indicates severe oxygen depletion, which is extremely harmful not only to your fish but the live plants and other useful bacteria.

Excess live plants in a dark aquarium

Naturally, plants use carbon dioxide in the water and give off oxygen, which is vital for fish survival. Unfortunately, too much live plants in a dark fish tank reverse the process. The plants use the oxygen, which leads to the drowning of the fish.

Equally, algae cause the same phenomenon. To protect your little fellas from drowning keep the tank in a well-lit area with, well … not too much live plants.

Excess waste in the water

Excess waste is typically synonymous with overstocking. These two conditions significantly lead to low oxygen levels that are harmful to the fish. Besides, waste in the fish tank provides a suitable breeding ground for explosive algae growth.

This further adds insult to the injury. As such, keeping your tank free of waste and with the right amount of fish is a prerequisite to normal oxygen levels that prevents your fish from drowning.

Increased water temperature

As earlier mentioned, high temperature causes the oxygen in the water to decrease. Warm water rarely holds oxygen for long. If you notice your fish are drowning conduct a temperature test and perform a water change replacing the tank water with cold tap water. Alternatively, you can place ice cubes in the water or blow air on the surface of the water using a fan.

Slow to no water movement

Water movement significantly improves the oxygen in the water. Stagnant water has low oxygen levels since there is no exchange of oxygen in the water column. To address this, install a filter that makes water movements suitable for your fish.

Besides, filters move water from the surface to the bottom of the tank, equally distributing the oxygen. Alternatively, you can use high capacity water filters.

How can you improve oxygen levels in the fish tank?

The oxygen that fish use is not initially from the water itself but rather from the surrounding environment outside the tank. Why? Because the oxygen and hydrogen present in the water are not ideal for breathing.

fish tank oxygen

As such, there is gas exchange at the surface of the tank where carbon dioxide from the water exchanges with the oxygen from the surrounding air. Strange right? As such, we will look at ways through which you can increase gas exchange. Let’s find them out.

Stock the right amount of fish

Yes, every fish you introduce into the tank dents the oxygen levels in the water. Therefore, aim to stock just the right amount to avoid oxygen depletion add apparent drowning of your fish.

Use the right amount of chemicals

The chemicals introduced in the aquarium have a profound effect on the oxygen level. For example, water conditioners can inhibit the circulation of oxygen inside the fish tank. Ensure you follow the instruction to the letter to avoid overdose, which can lower oxygen.

Increase the aquarium surface area

Much of the gas exchange happens at the surface of the water. As such, finding a tank with a vast surface area is a recipe for increased gas exchange, which ultimately leads to increased oxygen levels. Similarly, you should consider the size and shape of the tank for maximum gas exchange.

Increase water movement

Increasing the water movement at the surface of the fish tank increases the surface area where breathable oxygen dissolves in the water while carbon dioxide escapes from the aquarium. So, how can you increase water movement?

Spray bars: these bars sprinkle water back to the aquarium from the filter outlet but at a slow rate. They work efficiently with external filters.

Aquarium bubblers: these bubblers are attached to the aquarium using an airline. The most common types are the air stones that come in different sizes and shapes. Usually, they are attached to the substrate and ornaments.

Powerheads: these are the most common among hobbyists. They are used to increase more water flow on the surface of the water.

Wavemakers: They make waves that mimic those in the oceans and sea. The surge created significantly improves water movement at the surface.

Observe the right temperature

Cold water naturally holds more oxygen compared to warm water. You can shield the aquarium from direct sunlight. Alternatively, you can switch off the heater during warm days or use fans to cool the air.

How do fish breathe?

Just like us humans, fish also need oxygen for them to survive in the water. However, they are equipped with gills that allow them to filter oxygen from the water.

Their respiratory system is well equipped to handle the low oxygen concentration in the water, which is about 6,6ml/l in freshwater are a room temperature of 23 C.

For maximum absorption of the oxygen, the fish combine their mouth (buccal cavity) and the gills opening (opercula) and the covering. This combination presents a low-power but an efficient movement of water across the gas absorption area of the gills.

The hard gill cover offers protection to the delicate gills. The efficiency of the whole process is also bolstered by the large surface area and the thin membranes on the gills. While this is essential, there is a downside to it since to inhibit osmoregulation.

Structure of the gills

They are very complex and contain branchial arches, numerous curved parts that pass through the pharyngeal pouches found on either side and gill filaments that form a V shape structure. The filaments are responsible for producing the gill lamellas.

Lamellas are found in each side of the filament, and there can be at least 40 per mm. It is here that oxygen absorption takes place since they are skinny.

How oxygen is absorbed

When oxygenated water leaves the oral cavity, it reaches the gills and leaves the cavity via the opercula. In the meantime, blood in the lamellas flows in the opposite direction of the water flow for maximum absorption.

Besides, the oxygen level in the blood ought to be less than that of the oxygenated water to increase the rate of diffusion. Once the oxygen passes through the lamellas, the hemoglobin in the blood picks it up, and it is transported across the body of the fish.

Once the oxygen reaches the cells, it seamlessly diffuses in the high carbon dioxide cells. Likewise, the carbon dioxide diffuses in the blood and is transported to the lamellas where it diffuses through the gills. However, some of the carbon dioxides is left in the blood to aid in osmoregulation.

Do fish have other breathing mechanisms?

Yes, in fact, most fry breathes through the skin before the gills can form. As the fish grows, so do the gills form since breathing through the skin is not sufficient. However, only 10-20 percent of breathing happens through the skin for adult fish.

Other species such as loaches can breathe through the intestine. Not to mention those that breathe through the rectum or the mouth. Interestingly, some species do not have a specific breathing channel. For example, the American eel swallows 40% of the oxygen and breathes 60% of its oxygen need through the skin.

Can you drown a fish by pulling it backward?

Yes, this will cause it to drown since the water is flowing on the opposite side. As such, the fish will not be in a position to absorb much-needed oxygen. However, some fish can process reverse movement of water, but, it gets exhausted and drowns.

Secondly, as the fish tries to free itself from the grip, it becomes exhausted. Combining exhaustion and reverse movement of water will ultimately lead to your fish drowning.

Related Questions

How can you tell a fish is suffocating? The fish will reach the surface of the water to gasp for air. Alternatively, he becomes less active and sinks at the bottom of the tank. Equally, he displays darting movements.

Why do certain species of bony fish stay for days without water? Some of them have lungs through which they breathe when out of water. Others use their skin.

Do fish die if they stop swimming?

The average aquarium fish cannot die if it stops swimming. They stop swim when looking at parts of the tank. However, ensure your tank is sufficiently oxygenated. However, fish like tuna ought to swim all their life even when asleep for oxygen absorption.

Do fish suffocate in water? Yes, they suffocate due to low oxygen levels and if they are pulled backward.

Why does a fish die when it is kept out of water?

Well, fish breathe through the gills and not the lungs. Also, their bronchial respiration is equipped to draw oxygen from the water. As such, it is impossible for the fish the use gaseous oxygen making the fish die once out of water. Equally, the gills collapse, leaving no room for diffusion.

Do fish drown when they die?

Most fish are denser than water. As such, they’ll drown once they die. However, over time, the dead fish becomes buoyant due to the gases produced by the decomposing bacteria. While this the common phenomenon, there are exception occasions where the dead fish will decompose at the bottom of the tank.

Why do fish swim sideways in the water?

It is caused by a condition known as swim bladder disease. It is most common in goldfish and bettas but still affects other species of fish in the aquarium. The disorder occurs when the swim bladder gets full.


Typically, the swim bladder/air bladder helps keep the fish buoyant maintaining its depth without floating sideways, upwards or sinking. When full the fish has no balance making it either swim sideways, sink or float to the top. Additionally, their spine might appear curved as the fish tries to keep balance.


The most common cause of swim bladder is overfeeding. The stomach lining press against the swim bladder, causing the condition. It also happens when the fish gulps too much air or when the water temperature is low as this reduces the rate of metabolism.  Additionally, early birth defects, bacteria, and parasitic infections can cause the disorder.


Treating swim bladder is a piece of cake; do not feed him for two to three days because the condition is commonly caused by overfeeding, which leads to constipation. After the third day, feed him with a soft pea. You can soften the pea by boiling or microwave it.

Remove the skin and feed him. It helps clear out the digestive system. Equally, conduct a water change and keep the temperature at 23-26 C. although not recommended, lowering the water level helps the fish reach the surface quickly.


Avoid overfeeding the fish. Secondly, soak the dried food in water before feeding the fish. Equally, keep the water temperature between 23-26 degrees Celsius. Keeping your water clean goes a long way to prevent swim bladder disorder. Side note, the stomach of a fish, is similar to the size of its eye.

Can fish suffocate in bags with water? Yes, over time, the oxygen levels will dip, and the fish will have no oxygen to breathe. Imagine being locked in a tightly sealed room for long, and you’ll ultimately suffocate.

Same happens to the fish. Additionally, if kept for too long in the bag, the buildup of ammonia, nitrites and carbon dioxide will eventually suffocate the fish.

Can fish suffocate in bags without water? Yes, fish can’t breathe without water.

fish in the plastic bag

Can fish die from too much oxygen? No, they are killed by lack of it. In fact, it is impossible to oversaturate the fish tank with oxygen. Why? Because the excess will definitely find its way back to the atmosphere.

Can fish drown in chocolate milk? Yes, if the milk does not have enough oxygen. Fish is not adapted to surviving in milk; therefore, it becomes susceptible to bacterial infections, and also the buildup of ammonia and nitrites will eventually kill the fish in a matter of days.

How long can a fish stay out of the water before it dies?

For average aquarium fish, they’ll take about 5-10 minutes before they die while other species might even take months; especially for lungfish. A handful that breathe through the skin can go for a few days.

Can alkalosis in fish cause suffocation?

Yes, if left untreated the mucus might fill the gills. Additionally, they can deteriorate to an extent where the gills can no longer function, leading to suffocation.

Alkalosis is a disease that causes a buildup of excess mucus on the fish skin leading to inflammation and bleeding of the gills. The fish shows signs such as jumping out of the water, darting movement, gasping for air at the surface and increased respiration.


The fluctuation of pH levels causes the disease. A typical tropical aquarium fish is adapted to water pH of 6.0 to 8.0. If the pH drops below 6.0 acidosis might develop while pH levels more than 8.0 leads to the erosion of the gills and skin.


If the fluctuation is constant, conduct thorough and continuous pH tests. Alternatively, you can purchase products in a pet store that either low or raise the pH level in the tank.

Can gill flukes cause the fish to suffocate?

Yes, too many flukes in the gills can rapidly destroy them inhibiting fish breathing behavior. Also, they lead to secondary infections that go a long way to inhibit fish’s immune system. Newly introduced fish is responsible for gill flukes in a tank.

Gill flukes affect most community fish tanks. They are very harmful to your fish and reach a maximum size of 0.3mm. They usually lay eggs in the gills and affect specific species. Those harmful to Koi fish might not be overly harmful to bettas.

In fact, due to the reaction between them and the gill worms, there is the formation of a mucus substance that can suffocate your fish. The fish also shows symptoms such as increased respiration and darting movements.

If the condition persists, treat the fish with anti-worm means. Additionally, make sure water parameters are kept as recommended.


From the above discussion, we can conclude that a fish can drown in water. And the chief reason for this is lack of enough oxygen. Additionally, diseases such as gill flukes and alkalosis can cause your fish to suffocate. To avoid suffocation/drowning, keep your tank clean, and provide amble oxygen sources.