We can be guilty of thinking that oxygen is a uniquely human need. While all land-dwelling animals breathe oxygen from the air, fish need oxygen too. Not only this, but fish can run out of oxygen, something we humans don’t need to worry about.
Here we’ll look at why fish need oxygen in the water, and how they obtain it from their environment. For fish owners, we’ll also look at how you can support your fish to ensure they are getting the oxygen they need.
The Basics of Fish Respiration
Oxygen is essential for all life as you need it for cellular respiration. This is a process which allows all organisms to convert nutrients from food into energy. Without enough oxygen, fish cannot live and without enough of it, their growth, reproduction, and movement can all be stunted.
Unlike humans who use lungs to breath air, fish have gills. Whereas we can use the oxygen that is in the air, fish need to extract it from the water. These organs are designed to maximize oxygen absorption, but not all gills work in the same way.
Some fish require water to continuously flow over their gills, whereas others can extract oxygen whilst staying still. Some fish can even breathe water from the surface using a specialized organ. Whichever way they do it, oxygen is as vital for fish as it is for humans and a lack of it is a common reason why aquarium fish die.
Why Dissolved Oxygen Matters
It’s crucial to know that fish do not get oxygen from water molecules. As you probably know, a water molecule is H2O, meaning that it has two hydrogen atoms and one oxygen atom. However, fish cannot split these molecules and get oxygen from them. Instead, fish get oxygen that has been absorbed into the water.
Air contains around 21% oxygen but for water, this is usually less than 1%. Due to this, for fish to breathe they need to have oxygen continuously dissolved into the water. Vitally for fish, they can consume more oxygen than gets dissolved, eventually suffocating.
The amount of oxygen in water can vary based on a wide range of factors. For example, cold water can hold more oxygen than warm water. Other factors include altitude, water movement, photosynthesis, decomposition, pollution and depth.
The Dangers of Stagnant Water
The biggest takeaway to know is that stagnant water is the enemy. As long as you keep the water moving and your tank well maintained, your water will stay oxygenated. This is because the greater the surface area, the more oxygen absorption. Moving water will always ensure there is a new water surface for more dissolution.
Stagnant water can also be dangerous for other reasons. It can increase the bacteria levels in the tank, and bacteria also consumes oxygen. Added to this, stagnant water is often linked to an increase in organic matter, making the problem even worse.
Finally, the oxygen will often sit at the surface with lower levels of the tank not getting the nutrients it needs. Organic material, oils or algae can also accumulate at the surface of the water, blocking oxygen absorption.
The Negatives of Low Oxygen in a Fish Tank
By now, you’ll know that the obvious negative of a lack of oxygen is fish death. However, low oxygen will start negatively impacting your fish long before they die. As soon as that oxygen drops, your fish will start to get stressed.
Stress isn’t something you should be putting your fish through, as it can lead to health issues. Their immune system will be weakened, and insufficient oxygen can lead to long-term organ damage. Even if you solve the oxygen issue, your fish can still take time to recover.
A fish tank has an ecosystem, and this can collapse without oxygen. The breakdown of waste and organic matter will halt, and toxins will rapidly rise. This further exacerbates the oxygen issue, and it becomes a vicious cycle until it’s broken.
Signs Your Fish Tank is Lacking Oxygen
If you’re worried about the oxygen levels in your tank, there are a few signs to look out for. The most obvious sign is fish gasping at the surface. They will rapidly open and close their mouths, desperate to breathe.
However, it’s important to note that some fish breathe at the surface, even in a well oxygenated tank. Examples include bettas, gouramis, and corydoras. With these fish, it’s important to observe their behavior as see is they are gasping at the surface more than usual.
Another common behavior in low oxygen tanks is for fish to cluster around the filter. This is because water movement will be stronger with a greater chance of dissolved oxygen. You may also notice rapid gill movement, as they work harder to extract oxygen.
The last sign to look out for is slow and lethargic movement. When in poor health, fish will slow down and not be as fun to watch as usual. Whether low oxygen or not, lethargy is never a good sign with your fish and usually indicates there is some kind of issue.
How to Increase Oxygen in a Fish Tank
As we’ve seen, the key thing is to keep your water moving. The easiest way to do this is to have a filter that disturbs the surface. Most standard filters will do this, but there are also air stones and pumps that create a continuous stream of bubbles that rise to the surface.
It’s best to double check the filter is suitable for your tank. If it’s underpowered, it may not have the flow rate required for your water volume. Also ensure your filter is maintained, as if filter media gets full, it’s efficiency will be reduced until it is cleaned.
The other great way to increase oxygen is through water changes. The water you introduce will not only be oxygen rich, but it won’t be full of waste. You just want to ensure the water is at the correct temperature and has been properly treated.
Live plants are also a great choice, as they will produce oxygen throughout the day due to photosynthesis. Finally, avoiding overcrowding your tank as having too many fish can make keeping oxygen levels high extremely difficult, among other issues.
