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Do Fish Need Oxygen? Factors Affecting Oxygen Consumption


Take an in depth take a look at any fish swimming underwater, and also you’ll spot the unmistakable indicators of its gills opening and shutting. You bear in mind your science courses in elementary faculty, so that fish transfer their gills to breathe. However what do they breathe, precisely? 

This looks as if a really intuitive query, however when water consists of simply 1% of dissolved oxygen, it’s a legitimate one. Do fish really want oxygen to outlive? How do they get the oxygen they want? On this article, we deal with these questions and extra.

Spoiler alert: Fish, like all different dwelling issues, want oxygen to outlive.

Why Do Fish Want Oxygen?

Now that we’ve established that every one species of fish do certainly want oxygen, let’s check out what it’s used for. All dwelling issues, fish and vegetation included, use oxygen in a course of often known as cardio respiration. On this course of, oxygen is used to interrupt down meals molecules to launch vitality, which is in flip used to hold out all dwelling processes. Assume consuming, rising, swimming, the works. 

As you could think about, cardio respiration is completely essential to a fish’s survival – and by extension, oxygen is simply too. Nevertheless it’s not simply fish that require oxygen. Nitrifying micro organism do too. Within the absence of oxygen, the nitrogen cycle is disrupted as these micro organism are unable to transform ammonia from fish into nitrates and nitrites. This in flip creates poisonous water circumstances on your fish.

A tank that lacks oxygen would pressure its inhabitants to endure anaerobic respiration. It is a course of that solely produces between 5-8% of the vitality produced in cardio respiration, so it’s not a sustainable technique for long-term survival.

Due to this fact, fish completely want oxygen to outlive. A scarcity of oxygen harms your fish immediately and not directly. Direct implications embody suffocation and stunted progress, whereas oblique implications embody unstable water circumstances and their related diseases.

The place Do Fish Get Oxygen From?

Given the significance of oxygen, it’s value looking at the place fish get oxygen from. Within the overwhelming majority of instances, fish meet their respiratory wants utilizing dissolved oxygen in tanks. It is a course of the place oxygen molecules from the environment dissolve naturally within the water.

The air we breathe consists of roughly 20% oxygen and 80% nitrogen. Nevertheless, solely a small fraction dissolves in water.

In the meantime, for those who maintain aquatic vegetation in your tank, you’ll be able to relaxation assured realizing that oxygen is launched by vegetation as a byproduct of photosynthesis. Due to this fact, housing aquatic vegetation in your tank may be long-term transfer.

Final however not least, some fish don’t have any have to rely completely on dissolved oxygen to breathe. These fish are in a position to inhale oxygen from the environment utilizing labyrinth organs. Should you’ve ever noticed a betta fish taking gulps of air on the floor of the tank, that’s precisely what’s occurring.

Elements Affecting Oxygen Consumption in Fish

A number of components have an effect on the speed of oxygen consumption in fish. Realizing how a lot oxygen your fish wants lets you adequately meet their wants and maintain them wholesome.


Typically talking, bigger fish have a better oxygen requirement. Giant fish are inclined to eat a larger complete quantity of oxygen in comparison with small fish. Nevertheless, smaller fish eat extra oxygen per unit of physique weight, in comparison with their bigger counterparts. 

A examine by Auburn College experiences that 10-gram channel catfish use roughly 1,050 milligrams of oxygen per kilogram of physique weight in an hour, whereas a 500-gram fish solely consumes 480 milligrams of oxygen per kilogram of physique weight in the identical timeframe. 

Nevertheless, these figures present that the 10-gram channel fish would solely eat a complete of 10.5 milligrams of oxygen per hour, regardless of their excessive necessities per unit of physique weight. In the meantime, the bigger, 500-gram fish will use a complete of 240 milligrams of oxygen each hour.


Typically talking, an oxygen stage of 8.3 ppm (parts per million) is ample for many freshwater tanks. It is because most fish species breathe by oxygen in water.

Nevertheless, some kinds of fish have advanced to outlive in low-oxygen circumstances. These species embody aquarium catfish, gouramis, Siamese preventing fish, and loaches.

Many of those fish are in a position to breathe atmospheric oxygen by the blood vessels of their pores and skin, permitting them to thrive in muddy riverbanks with a poorly oxygenated water provide. Others, such because the Siamese preventing fish, have advanced labyrinth organs that enable them to gulp air from the floor of the tank.

Be that as it might, do word that the majority freshwater and tropical fish breathe solely by their gills.

Metabolic Fee 

Metabolic fee measures how a lot meals is being transformed into vitality inside a given interval. The upper the metabolic fee of your fish, the extra oxygen it requires. Typically, your fish will eat a larger quantity of oxygen underneath the next circumstances:

– Proper after a heavy meal

– When it’s bodily energetic

– Throughout copy

These circumstances necessitate a larger fee of respiration, so extra oxygen will probably be used. Metabolic fee can also be affected by temperature, which we’ll talk about under.


Temperature is probably one of many key components affecting oxygen consumption in fish. At low temperatures, fish enter a state of near-hibernation, the place they’re able to survive with minimal metabolic exercise. Which means fish require much less oxygen when temperatures are low.

Nevertheless, issues change quickly as temperatures begin to rise. The oxygen necessities of fish will double with each 50°F improve in water temperature. Heat water can precipitate a rise in metabolism, which means that your fish would require extra oxygen to maintain its life processes.

As a result of fish in hotter fish tanks want extra oxygen, it will be important that you just maintain your system well-oxygenated in the summertime – particularly at night time, when aquatic vegetation cease releasing oxygen.

How To Enhance Oxygen Ranges In Your Tank

Sustaining an sufficient quantity of dissolved oxygen in your tank is essential in protecting it wholesome. We might extremely advocate utilizing oxygen meters to make sure that the oxygen ranges in your tank are as much as mark. A scarcity of oxygen might spell hassle on your fish.

Fortunately, there are some things you are able to do to extend the oxygen ranges in your tank ought to the necessity come up. Right here are some things you are able to do!

Enhance the Floor Space of Your Tank

Oxygen enters your tank through the topmost layer of water, so growing the floor space of your tank is likely one of the most simple methods of accelerating its oxygen ranges. 

While you improve the floor space of your tank, you improve the quantity of water that’s immediately uncovered to atmospheric air, permitting extra oxygen to dissolve in it.

One factor to keep away from about using this technique goes too far. Whereas it may be tempting to focus solely on maximizing floor space, most fish require a snug depth of their aquarium to thrive.

Not all areas of your tank would obtain 100% oxygen saturation underneath these circumstances, however that’s completely regular.

20 Gallon Aquarium

Aerate the Water By way of Floor Agitation

One other method of accelerating oxygen ranges in your tank is by aerating the water through floor agitation. You are able to do so utilizing wavemakers, spray bars, aquarium bubblers, and even Cling-on-Again (HOB) filters. Doing so could make a distinction, as agitated water tends to comprise a larger quantity of dissolved oxygen.

Try this text to be taught the variations between a HOB and a canister filter, as the kind of filter you select will impression its effectiveness in aerating your water. 

These gadgets work by permitting extra water to come back into contact with the environment. Doing so accomplishes two issues: 1. It permits extra carbon dioxide within the water to flee and a pair of. It permits extra oxygen to dissolve in your tank water.

Take into account Decreasing the Water Temperature 

One thing else to pay attention to is elevated water temperature. The upper the temperature of the water in your tank, the decrease its capability to successfully dissolve oxygen. In different phrases, hotter water tends to have much less oxygen.

That is dangerous information for the fishing trade, as international warming is going down at an alarming fee. It’s estimated that for each diploma Celsius (1.8 levels Fahrenheit) of atmospheric warming, the fishing trade would see a lack of an estimated 3.4 million metric tonnes of potential catches.

Given this phenomenon, it’s important so that you can monitor your aquarium water with a dependable thermometer. Completely different freshwater fish may have a spread of most well-liked temperatures, and we advocate sticking to temperature ranges on the cooler (however snug) finish of the dimensions.

You may also recall that fish have a larger want for oxygen because the water temperature will increase. This implies the hole between the quantity of oxygen dissolved in water vs. the quantity your fish requires narrows as temperature rises. This makes temperature management all of the extra vital.

Inventory Your Tank Appropriately

Final however not least, it is advisable to inventory your tank appropriately! An overstocked tank is a recipe for catastrophe, even when it’s crammed with mild-mannered fish.

Give it some thought this fashion: Each further fish you introduce to your tank goes to have its personal oxygen necessities, however there’s solely a lot dissolved oxygen your water can accommodate.

The scenario worsens at night time, when the aquatic vegetation in your tank cease releasing oxygen as a byproduct of photosynthesis and as an alternative, respire utilizing oxygen as effectively. This will increase the demand for dissolved oxygen in your system.

Addressing this downside requires stocking your tank sensibly. The go-to guideline is the “one inch of fish per gallon” rule, however this text offers more in-depth guidelines on stocking your aquarium!

Do Fish Get Out of Breath?

Sure, fish can completely get out of breath if oxygen ranges are inadequate. If so, you’ll doubtless see them gasping for air on the floor of the water, or observe their gills transferring rapidly in an effort to realize extra oxygen.

Nevertheless, you will need to word that fish can encounter gentle ranges of oxygen deprivation with out exhibiting any of the indicators listed above. If oxygen ranges in your tank are inadequate, however not dangerously low, your fish will nonetheless be capable of breathe. Nevertheless, different facets of their well-being, akin to progress, may be affected.

What Does 100% Air Saturation Imply?

At 100% air saturation, the water is holding as many dissolved gasoline molecules as it could possibly in equilibrium.

Due to this fact, a physique of water with 100% oxygen saturation will comprise the utmost quantity of oxygen molecules it could possibly maintain, given the environmental circumstances. 

Does All Water Have 100% Air Saturation?

No, not all water may have 100% air saturation ranges. Low-oxygen areas can typically kind in deeper waters.

How Do Low-Oxygen Areas Kind?

Low oxygen areas can kind in deep waters for a wide range of causes. Initially, photosynthesis is much less more likely to happen in deeper waters just because much less mild is ready to penetrate these depths.

Which means algae and phytoplankton don’t launch oxygen in deep waters, inflicting a lower in oxygen ranges.

Secondly, extra microbial decomposition takes place in deeper waters. The micro organism that break down natural matter require oxygen to take action successfully. Whereas decomposition can happen within the absence of oxygen, this course of is much less environment friendly and may launch a foul odor.


To circle again to the query that began all of it: Sure! Fish undoubtedly want oxygen, and would require completely different quantities of oxygen relying on their species, metabolic fee, and physique temperature.

As a accountable fish keeper, you need to completely be sure that the dissolved oxygen stage in your tank is ample on your fish, as it will impression their normal well being and well-being.

Did you take pleasure in this text? Should you did, share it with another person who may profit from it! 


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