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Many garden pond owners are familiar with this phenomenon: the fish suddenly swim to the surface of the water and gasp for air. When the behavior occurs for the first time, many people do not know why the fish are doing it and if there is a problem. With this gasping for air, the fish indicate that they are suffering from a lack of oxygen. In this article you can find out what the reasons are and how you can eliminate them.

respiration in fish

Just like humans, goldfish need oxygen to survive. However, fish do not take the oxygen from the air, but filter it from the water. Fish have gills instead of lungs. When the fish opens its mouth, water flows in and out through the gills on the side behind its head. The water flows past the thin leaflets of the gill arches, which are heavily supplied with blood. Here the oxygen penetrates through the reddish skin of the gills into the blood vessels. The water and the excreted carbon dioxide then exit the gills through the gill covers.

Goldfish in the pond

Catch a breath

Causes of gasping

In order for the fish to get enough oxygen, the gills must be constantly flowed through with water, because there is significantly less oxygen in the water than in the air. If the oxygen content in the water is too low or if the gills are not fully functional, the fish threatens to suffocate. Therefore, it swims to the surface of the water and gasps for air, which then flows through the gills and comes out again as smaller bubbles.

1. Oxygen level in water too low

If your goldfish gasp for air in summer, the oxygen content in the water is probably too low. There can be different reasons.

  • very high temperatures (the higher the temperature, the less oxygen dissolves in the water)
  • too few plants in the pond (do not produce enough oxygen)
  • Too many fish (consumes too much oxygen)
  • Decay processes in the soil (consume oxygen)
  • the filter does not work properly (rotting processes or insufficient flow)

2. Disease of fish

If only individual fish in the garden pond are affected, it is reasonable to assume that there is a problem with the oxygen uptake of these fish. As a rule, gill problems lead to violent gasping. The following diseases are possible for this.

  • gillworms
  • Parasites on the gills (ichthyo, velvet disease or epitheliocystis)
  • Chemical burns on the gills due to too low a pH value

First Aid Measures

If the goldfish gasp for air, quick help is needed. Otherwise a fish kill is inevitable. A diaphragm pump makes sense as an immediate measure to increase the oxygen content in the water. Many people know this pump from aquaristics. It is connected to a hose and an air stone through which fine air flows through the water. You should also introduce fresh tap water into the pond. Another measure is to put oxygen tablets in the water. Initially, these steps should be enough to increase the dissolved oxygen concentration to the point that none of the goldfish are in danger of death.

Goldfish need enough oxygen

Further measures

A so-called oxidizer can be installed to ensure that the oxygen concentration does not fall below a critical level again after a short time. This is installed at a depth of about 60 cm in the shallow water zone of the pond. The device works on a chemical basis. It contains a cartridge of hydrogen peroxide, which breaks down into water and oxygen. There are no products or residues that can be toxic. Also, an oxidizer works without electricity. So you don't have to lay any cables or hoses first. As soon as the cartridge is empty, the device comes to the water surface by itself and can be refilled.

Improve pond climate

However, the immediate measures mentioned above cannot represent a permanent solution. In principle, something is wrong with the concept of the garden pond. Because if the pond had been carefully laid out and equipped with sufficient quantities of floating and underwater plants, such an undersupply of oxygen should not normally have occurred. The task now is to correct the mistakes as best as possible.

1. Fish stock

A medium-sized fish, such as a goldfish, golden orfe or smaller koi needs about 1000 liters of water. One cubic meter is added for the aquatic plants. Smaller fish such as sticklebacks require less water.

  • You shouldn't put any fish in a 1000 liter plastic pond
  • a pond with 10 m³ should not contain more than 9 goldfish

2. Shading

So that the garden pond does not heat up too much in summer and the oxygen content drops sharply, at least one third of its surface should be in the shade during the midday hours. This can easily be achieved afterwards by taking the following measures.

  • plant high-growing grasses such as bamboo or Chinese reed on the south bank
  • Plant conifers on the south bank
  • add water lilies or floating leaf plants
  • these should cover another third of the surface
garden pond

3. Use aquatic plants as oxygen suppliers

From a water depth of 50 centimetres, the garden pond should be densely populated with fine-leaved aquatic plants. These underwater plants not only produce oxygen, but also contribute to the purification of the pond basin due to their high nutrient consumption. The following is suitable for this.

  • chickweed
  • waterweed
  • thousand leaf

preventive measures

General care measures are necessary so that the fish do not suffer from a lack of oxygen again after a short time and gasp for air on the water surface.

1. Feeding

Fish should only be fed as much as they can eat immediately. Otherwise food residues will collect on the bottom of the pond and rot there. It is therefore essential to check the feeding quantity and only use fish food that is suitable for fish stocking.

fish food

2. Prevent digested sludge on the pond bottom

Withered or withered plant parts (including underwater plants) must be removed regularly. If sludge has already formed on the bottom of the pond due to dead plants, it must be sucked off using a pump. Dead leaves that have fallen into the garden pond should also be fished out promptly.

recognize illness

Identify and treat diseases of the gills

In some cases there is enough oxygen in the water, but the fish cannot absorb it. Since the fish absorb a large part of the required substances from their environment via the gills and release others, the gills are constantly exposed to external attacks: fungi, bacteria, viruses, worms and other parasites. If the gills of the fish are not fully functional, there is also a lack of oxygen. As a rule, not all fish become ill at the same time, which is why individual fish gasping for air on the water surface are the first indication of an illness.

Goldfish breathe through gills

External symptoms:

  • changed gill color (red or pale)
  • Gills are slimy
  • white-grey dots or spots on the gills
  • missing or severely swollen gills
  • Gill covers are permanently protruding or are constantly closed

behavior of the fish

In addition to the conspicuous gasping for air at the water surface, affected fish also show the following behavior.

  • rapid gill movement (rapid breathing)
  • the fish are very sluggish
  • Fish don't eat
  • staggering movements when swimming
garden pond in the garden


With timely diagnosis, most diseases of the gills in fish are curable. Various preparations, for example against bacterial infestation or gill worms, are available in specialist shops.

Check water quality

Ideally, the water quality is also checked. If the ammonia or nitrate levels are too high, the amount of food should be reduced. In addition, if the values are very high, it is necessary to carry out heavy water changes and also to pump out the sludge on the bottom of the pond. Since poisoning with ammonia or nitrite is much worse for your health than too much fresh water, in extreme cases up to 75% of the water can be changed several times a day. Tests are available in specialist shops that even a layman can carry out quickly and easily. It is best to test the pH of the water at the same time. If this is significantly too low (acidic), the mucous membranes of the fish can be corroded and thus no longer function properly.

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