The fish are out of breath

Created: 08/18/2022, 07:00

By: Helena Grillenberger

Test for emergencies: The THW Markt Schwaben practiced the ventilation of a fish pond near Finsing (picture left).

That was not yet necessary in the district.

© THW Markt Schwaben

Heat stress in streams and ponds: the waters become too warm for fish.

So they don't have enough oxygen.

Erding

– Heat and drought have dominated the weather for weeks.

Waters are also getting warmer and the fish suffer from the high temperatures.

"Especially this year it's all very problematic," explains Franz Flieger, chairman of the sports fishing club Dorfen-Altenerding: "Because it's so warm and nothing comes from above."

The amount of water shrinks at the high temperatures and the oxygen content in the water decreases, explains Flieger.

This can be a problem, especially in streams and rivers, because the wildlife living there is adapted to the normally high oxygen concentration.

But the fish are also running out of air in ponds and lakes: "We notice that clearly," says Thomas Schreder, chairman of the district hunting association, passionate angler and qualified biologist: "The fish are in the ponds very close to the surface.

That is always a sign that they need extra oxygen.”

Normally, fish in standing water tend to stay in the deeper regions where it is cooler when temperatures are high.

Instead, if the fish swim upwards, this indicates that there is not enough oxygen in the water, explains Schreder.

Emergency situation: The emergency has already occurred at Berger See near Steinhöring in the Ebersberg district.

Because of the heat and drought, it has largely silted up.

Two cubic meters of fish carcasses have already been collected.

© Johannes Dziemballa

In the Sempt, for example, the most common fish are brown trout, followed by rainbow trout.

This species of fish makes high demands on its environment, the water temperature should ideally be between 8 and 14 degrees.

Around 20 degrees is still okay, 23 degrees would be critical, says Schreder, "and from 25 degrees nothing works anymore.

Everyone is dead there.”

Flieger knows that the carp that can be found in the standing waters in the district have a higher temperature tolerance.

"But they too don't have enough oxygen at the moment."

The stress caused by the high temperatures and lack of oxygen can be life-threatening for the animals alone.

Additional disturbances such as swimmers increase the stress even more, explains Schreder.

Even as a layman, you can make sure to give fish some rest and a shady area.

Premature fishing is currently not planned in the district: "We leave the fish alone," says Schreder.

"The more rest, the higher the chance of survival."

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The Isen is currently an average of 18.3 degrees warm, in August 2021 it was an average of 0.3 degrees less, according to the Bavarian hydrological service.

In the case of the Sempt, it is the level that causes concern: According to the Bavarian flood news service, an average of around 76 centimeters was measured in August last year, so far this year it was an average of 66 centimeters in August.

A similar picture emerges for the ponds in the district, which are usually warmer than flowing water anyway: According to the water rescue service, the Kronthaler Weiher, for example, had an average temperature of 19.8 degrees (19.9 without measured values ​​September).

So far this season, the average temperature is 21.8 degrees.

The THW Markt Schwaben is already rehearsing the emergency and practicing water aeration at a Finsinger fish pond.

This year there was no request, explains deputy local representative Stefan Sandner.

"But of course that can pop up at any time due to the weather at the moment."

When water is aerated, the THW does not cool the water, but only brings in fresh air, i.e. oxygen, and at the same time ensures a little circulation in the water.

This is of existential importance because the fish can no longer breathe above a certain temperature, explains the aid organization.

"In this way, the THW prevents the fish from suffocating," adds Schreder.

"Of course that can be double-edged, so the warm water gets to where the fish can still cool down," he says, explaining why the water should not be mixed completely.

In the long term, explains the biologist, the fish would primarily help in natural waters.