Two fish, noses to be precise, were recorded with an underwater camera.

On the hunt for fish
with ultrasound in

20 September 2016

A fish migration aid needs to be well planned 

The example of the new Greifenstein fish migration aid is a good illustration of how meticulously and painstakingly even the smallest details are fine-tuned. For example, the question: "Where to start?" After all, a piece of bank seen from the land is as good as any other, says the layman. So just a stream mouth in the Danube bank ditch and that's the start of the fish migration aid, right?

Experts are a little more precise. What are the flow conditions like? Where do the fish like to stand? Are there preferred spots and if so, for which fish species?

The experts use state-of-the-art technology, for example underwater ultrasound measurement. In principle, this is no different to what is standard for every gynecologist. Instead of cute babies, they look for fish underwater. Depending on where they prefer to swim, the final entry point into the fish migration aid is defined. This is also based on the modern approach of not only opening up a path with a fish migration aid, but also expanding the fish's living and spawning space.

This involves the use of a tried-and-tested device that has not been used for a long time, a so-called "diving barge". A long time ago, this was a kind of underwater lift that was used to guide a diver from a boat to his deployment sites below a power plant. Instead of a diver, a modern ultrasound camera is now installed.

Manuel Langkau and Marc Zeyer from LFV Hydroakustik ( are specialists in sonication for fish. They have installed their monitoring technology on the diving platform. The vehicle is towed by the tried-and-tested VERBUND icebreaker "Röthelstein", which is used for cargo trips along the entire Danube in summer.

The ship Röthelstein is anchored on the Danube under a bright blue sky.

Hooray, a girl! Joking aside: knowledgeable eyes immediately recognize a fish in the electronic ultrasonic point cloud, experts can even identify it by its silhouette or fin shape. As amateurs, we are happy to see the dots at all.