Fish Protection Technology

Eledtric Fish-Repelling Systems


Our Electric Fish Repelling Device emits pulses of electric current into the water. The electric pulses and their frequency cause muscle contractions to the fish. The fish interpret these contractions as a danger and they swim away from the area to escape.

Unlike other Electric Fish Repelling Devices, our system emits short polarity-changing sequences, which prevent fish moving towards our anodes (galvanotaxis)

fish repelling system

An effective repelling field must fulfill the following minimum requirements:

  • Optimum increase of the field power.
    Paralysis of the fish can occur if water currents and natural fish movement lead fish into areas where field power is rising too rapidly. However, if the field power is increasing too slowly the fish cannot realize in which direction the field power is decreasing, they can become lost and are unable to find the "exit".
  • Precisely delivered pulse frequencies.
    Pulse frequencies which are too low are not realized by the fish.
    Pulse frequencies that are too high lead to strong muscle movements and the fish are prevented from swimming and escaping.
  • Exact adjustment of field lines.
    Fish react to the field by orienting their bodies in such a way that they receive the lowest potential difference. By adjusting the field lines the fish can be steered away from the area to be blocked.
  • Optimized pulse shape and pulse duration.
    Short or not well-shaped pulse frequencies may not be recognized by fish.
    Long pulse frequencies may paralyze the fish.
  • Homogeneous field design along the total width and depth of the inlet, as fish will find every loophole in the field.
  • Even in case of different water conductivity and variable water levels all these conditions have to be taken into account.
    The design and layout of our Fish Repelling System includes a detailed evaluation of site criteria, including:
  • Profile of the water flow
  • Dimensions of the water intake structure
  • Conductivity of the water
  • Type and size of fish present

We have developed unique optimization software, which determines optimum electrode location and pulse magnitude and frequency, for each installation site. This assures each system is tailored to the customers' requirements

Automatic Fish Return System


band creen chamber

Fish Return Systems can easily be retrofitted to our Screening Machines. Fish Return Systems include specially developed buckets mounted on each screen panel. The buckets transport fish, cyclostamata and other valuable species in front of the screen panels to a water filled trough. The trough is then lead to an area where the fish can be returned to the water source. The various illustrations shown in this chart demonstrate the different ways of emptying the fish buckets.

The sophisticated MultiDisc® technology can also be adapted to include special provisions for gentle fish recovery. Due to the rotation of the screening panels on a MultiDisc® the fish buckets are emptied directly into the return trough, with a low drop height.

Fish return troughs and debris troughs can be independent or combined based on customers' requirements.

Another option for gentle aquatic species protection is the use of the Geiger Traveling Band Screen with Fish Protection Provision. Here also the emptying of the fish buckets can be done independent from the debris trough. The special design features of the machine also ensure a low drop height.

Inadvertent fish mortality in screening plants can be significantly decreased by adding our fish return system to the Geiger Traveling Band Screens with in-to-out, or out-to-in flow patterns. When possible it is better to use the Geiger Traveling Band Screens with in-to-out flow pattern, because the fish are never dewatered. Existing Traveling Band screen machines installed at screening plants can also be equipped with fish buckets. However, due to the special design parameters very high drop heights may exist and there is no possibility to separate debris from the fish buckets

Eledtric Fish Immobilization System


fish return system

1. Field of application

Fish Immobilization Systems are only used in connection with Fish Return Systems. The Fish Immobilization systems are located at the inlet chambers and prevent fish or cyclostomata from avoiding a Fish Return System. The system is used when it is likely that fish trying to avoid a Fish Return Ssystem may exhaust themselves.

2. Function

The immobilization of the fish and cyclostomata in the inlet chamber is accomplished by the emission of short electric pulse sequences. The fish become momentarily immobilized and are then easily caught into the fish buckets of our rotating screen.

3. Requirements

A Fish Immobilization System has to fulfill the following requirements:

  • The entire area must feel the effect of the electric pulses. If there are variations in the field power, the Fish Immobilization System will function like a Fish Repelling System
  • Precisely delivered pulse frequencies and field power to match the kind and size of fish.
  • Gradual increase of pulse shape and pulse duration. Short or not well-shaped pulse frequencies will not immobilize the fish, pulse frequencies that are too long may paralyze the fish.fish bucket
  • All of these conditions have to be taken into account, even in case of different water conductivity and variable water levels

For the mechanical as well as for the electro-technical design of a Fish Immobilization System many criteria must be taken into consideration, including:

  • Flow profile
  • Dimensions of the water intake structures
  • Water conductivity
  • Type and size of fish
  • Design and arrangement of the fish return system

We have developed a special optimization software, which determines exact positions of the electrodes and pulse frequencies, specifically tailored for each customers site.