Editorial Feature

Environmental Sensors: Fish Counters

A fish counter is a device used for measuring the number of fishes passing along the river within a period of time. Atlantic salmon is one of the most important species studied using this device.

The fish counter is of three types that include:

  • Resistive counters, which calculate the fish counts based on the difference in resistivities of fish and water.
  • Optical counters, which determine the direction of motion, profile and size of the fish with the help of a pattern of light beam-breaks.
  • Hydrostatic counters that operate using sonar principles.

However, resistivity fish counters are widely used for monitoring fish movements across the river.

Working Method

Resistivity counters are mounted on industrial wires, flow-gauging structures or fish passes. They operate based on the detection of fluctuations in conductivities of the electrodes. When a fish passes over these electrodes, a signal is transmitted to the counter which compares upstream and downstream fish movements by eliminating the signals generated by debris and logs passing downstream.

In some cases, the counter may not determine if the signal is produced by fish, and hence the signals are stored as events. The signal patterns of these events are then analyzed by researchers to identify the cause. In this way, the number of fishes passing through the counter can be analyzed more accurately by the counter.


The fish counter data helps making decisions on managing the fishery by determining the status of the fishes. It is even possible to determine the size and direction of the fish by analyzing the signal.

Products on the Market

Some of the fish counters currently available in market are listed below:

Bioscanner Fish Counter

The Bioscanner fish counter developed by Vaki is a device designed for counting fishes of large and small sizes, from 3 g to 12 kg. Fish of all species are counted in an accurate, fast and reliable manner. It exhibits high capacity of up to 60,000 fish per hour.

The key benefits of bioscanner fish counter include:

  • Low labor cost
  • Accurate information on number of fish
  • High efficiency
  • Accurate feeding quantities.

Riverwatcher Fish Counter

Vaki’s Riverwatcher fish counter is used for monitoring the migration of fishes in lakes and rivers. Different species of fishes can be identified using infrared scanning technology and high resolution cameras. This device measures the size of each fish with more than 90% accuracy. It features a control unit for storing an image of the fish passing through the scanner, so that the counting can be analyzed later.

The key benefits of Riverwatcher fish counter include the following:

  • It provides valuable data for better fisheries management
  • It compares the movement pattern of fish from one year to another
  • It measures water temperature at frequent intervals.


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