Guided by the light

Several trials have shown that fish have a high stress level at the time of slaughter, which may be attributed to the treatment the fish receive prior to stunning and bleeding. This may include many fish in the seine or reaction to pumping and the reduction of pressure.

Given considerations regarding the prevention of cruelty to animals and fish welfare, as well as the reduced quality of fish meat, producers are interested in finding stunning and slaughtering methods that can reduce the stress level.

Strict requirements for stunning

The new slaughterhouse regulations for fish, which came into force on January 1, 2007, include a requirement that fish shall be anaesthetised prior to slaughtering. The new regulations also ban the use of CO2 in the water as a stunning method. This was the most common stunning method in Norway, and the introduction of the ban was delayed several times pending alternative methods.

A project was commenced to study whether fish could be guided to the stunning and slaughtering processes in a non stressful manner using reflexes or spontaneous reactions. The project, which was financed by the Research Council of Norway and the Fishery and Aquaculture Industry Research Fund (FHF), concentrated on the reaction of fish to light and orientation in relation to water current.

With light in the darkness,

A test rig was constructed comprising two tanks filled with water connected with a four metre long channel. The channel, which was filled with water, was covered with plexiglas, and a current could be added in either direction. It was equipped with light from a laser projector and an array of moveable glows.

The fish entered the channel either from one of the tanks or from a pipe in the centre of the channel. In the channel, the fish were exposed to varying influences: water current from the left or right, laser light or moving glow from the left or right, with or against the water current in different combinations. The trials were conducted in a dark room.

…the glow leads the way

It proved to be difficult to control the behaviour of the fish with laser light, but with the aid of the manually-moved glow it was possible to steer the fish in the desired direction without exposing it to unnecessary stress. The direction of the water current had no impact on the reaction of the fish to the light. The connection between light stimulation and water current, which is described in the project, applies to individual fish. How schools of fish will react has not been tested. It also relies on the fish not having other visual influences, as will be the case under normal light conditions in connection with pumping or slaughtering.

“These results are promising, but further trials are necessary to evaluate an industrial exploitation of this technology,” says project manager and Senior Scientist Kjell Ø. Midling.

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