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The researchers says that fish can find loud noises and unexpected movements stressful, which can adversely affect their physical health. They also say that density at intensive farming facilities may lead to stress and decelerated growth.

The studies indicate, however, that a positive and durable effect can be achieved on the behaviour of pike perch (Sander lucioperca) in situations of stress by adding a long-chain non-saturated omega-3 fatty acid (DHA) to their normal animal plankton feed while they are still in their larval stage.

“Stress is one of the principal obstacles to streamlining the production of pike perch. But the fact that larvae and fry on a DHA diet react and swim more quickly than pike perch reared on feed without DHA seems to indicate that administering the right nutrition as early as the larval stage make the pike perch more robust,” explains Ivar Lund, Project Manager and Senior Researcher at DTU Aqua.

DHA-feed makes the growing pike perch better able to adapt to conditions at fish farms. There is broad consensus that DHA has a positive impact on the early neural development of learning capacity in both people and animals, and a previous study by the same team of researchers demonstrated that pike perch larvae given feed with a low DHA content for a limited period of time simply developed smaller brains.

“We don’t know precisely which parts of the pike perch’s brain benefit from DHA, so we will need to carry out additional studies involving a greater number of fish and clearer focus on the neural effects in the brain if we are to test the correlation between nutrition and behaviour,” explains Ivar Lund. This will be carried out in the new EU project DIVERSIFY, involving six new species in aquaculture.

The pike perch was chosen for the study because it has proved to be extremely sensitive to stress compared with other species of fish reared in aquaculture facilities.