In several areas along the Norwegian coast local fishermen asserts that wild cod have changed their migratory behaviour following establishment of salmon farms, and no longer enters their natural spawning grounds in the fjords.
Chemical stimulants are important to the individual fish's conception of the surrounding environment. High density stocks of fish in a farm may be expected to release an overwhelming amount of water borne information. If the asserted change in behaviour of wild cod populations can be linked to establishment of salmon farms, water-soluble odorants are then likely candidates to explain such a connection.
The present laboratory experiments were conducted to test behavioural responses in immature and mature wild Atlantic cod exposed to water containing metabolites and waste from farmed salmon. The trials were conducted on single fish in a multiple chamber preference system.
The results show that wild Atlantic cod chose to spend more time in chambers without addition of water from the salmon tank, regardless of their maturation status. The avoidance is probably due to presence of chemical compounds with olfactory properties from salmon, since the added water seemed not to change the water quality in other respects.
The observed behaviour of the cod returning for short irregular trips to the zone with treatment water added, could reflect a learning behaviour. The results do not preclude observations that cod change their behaviour in areas with fish farming activity, further that the olfactory sense is a strong candidate to mediate such a response.