Image caption The results mirror those seen for birds and mammals

Captive-bred fish will do better when released into the wild if they are reared in an interesting environment, according to a Norwegian study.

Salmon reared in stimulating environments, rather than bare fish tanks, showed increased brain power

The results mirror links seen between environment and brain function for birds and mammals.

The fish showed improved spatial learning and cognitive ability, the Royal Society journal study says.

Providing an environment containing pebbles and synthetic floating weed for the fish appeared to promote their intelligence.

One-year-old salmon were raised in either plain fishery tanks or tanks containing an "enriched" environment as part of the study. Those raised in the enriched environment showed significantly better abilities to navigate their way out of a maze, and their forebrains had higher levels of the genetic material associated with spatial awareness.

Previous studies of mammals bred in captivity have shown that stimulating environments aid their development and improve their life chances if they are released into the wild, but this is the first time that the same effects have been seen in fish.

School for Salar the Salmon

Juvenile wild-strain Atlantic salmon (Salmo salar) were used in the study, and changes were seen in the messenger RNA in their brains - which has previously been linked to increased spatial learning ability - after they had enjoyed a life of exploring pebbly tanks with floating and secured plastic fronds.

They outperformed fish raised in a non-enriched environment in subsequent cognitive tests and the differences becoming more pronounced the longer they had been kept in an enriched environment.

The researchers claim that tank enrichment leads to superior spatial learning abilities. The study reveals that fish show the same sorts of links between brain development and spatial behaviour seen in other vertebrates such as mammals.

The story of the Atlantic salmon was given a fictional treatment by Henry Williamson in his anthropomorphised novel Salar the Salmon, and maybe these results bring our understanding of the salmon closer to Williamson's.

Atlantic salmon return to their exact place of birth to spawn

They can live in freshwater and in saltwater oceans

They are found in the northern Atlantic Ocean BBC Nature: more information on Atlantic salmon

The early-rearing environment for fish may be important in fish conservation strategies. The authors suggest that enriched fish-rearing environments lead to flexible behaviour, decreased aggression, flexible shoaling responses, social learning and the ability to recover from stress more quickly, all of which are likely to lead to increased post-release survival in the wild.

Dr Toby Carter, a behavioural biologist at Anglia Ruskin University who has written independently on the Atlantic salmon, commented: "Fish are vertebrates and a lot more complex than many people think.

"More and more evidence is emerging to show that fish have some of the same sorts of neural pathways as other vertebrates like mammals. It is challenging to demonstrate a link between environmental complexity and spatial learning in fish and the experiments reported here are significant."