Raising fish in tanks that contain hiding places and other obstacles can make the fish both smarter and improve their chances of survival when they are released into the wild, according to an international team of researchers. “It’s a key problem in that we are very good at rearing fish, but we’re really not very good at releasing those animals in the wild such that they survive,” said Victoria Braithwaite, professor of fisheries and biology, Penn State. “There’s a mismatch between the way we raise them and the real world.”
Juvenile Atlantic salmon raised in tanks that including pebble and rock hiding places and floating artificial plants were better able to navigate mazes and showed signs of improved brain function compared to the salmon reared in standard hatchery tanks, Braithwaite said. This may help conservation fish hatcheries raise and release fish that are better adapted to survive in the wild.
Conservation fish hatcheries raise cod, salmon, trout and other types of fish and release them in places where their species may be threatened, or where their populations are declining.
“The philosophy of most fish hatcheries is to rear a large number of fish and hope some survive,” said Braithwaite. “What this study is suggesting is that you could raise fewer, but smarter fish, and you will still have higher survivability once you release them.”
The researchers, who released their findings today (July 31) in the Proceedings of the Royal Society B, placed pebbles and rocks at the bottom of the tank and added plastic plants weighted down so they would float vertically in the water. Braithwaite said the objects created a more natural, three-dimensional ecosystem.
“In the hatchery the world is homogenous, life is boring and monotonous,” Braithwaite said. “The water flow is the same, you don’t have to find your food and you don’t have to avoid predators.”
The researchers also moved the objects around about once a week during the eight-week study, which took place in Norway.
When the researchers placed the salmon in a maze, the fish raised in the enriched tanks made fewer mistakes when trying to escape the maze, Braithwaite said. The performance of the salmon from the enriched tank continued to improve with each trial, and they learned to solve the maze much faster than fish reared the standard way. Read more….