Playgrounds prep fish for life in the wild
PENN STATE (US) — Fish that grow up in tanks with hiding places and other obstacles are smarter, which improves their odds of surviving in the wild, say 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,” says Victoria Braithwaite, professor of fisheries and biology at 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 says. 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,” says 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 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 says the objects created a more natural, three-dimensional ecosystem.
“In the hatchery the world is homogenous, life is boring and monotonous,” Braithwaite says. “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 says. 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.
The brains of the fish from the enriched tank were also different from the fish raised in the standard hatchery tanks, according to the researchers. They noted increased expressions of a gene in a region of the fish’s brain that is associated with learning and memory, an indication of increased brain function and growth. The fish raised in standard tanks did not show this sign of increased brain development.
Interacting with the environment can influence gene expression in the brain, Braithwaite says.
“The brain is a very plastic organ, it’s a dynamic structure,” says Braithwaite, who worked with researchers from the University of Bergen and Uni Research, Bergen, both in Norway.
Braithwaite says the enriched tanks created significant improvement in the intelligence and adaptability of the fish, but were relatively inexpensive and easy to implement. Owners of fish hatcheries should be able to afford the creation of enhanced tanks.
The Research Council of Norway supported the work.
Source: Penn State
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