On a cloudy day a few years ago, Heikki Hirvonen sat on the banks of the River Varisjoki. As he watched its high, fast water sluicing through Finland’s remote northern spruce forest, his mind drifted back to the year before, when the river was almost dry. He thought of the juvenile salmon he’d then released into a nearby stream, hoping they would one day return from the ocean to spawn.
And then he did something remarkable. He stopped thinking like a human, and began to think like a fish.
By looking at the world around him as a fish might, Hirvonen, a behavioural ecologist at the University of Helsinki in Finland, had come to realise that the salmon he bred lived, until their release, pretty dull lives. Raised in barren tanks, they swam in water that flowed at a constant, sluggish rate. They ate the same food pellets, at the same time, each day.
Having so little to do, he pondered how woefully unprepared they must be for the wild future that awaited them; a world of turbulent, ever-changing rivers and oceans, where young fish must learn to eat and not be eaten, where they must learn the deadly art of survival.
Hirvonen, like other scientists, has come to question how fish are raised in hatcheries. Every year, all around the world, billions of these hatchery fish are released into the wild to bolster dwindling wild populations. Typically, less than seven of every 100 survive.
Could that be, some of these scientists are increasingly wondering, because these fish learn so little during their upbringing? Do young fish need to be motivated and intellectually stimulated?
In short, do they need to be entertained?
And could enriching their lives, and teaching them new skills, be key to the survivorship of countless individuals, and even the very future of a few endangered species?
Fish aren’t stupid
It is unsurprising that people forget to think as a fish.
Fish are hard to relate to, says Culum Brown, a childhood snorkeler who grew up to raise and study fish and their behaviour at his laboratory at Macquarie University in Sydney, Australia. They aren’t expressive, we hear little of the noise they make and can’t read their faces. Such prejudice has limited the amount of money spent on fish conservation, and led to a dearth of research into fish cognition, perhaps explaining why we tend to think of fish as stupid, citing anecdotal research that they have no more than a three-second memory.
“They’re a lot smarter than that,” says Victoria Braithwaite, a biologist at The Pennsylvania State University in University Park, Pennsylvania, US. Research is slowly revealing that fish can make friends and use them as allies when hunting, engage in tool use, a trait once attributed only to “higher” species such as humans and birds, and store information for several days or more. Fish from coral reefs and rocky shores that have to actively hunt for a living tend to be more intelligent than fish from duller environments, Brown adds.
Yet despite mounting evidence that captive fish are capable of learning basic life skills before entering the wild, hatcheries across the globe continue to measure success in the number of fish released. “Every year in Australia, the fisheries minister gets up and says something like, ‘This year, we released 15 million fish from hatcheries,’” Brown says. “Everyone thinks, ‘Wow’.” But it’s the number that survive that counts. And that’s where learning how to entertain fish comes into its own.
A tale of two fish
Anne Gro Vea Salvanes, a behavioural ecologist at the University of Bergen in Norway, tells a tale of two fish she has studied.
One juvenile salmon navigates a maze with four cup-shaped exits on one side. Three exits lead to a dead end. The little fish swims into one cup, hits a dead end, and tries another cup before successfully escaping (see video. Credit: Anne Gro Vea Salvanes et al). A second juvenile fish swims into the same dead end repeatedly, never to escape (see second video. Credit: Anne Gro Vea Salvanes et al). The clever fish, Salvanes says, was raised in a hatchery with rocks, pebbles, and plastic plants, adornments that provide mental stimulation. The dumb fish was raised in a bare tank, the usual environment for billions of hatchery fish.
When Salvanes and her colleagues examined the fishes’ brains, they found that the fish raised with adornments had increased brain activity in a region linked to spatial learning.
It would seem simple then, to embellish fish tanks the world over. But adding rocks and plants has a drawback - they get covered in food pellets and fish excrement, making tanks difficult to clean and encouraging bacteria to grow. That raises the costs of rearing fish, damaging the profits of commercial hatcheries.
Some researchers have started experimenting with items that can be easily removed and cleaned or discarded.
Joacim Näslund, a graduate student at the University of Gothenberg in Sweden, adorned tanks at a hatchery in Norway with plastic pipes and shredded plastic bags.