1 fish, 2 fish, smart fish, sly fish

Goldfish don't forget every time they swim around the bowl. Fish - the smarter ones at least - have been shown to distinguish left from right, to remember mental maps of their surroundings, sometimes for months, use logic, engage in deception, and cooperate while hunting.

We humans have grudgingly come to accept the idea that our close relatives the chimpanzees can think. And maybe our best friend the dog. But fish? They're not even warm-blooded.

We may tend to underestimate fish as "lower" creatures thanks to the residue of an ancient idea known as the great chain of being - a quasi-religious notion that all living things form a hierarchy from lowest to highest.

Though Charles Darwin sometimes referred to higher and lower animals, his theory replaced the great chain of being with a branching bush of life. In Darwin's version of evolution, fish aren't any less evolved than we are.

Some fish probably evolved intelligent behavior because they lived in complicated environments where it benefited them, said University of Neuchatel biologist Redouan Bshary. "Fish brain structure is more primitive than that of mammals, but they've still had 400 million years to evolve something with it," he said. "There's no a priori reason why fish should remain stupid."

One of the researchers most responsible for revealing the minds of fish is Victoria Braithwaite, whom I first met at dinner during a recent visit to Pennsylvania State University, where she is a professor of biology. I made the regrettable choice of ordering the salmon, which is, I now realize, one of the smarter fish.

Braithwaite is the author of the 2010 book Do Fish Feel Pain?, to which her answer is a definite yes.

She started out studying salmon, trying to figure out how they navigate. She realized nobody had really looked at the cognitive abilities of wild fish.

So she and a colleague started putting fish into mazes to see what they could do.

"We were flabbergasted by what they were able to achieve," she said. Several strategies emerged. Species at home in ponds noted small landmarks such as plants and rocks. Those used to streams ignored these, since such small objects are likely to be swept down current.

Many fish know left from right. Some species turn their right side to new objects, she said, thus sending the information into the left hemisphere, showing how parts of their brains are specialized. When encountering familiar objects, they look with their left eyes and process with their right brains.

And fish can have good memories for other fish. In one set of experiments, researchers isolated an "observer" fish that watched two others fighting. When the observer was put in with the fighters, he remembered the outcome and behaved accordingly: submissively to the winner and more aggressively to the loser.

Fish can also use logic, Braithwaite said. Some species figure out that if A can beat up B and B can beat up C, then A can probably beat up C. That's called a transitive inference and people don't learn to do that till they're about 4.

This is not to say all fish are equally smart. There are 30,000 species of fish. Some don't seem too bright, but sticklebacks are smart, and so are goldfish, Braithwaite said.

In his work on coral reefs, Bshary found that groupers are so smart they can enlist eels to help them hunt. Groupers can also outswim most prey fish in open water, but a prey fish can escape by entering a crevasse in a coral reef. When that happens, a grouper will come up to the cave of a moray eel and shake its head to get the eel's attention.

That sometimes prompts the eel to swim with the grouper to the spot where the prey fish disappeared. The grouper uses its snout to point to where the fish went, and the eel slinks down into the hole. About half the time the eel eats the fish, but the other half of the time, he flushes it out and the grouper eats it.

Fifty-fifty odds are better than none.

Bshary also found that the small, parasite-eating cleaner wrasses are downright Machiavellian in their ability to con "client" fish into expecting a parasite removal service. The wrasses perform this service just enough to get a good reputation and then they take a bite of a client - thus supplementing their diets.

One scientist who is not surprised by these fish feats is Jennifer Mather of the University of Lethbridge in Canada, who studies cognitive skills of the octopus. Not only are these creatures cold-blooded but they aren't even vertebrates, and yet, Mather said, they can unscrew jars and even, with the right reward inside, undo childproof caps on pill bottles.

Octopi also play, she said. When a water jet introduced a current in a tank at the Seattle Aquarium, one playful octopus repeatedly pushed a pill bottle against the current so it would keep returning, prompting one of Mather's colleagues to exclaim that "she's bouncing a ball."

Braithwaite has also done experiments on pain, injecting bee venom or other irritants into the lips of fish. That changed the fish behavior by preventing them from paying attention to new objects. They acted pained, and their behavior returned to normal when given morphine.

Does this mean fish are conscious?

Consciousness is a slippery concept for us as well as for animals. From her experience, Braithwaite says she's convinced fish are aware of their surroundings. And some can create mental images.

Knowing all this, she said, she doesn't disapprove of eating fish (though I noticed she ordered a vegetable flatbread), but she said we shouldn't discount the pain they feel when they're dragged up through hundreds of feet of water until their eyes explode, or left to suffer alive on the deck of a fishing boat. "There are methods you can use which can make that kill much faster and less painful."