Fish smarts

A pufferfish. harum.koh, CC BY-SA 2.0 (adjusted, cropped).

Recently scientists have discovered that fish are actually very smart and can be favorably compared to some non-human primates. The problem in the past was that there was a dearth of information about their behavior and social lives, so many of our ideas about fish came more from intuition than evidence.

So if fish are not chowderheaded automatons operating solely on instinct, then how smart are they?

Comparing intelligence between different types of animals is difficult because they are different. Their environments, priorities, and abilities can vary significantly. Normally we measure human intelligence by asking questions about common knowledge mixed with some specialized knowledge and perhaps some algebra. This doesn’t work well with other cultures and especially not with other animals. With animals we have to look at the basics, like their ability to solve puzzles, and then we compare that with other animals. Doing this with fish has prompted a number of researchers to say that fish compare favorably in some tasks with primates, such as monkeys, which is quite surprising.

Most of the tests have so far only been done with specific species, so our assessments are limited and don’t apply to all fish. There’s bound to be considerable variation between the many different species, just as each species’ abilities will vary between the types of tests. For example, some freshwater fish—galaxias and wild rainbow trout—can learn certain tasks faster than rats. So are they more comparable to rats or monkeys? Well, it depends on what you ask them to do. Pigeons are better than people at spotting someone lost in the open ocean while searching from a helicopter, and at recognizing the shadows of cancer on an X-ray, even though their brains are only the size of a marble. It also depends on what species you’re comparing, and on the animals’ individual personalities, since some individuals in a species will be better at some things than others.

When Israeli researchers studying navigation in fish taught six goldfish to drive a fishmobile—a fish tank on wheels—using their orientation and movements. Two of the goldfish learned faster than others, but all of them soon became particularly good at avoiding obstacles to reach their target, and when allowed to roam freely, one of them took off down a corridor exploring the building.

It’s the differences between individuals that, in fact, define an individual’s personality. Whether they’re shy or bold, aggressive or passive, these are personality traits, and such differences can even be found in bacteria. Personalities do have an effect on intelligence and some individuals are smarter than others within their species and some species are more intelligent than others.

Many people think fish have poor memories or no memory at all, but this is completely wrong. We know that all creatures have some form of memory, including plants and microbes.

An international group of scientists in Texas found that bacteria not only remember things, they’re able to pass this information on to their offspring and then on to theirs for a minimum of four generations. This information tells their descendants whether they should remain in their environment or try to find someplace better to live, which is important since the one they studied splits in half every half hour or so. Even round worms remember things for at least a couple of hours.

But if we find memory in the tiniest of organisms, then it would be a huge surprise if we didn’t find it in fish. And, not to worry, fish do have very good memories.

Fish can remember things for at least a year—the amount of time studied, and for some fish their normal lifespan—and likely much longer depending on the type of fish. A shark, no doubt remembers things far longer than a minnow simply because they live a lot longer. The false idea that fish have a three-second memory stems from long-discredited hypothesis that a fish’s attention span is just a few seconds—that they live totally in the present—but we now know they do remember the past and anticipate the future, just like we do. It’s actually very easy to train fish. Unfortunately people still accept this falsehood without giving it any thought, and they’ve used that lie to justify things that are very harmful to fish.

Their long-term memories can be as good as most other animals, including some people. Here’s one rather impressive example.

Fish that live in tide pools are confined to small pools at low tide. If they discover there’s a predator, like an octopus, hiding in there with them, they need a way to make a rapid escape, so what gobies and other tide pool fish do is, when the tide is high, they memorize a three-dimensional map of the rocky shore’s topography, taking into account where the waterline will be at low tide.

Then when they find themselves in a difficult situation, they blindly leap into the air to land in the next pool, which they’re no longer able to see. They go solely by memory. If they miss, they might be able to flop around until they get in the pool without a hungry bird or crab noticing them, or they might dry up in the sun. A mistake can easily kill them. It’s a dangerous maneuver, but one that could save their life under dire circumstances.

We can make similar cognitive maps, as do many other animals. In the case of fish, it requires planning for the future, while also predicting the water levels at various times and places, but they are very good at it. Fish that were tested were successful ninety-seven percent of the time, while fish who weren’t given a chance to study the terrain made it only fifteen percent of the time. And interestingly, forty days later the knowledgeable fish still recalled their terrain maps and made successful escapes without a refresher course.

There are several types of memory and a number of ways memories can form and be retained, from iron levels in bacteria to RNA in slugs to neuron synapse connections in us, not to suggest that we don’t use all three and many others.

Fish learn from their experiences, of course, but they are very social, so much of their knowledge is gained by watching others or even from watching videos of other fish. They can also use this third-party perspective of watching others to quickly figure out their own place in the hierarchy. In addition, they’re very conscious of who’s watching them. For some fish, if two males are fighting, they’re more aggressive if other males are looking on, since it will increase their status, but they’re less aggressive when females are around when the females see aggression as less desirable in a potential mate.

Here’s a simple experiment involving time, observation, attention, and memory. When presented with a red and a blue plate of identical food, if you start eating from the red plate, the blue one is taken away. If you start with the blue plate, the red one remains there for you to eat later. With no instructions, we’d probably figure out what’s going on after just a few trials, since we’re familiar with tests and experiments, but animals wouldn’t expect such deviousness so it takes them longer.

Cleaner wrasses establish cleaning stations to groom other fish. Here black-and-white-stripped cleaner wrasses tend to two yellow-saddle goatfish. Which of these two species do you think might be smarter: the big one or the smaller one? Silke Baron, CC BY 2.0 (adjusted).

Scientists ran this experiment on orangutans, chimpanzees, capuchin monkeys, and cleaner wrasses. Unfortunately they didn’t include high-school students. All of the cleaner wrasses figured it out the fastest. Two of the chimps caught on soon after, but the rest didn’t. After modifying the test to make it easier, the rest eventually figured it out, except for the other two chimps who never got it. We don’t know how well the high-school students would have done, but one researcher tested his four-year-old daughter and she never caught on.

The researchers then swapped the plate colors so if you start with the blue plate, the red one is taken away, but only the fish and capuchins sussed the change within a hundred trials. On the other hand, while it’s not obvious, the test was designed to fit the sorts of decisions cleaner fish have to make on a regular basis, since they have to judge whether a client fish will hang around or swim away. Their regulars will be patient and more likely to wait their turn, while newbies might just take off.

Of course, primates are smart and inventive problem solvers, but they seemed to get frustrated with this task and may have just given up on it until the key suddenly occurred to them.

 

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