“You Have the Memory of a Fish” Is Sort of a Compliment

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Slate’s animal blog.
July 1 2014 7:00 PM

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For those of you who are teased about your forgetfulness, good news! It turns out having the “memory of a fish” may actually be a compliment. Fish may have a reputation for having three-second memories, but new research suggests that we’ve been underestimating their abilities. In a study presented today at the annual meeting of the Society for Experimental Biology, researchers from MacEwan University in Canada found that African cichlids have a memory span of at least 12 days.

African cichlids are common aquarium pets, and there are lots of anecdotal reports from their owners about their intelligence. Some people claim that cichlids greet them when they come home; others believe their cichlids watch TV with them. According to psychologist Trevor Hamilton, some even claim cichlids process what they’re watching: “If there’s something scary, they’ll react with a fearful response.”

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The jury is still out on cichlids’ TV watching habits, but scientists have come up with more empirical methods of assessing cichlid intelligence. Memory is an especially important skill to have; for animals in the wild, remembering good places to find food can mean a long life and evolutionary success.

To assess cichlids’ memory for food sources, Hamilton, along with undergraduate Erica Ingraham and psychologist Nicole Anderson, tested seven fish. Each fish was placed individually in a tank. The sides of the tank were outfitted with screens that showed a striped black and white display. In one area of the tank, the stripes on the screen looked like they were moving upward; in the other area, they looked like they were moving down. When fish were in the area with upward-moving lines, they were fed. The researchers trained the fish for three 5-minute sessions over a five-day period.

Eleven days after the last training session, they let the fish go hungry so that they would have increased motivation to seek out food. On the 12th day, they brought fish back to the tank one at a time and took note of where they hung out. Six of the seven fish they tested spent more time in the area with upward-moving lines, suggesting that they remembered they had gotten food there previously and were hoping to find it there again.

To eliminate the possibility that fish just have a natural preference for upward-moving designs, Ingraham, Anderson, and Hamilton repeated this study by training the same cichlids to associate food with the other area of the tank, the one with downward-moving lines. The cichlids succeeded at remembering that, too. Not only can these fish learn an association and remember it for 12 days; they can learn something new that overrides their old knowledge and remember that for 12 days, too.

Hamilton notes that we still have much to learn about cichlid memory. Cichlids in this study were able to remember for 12 days where they had found food, but that “doesn’t mean that’s the maximum or minimum,” Hamilton says.

Now these researchers want to explore other claims about cichlid intelligence. “We’re looking at their ability to identify different perceptual stimuli in terms of pattern recognition,” says Hamilton. It is yet to be seen whether cichlids can identify patterns more complicated than moving stripes, such as their owner’s face. Fish owners, there may be more going on in your aquarium than you thought.

Jane C. Hu has a Ph.D. in psychology from the University of California–Berkeley and is a 2014 AAAS Mass Media Fellow. Follow her on Twitter.

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