Fish Can Count to Four

Khemist writes "Fish can count, according to scientists, who have found that North American mosquito fish have the ability to count up to four. Previously it was known that fish could tell big shoals from small ones, but researchers have now found that they have a limited ability to count how many other fish are nearby. This means that they have similar counting abilities to those observed in apes, monkeys and dolphins and humans with very limited mathematical ability."

Clever Hans

[suso]

Have they ruled out the Clever Hans [wikipedia.org] effect? Doesn't look like it.

Re:so off the mark

[Anonymous Coward]

I think you're misunderstanding the article. They ARE testing instinctive behaviour. Nobody is claiming that these fish are deliberately making any conscious decisions, or that they understand why they're choosing one group over another. The term "counting" might be misleading you, as it does imply intelligent thought, but in this case they simply mean that they can tell the difference between 3 and 4, in certain situations. They probably shouldn't use the word "count", but it's easier to explain to the average joe that way, plus, of course, it sounds more impressive. I'm willing to bet the biologists never actually use the word "count" in their paper. You do have a valid question, in that we don't know if all the fish involved were of comparable size, or if that was even taken in to account. Perhaps a shoal of 3 gravid females would appeal more than a shoal of 4 scrawny young fish, but the article doesn't go into that much detail about the methods used and whether that was considered. However, you are incorrect to assume that the physical size or mass of the shoal is all that is determining the response, and for the same reason that you're right to point out that the size of the individual fish may matter... we don't have enough details about the experiments to understand that. They may have measured that, and they may not have. Even if you're right and they'd prefer a group of 3 large fish over 4 small fish, that still indicates that they are able to compare two groups and determine which one is bigger, they just would be "counting" a different factor... overall mass versus individual numbers. From a biological standpoint, it would be just as significant. Furthermore, the most interesting bit of the study is how the mosquito fish compare to other animals known to be able to discern between small numbers. It suggests that there's a fundamental mechanism for visually estimating size or quantity that's common to a wide range of animals, whether due to an ancient evolutionary origin or from multiple developments of a similar function. Which further suggests that, from an evolutionary standpoint, there's a benefit to knowing the difference between one, two, three, and four, but not as much benefit to being able to tell 10 apart from 14.

Also... unless you've been giving money to Italian universities lately, it's silly to complain about your tax dollars being wasted on this. :-)