Can Fish Count? - Numberphile

it turns out and there's a now quite a history of this uh relatively recently uh people have found that there are a lot of species who can do uh number tasks by number tasks I mean tasks which depend upon uh understanding the number of objects in a display or what we would call numerosity so you have to be very careful here because um you can't talk to other species and they can't talk to you uh so you can't explain to them what aspects of the stimulus you want them to respond to but you but you have to design the the the stimuli rather carefully so that the critical aspect of the stimuli is the numerosity of objects actually before the second world war a a brilliant German ethologist called Otto kler had shown that corvids crows Jack doors and so on had quite a good number sense that they could match to sample numbers up to about seven so he'd show them a sample of black blobs and then they had to select one of a two or three objects which had the same number of blobs blobs would be arranged differently if they got it right they got rewarded if they got it wrong they didn't and they were pretty good at this these corvids since then there was a I mean since the the 30s there's been a kind of a a Hiatus in research on on animal numerical cognition but in since the '90s it's really started to take off again and we now know that the whole range of different animals can can do this both in the wild and in Laboratories particularly in Laboratories we were interested in the counting abilities of fish now small fish often swim in shes and if they are in a sh there's a smaller risk of predation than if they're by themselves and if they're in a bigger show they've got a smaller risk of predation than if they're in a smaller shoulder safety and numbers safety and numbers exactly so you can use this natural behavior of uh of these small fish and test it in the laboratory so you can put them in a a transparent tank with a few fish on this side and a few more fish on the other side and you see which side they they swim to it's been shown not by me uh but by my collaborators that they will swim to the sh of the side of the of the tank with more fish in it what we were interested to do in in a paper we published this year was to see whether they had a difference between small number uh perception and large number perception so in humans what happens is that if you have to compare four versus 3 four versus 2 four versus 1 3 versus 2 this is all equally easy it doesn't depend on the ratio of one number to the other so four against one is just as easy as four against three however once you get uh larger numbers let's say 8 against s or 8 against 5 then there's a ratio effect that is the bigger the difference between those two numbers the easier it is the question is would this be true of Guppies which were a small fish about that big relatively small brain and the answer was yes that these small fish didn't show a ratio effect when we you ask them to compare four versus one compared to four versus three but for larger numbers they did show a ratio effect which suggests that like us they have these two systems small number system and a larger number system and we thought this was really quite an intriguing result I can imagine someone at home thinking well surely the fish just looks at two different groups of fish or shs of fish and can just measure which one's bigger which one takes up more volume and swims towards that and it hasn't used any number sense there it's just used an understanding of how big something is how was the experiments that you've been involved with getting around that well it's very difficult to control because not only uh there more fish over here they're of course swimming around and you could have fewer fish over there and they're swimming around so uh it's really quite difficult for the the the subject fish to be able to make an estimate but even though they do it actually rather well how do we know that they're enumerating the fish this side versus that side well there are ways in which you can manipulate uh the amount of fishness on this side the amount of fishness on that side for example by putting slightly larger fish on this side to balance the number of fish on that side that creates some problems um because of fish psychology which I'm not an expert in uh like uh some fish prefer to swim in shs with larger fish um and so you know that creates complications however my my collaborators have done a nice training experiment uh in which the the fish doesn't have to choose between two shs it has to select a gate into another tank to join its friends and above the gate will be uh a number of blobs and the fish has to choose the right number of blobs it would have had a training session in which a certain number of blobs would be rewarded and a different number of blobs would not let's say three is rewarded two is not rewarded in the test there' be different blobs but there'll be threeness and Tess so but different Arrangements of threeness and Tess and the fish can learn this actually can learn it quite well so there's now quite good evidence that the Fisher can respond to to to number but of course they might also in in the wild be responding to other cues like the amount of fishiness uh in the in the neighborhood and of course these are typically correlated with the number um so um you you want to try and tease them apart experimentally but in in real life of course they they uh they tend to go together how does understanding the mathematical cognition or the number cognition of Guppies help anything why why why have you got an interest in this well we want to know what kinds of capacities uh the uh the human brain inherits