Fish can distinguish between larger and smaller quantities, with an additional ability to "count" up to three, according to research on tropical angelfish.
Angelfish are regarded as being one of the world's most intelligent fish, but scientists believe other fish species also possess the math-related skills outlined in a new Animal Cognition paper.
Doing something akin to counting up to three might sound underwhelming, but math itself is a very human-centric concept that may need reconsideration if comparisons are to be made with the abilities of non-human species.
"We all think we know what we mean by 'counting,' but do we really?" asked co-author Robert Gerlai. "Is recounting a series of 1 to 100 counting? Is 2+3=5 counting? Is calculating the square root of a number counting, or perhaps is the mathematics necessary for quantum physics counting?"
"The point is that even within our own species, mathematical abilities vary tremendously," Gerlai, a University of Toronto Mississauga professor of psychology, told Discovery News. "So far, most biological, including behavioral, traits we initially believed to be unique properties of our own species have turned out to have some homologues in animals."
Gerlai and Luis Gomez-Laplaza of the University of Oviedo in Spain exploited the previously determined tendency of angelfish to seek protection in unfamiliar environments by joining the largest possible fish group, called a shoal. To rule out possible confounding effects arising from sexual interactions, the researchers only used juvenile angelfish for their experiments.
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Test fish placed in special compartmentalized tanks were given a simultaneous choice between shoals containing different numbers of fish. The angelfish were always able to select the larger of two groups so long as the ratio between the shoals was 2:1 or above. Below that ratio, their choices were less predictable, suggesting a limit to their quantity estimation abilities.
After the findings were published, the researchers, according to Gerlai, "have already collected new data suggesting that angelfish can discriminate much more precisely than this. That is, angelfish can tell the difference between 3 and 2, for example."
He added, "This ability does resemble 'counting' individual items as opposed to estimating quantities, but this counting ability does not extend beyond three."
Precise counting ability likely does not benefit fish much, so they have probably not evolved skills beyond those detected by the scientists. Estimating group sizes, however, allows the fish to enjoy better protection in larger groups and improved food detection, with more eyes on the lookout for food sources. The ability to choose between larger and smaller quantities, therefore, has survival value for fish.
Angelo Bisazza, a professor in the Comparative Psychology Research Group at the University of Padova, has performed studies on mosquitofish suggesting that they too have quantity estimation skills. Bisazza and his team were even able to train the mosquitofish to discriminate between more difficult to detect ratios.
Bisazza told Discovery News that the studies "are slowly unraveling the cognitive abilities of fish and, as for the case of numerical abilities, they often suggest that the capabilities of these creatures are not so dissimilar from those of the organisms (monkeys, rodents and pigeons) that have traditionally been employed for these studies."
Nicola Clayton, a leading animal cognition expert at the University of Cambridge, told Discovery News that the research is reminiscent of studies on lions and salamanders, and how these animals can also estimate quantity. She additionally predicts that other species of fish that live in shoals have the ability.
Given how widespread the basic math-related skills are throughout the animal kingdom, Gerlai thinks it's possible that ability to count "could have arisen in one ancestral species from which all species with this ability evolved." Alternatively, he said the skill "could have arisen independently in several species."
In the future, studies on genes could provide the answers, Gerlai predicts. Discovery of a gene or sets of genes that underlie counting, estimation, and other math skills could be traced across multiple species.
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