"We have provided the first evidence that fish exhibit rudimentary mathematical abilities," the Telegraph quoted Agrillo as saying. He also revealed that his latest study was a follow-up to a previous study wherein he and his colleagues showed that, upon being harassed by a male fish, a female mosquito fish would try to avoid his attentions by seeking solace in the largest nearby shoal. That study demonstrated that the fish could differentiate between bigger shoals and smaller ones.
In their most recent research, the researchers conducted a series of experiments to see whether a lone mosquito fish would prefer to join a shoal of between two and four others.
They found that female fish preferred to join shoals that were larger by just one fish significantly more often- consistently preferring shoals of four fish rather than three fish, and consistently preferring shoals of three fish over those containing just two.
In another experiment, it was found that the fish were unable to directly count over four, though they could distinguish between larger numbers if they differed by a ratio of 2:1.
The results, published on the BBC Worldwide's natural history site, indicated that fish are able to visually estimate larger numbers, but not very accurately.
Lead researcher Professor Angelo Bisazza said that fishes' numerical abilities were similar to that of monkeys and human infants between six and 12 months old, who were both able to visually count small numbers and less accurately estimate larger ones.
"The most interesting thing is that fish performance is very similar to what is observed in adult humans who possess a very limited vocabulary for numbers," Dr Agrillo said.