Little is known on cognitive abilities in fish. Recent studies provided evidence for the processes underlying discrimination of small quantities. In the present paper, the authors studied the discrimination of “large numerosities”. Using social reinforcement in mosquitofish, in an original set of experiments, they show that fish are able to use pure numerical information when discriminating large numbers (above four), thus extending the data of a previous paper published in PlosOne in 2009. The present data confirm the analytical ability of fish in spatial discriminations, an ability similar to the one of mammals. Interestingly, tests undertaken, in a similar situation, on undergraduate students “essentially replicated the results previously obtained with fish”.