Do fish count? Spontaneous discrimination of quantity in female mosquitofish
The spontaneous tendency to join the largest social group was used to investigate quantity discrimination in fish. Fish discriminated between shoals that differed by one element when the paired numbers were 1vs2, 2vs3 and 3vs4, but not when 4vs5 or larger. Using large numerosities (>4), the ability to discriminate between two numbers improved as the numerical distance between them increased and a significant discrimination was found only with ratios of 1:2 or smaller (4vs8, 8vs16 and 4vs10). Experiments to control for non-numerical variables evidenced the role played by the total area of stimuli with both large and small numerosities; the total quantity of movement of the fish within a shoal appeared also important but only when large numerosities were involved. Even though the pattern of discrimination exhibited by female mosquitofish is not fully consistent with any of the existing models of quantity representation, our results seem to suggest two distinct mechanisms in fish, one used to compare small numbers of objects and one used when larger numerosities are involved.
KeywordsFish cognition Quantity discrimination Continuous variable Number
- Hauser MD, Spelke ES (2004) Evolutionary and developmental foundations of human knowledge: a case study of mathematics. In: Gazzaniga M (ed) The cognitive neurosciences, vol 3. MIT Press, CambridgeGoogle Scholar
- Reynolds WW, Casterlin ME (1979) Effect of temperature on locomotor activity in the goldfish (Carassius auratus) and the bluegill (Lepomis macrochirus): presence of an ‘activity well’ in the region of the final preferendum. Hydrobiologia 65(1):3–5Google Scholar
- Rohlf FJ (2004) TPSDIG, Version 1.40. Dept. of Ecology and Evolution, State Univ. of New York, Stony BrookGoogle Scholar
- Sokal RR, Rohlf FJ (1995) Biometry. Freeman and Company, New YorkGoogle Scholar