Of the larvae given the choice of walls with one or four bars, 66.5 percent preferred the wall with four bars. Moreover, in tests that also took into account the thickness and distribution of the rods to exclude other stimuli, more than 63 percent of the larvae preferred walls with a higher number of rods. The researchers concluded that zebrafish larvae have a sense of numbers and prefer large numbers.
The researchers note that the challenge in studies of numerical cognition is determining whether the animal is using real numerical information or is relying on the non-numerical physical properties of a stimulus. Demonstrating numerical ability requires a series of carefully controlled experiments that prevent access to non-numeric information. This has been done adequately with a number of well-established control conditions.
Previous research has shown numerical abilities in newborn babies, as well as newly hatched guppies and chicks – species whose brains are already developed at birth. However, prior to this study, there was only sparse knowledge of the numerical abilities of non-human species born with underdeveloped brains. “Confirmation of our hypothesis certainly requires more data on zebrafish larvae based on various stimuli such as horizontal bars and other objects as well as tests that exploit other numerical behaviours,” the research team wrote in their conclusion.
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