Use of number by fish.

Area of Science:

• Comparative Cognition
• Animal Behavior
• Neuroethology

Background:

• Rudimentary numerical abilities exist in various species before language evolution.
• Debate continues on whether animals use true numerical representation or perceptual cues.
• Mental number representation is well-documented in few mammals.

Purpose of the Study:

• To investigate if mosquitofish can learn quantity discrimination (2 vs. 3 objects).
• To determine if mosquitofish can discriminate quantities without non-numerical perceptual variables.
• To provide evidence for numerical representation in fish.

Main Methods:

• Mosquitofish were trained to differentiate sets of geometric figures varying in quantity.
• Experiments controlled for non-numerical variables like shape, size, brightness, and distance.
• Performance was assessed when non-numerical cues (cumulative surface area, space occupied) were matched.

Main Results:

• Mosquitofish used cumulative surface area and space occupied as cues in initial discrimination tasks.
• When these non-numerical cues were controlled, fish still learned to discriminate quantities.
• Discrimination performance was comparable whether non-numerical cues were available or not.

Conclusions:

• Mosquitofish demonstrate the ability to discriminate small quantities independent of non-numerical cues.
• This study offers the first evidence of numerical abilities in fish, akin to primates.
• Numerical discrimination in fish, like in primates, appears to be a 'last resort' strategy.