Numerical discrimination in Danionella

The transparent teleost Danionella cerebrum offers unique advantages for neuroscience research, including small size, lifelong cranial transparency, and a simplified brain. Despite its suitability for imaging and neural circuit studies, its cognitive abilities remain largely unexplored. Here, we show that Danionella can discriminate between quantities. Using a habituation/dishabituation paradigm over six trials across five days, fish were exposed to dot arrays of constant numerosity (e.g., 3 dots), while geometric visual properties were systematically varied to ensure responses were driven by actual numerical information. In the final trial, a different numerosity (e.g., 9 dots) was presented. Fish showed significant dishabituation, spending more time near the numerically altered stimulus, indicating discrimination between 3 and 9 elements. These findings contribute to our understanding of Danionella's cognitive capacities and support its broader use in research, particularly for investigating the neural basis of cognition at high resolution, given its exceptional biological features.