Zebrafish excel in number discrimination under an operant conditioning paradigm

Area of Science:

• Comparative cognition
• Animal behavior
• Neuroethology

Background:

• Numerical discrimination is observed across vertebrates but varies significantly between species.
• The guppy (Poecilia reticulata) shows advanced numerical skills among teleosts, raising questions about whether this is species-specific or common to teleosts.

Purpose of the Study:

• To investigate the numerical discrimination abilities of zebrafish (Danio rerio).
• To compare zebrafish numerosity skills with those of other vertebrate species, including guppies.

Main Methods:

• Zebrafish were trained to differentiate numerosities with a difference of one item, from 2 vs. 3 to 5 vs. 6.
• Non-numerical variables (density, area) were controlled to ensure discrimination was based on number.
• A control group was trained to discriminate shapes to assess learning rates and strategies.

Main Results:

• Zebrafish successfully discriminated numbers up to 4 vs. 5, with no sex differences in accuracy.
• While no individual mastered the 5 vs. 6 task, group performance was significant, indicating a potential discrimination threshold.
• Zebrafish showed comparable numerosity skills to guppies, exceeding those of dogs, horses, and fowl, but below parrots, corvids, and primates.
• Zebrafish were slightly more accurate with area discrimination than numerical discrimination, and males outperformed females in area tasks.
• Both number-trained and area-trained fish generalized their learning to the other stimulus type, suggesting a relational strategy.

Conclusions:

• Zebrafish possess significant numerical discrimination abilities, comparable to guppies and surpassing several warm-blooded vertebrates.
• These findings suggest that advanced numerical cognition may be more widespread among teleosts than previously thought.
• Zebrafish employ relational strategies for discrimination tasks, generalizing learning between numerosities and areas.