From learning to reversal learning: How non-cleaner fish tackle the biological market task.

The biological market task – also known as the ephemeral reward task – models the mutualistic cleaning interactions between bluestreak cleaner wrasses and their client fish on coral reefs. In this dichotomous choice paradigm, selecting an “ephemeral” food option first grants access to a “permanent” food option, while choosing the permanent option first makes the ephemeral one unavailable. Cleaner fish have previously outperformed other vertebrates on this task, presumably because the cues to solve it are more ecologically salient for cleaner fish. In this study, we tested whether this advantage extends to non-cleaner fish by assessing the learning and reversal learning performance of three dottyback species (Pseudochromis spp.) – mesopredator reef fish that do not engage in cleaning mutualisms – on the original task and two derived versions that varied in the cue required for solving it. Dottybacks performed poorly in all versions of the task. Notably, they did worse in the original task than cleaner wrasses tested previously, suggesting that cleaner fish’ success is tied to specific ecological conditions not shared by other species. Further analyses revealed subtle differences in performance between tasks and faster learning in the initial test compared to the reversal test, an indicator of limited cognitive flexibility. Together, these findings help fill a gap in the biological market literature and underscore how species-specific ecological traits and task structure shape cognitive performance.