Data and code from: Color and shape cues differentially affect approach and choice behavior in peppermint shrimp (Lysmata wurdemanni)

Peppermint shrimp (Lysmata wurdemanni) are small benthic crustaceans that live on reefs of the western Atlantic, including the Gulf of Mexico, and are commonly kept in aquaria as cleaner shrimp, but their responses to visual cues have not been directly tested. We trained groups of captive L. wurdemanni over six weeks to associate specific colors and shapes with a food reward and recorded 375 behavioral observations across six experimental conditions. Among shrimp that approached, choice was above chance for both color targets (64–65%, p < 0.05) and shape targets (SRS: 72%, p < 0.001). Color and shape did not act the same way, however: color increased how often shrimp approached the feeding area, whereas once active, choice accuracy did not differ between color and shape conditions (Kruskal–Wallis: H = 1.15, p = 0.765). These results distinguish two parts of behavior: the decision to approach and the accuracy of choice once engaged. Color appeared to act mainly as a cue that prompts approach, while choice accuracy, once a shrimp was engaged, did not depend on whether the cue was color or shape. Because animals were housed in groups and individuals could not be reliably tracked, these patterns reflect group-level conditioned responses rather than demonstrated individual learning, and the higher approach under color is partly confounded with a procedural difference in cue presentation. We discuss possible roles for chemical cues in shape discrimination and for social dominance in group-based experiments.