Shoaling Behavior in the Central Mudminnow (Umbra limi)

The central mudminnow (Umbra limi Kirtland, 1841) is a small freshwater fish that inhabits slow-moving waters in central North America. In this study, we investigate shoaling behavior in the central mudminnow. In Experiment 1, a focal mudminnow was given the simultaneous choice to spend time near an adjacent aquarium with five conspecifics or near an empty aquarium. Mudminnows (n = 22) clearly preferred to spend time near the aggregate of conspecifics, suggesting that mudminnows are a shoaling species. In Experiments 2 and 3, a focal mudminnow was given the simultaneous choice to spend time near an aquarium with a small shoal of conspecifics (n = 3 for both experiments) or near an aquarium with a larger shoal of conspecifics (n = 7 for Experiment 2; n = 12 for Experiment 3). In these experiments mudminnows (n = 22 for Experiments 2 and 3) hovered near both small and large shoals, but did not prefer to spend time near one shoal over the other. Together, these experiments suggest that mudminnow shoaling decisions are not influenced by shoal size, at least under the conditions of these experiments. Our investigation begins to define social behavior in this relatively common but rarely studied species.