Abstract: Knowledge of factors limiting fish dispersal requires knowledge of fish swimming ability. But the abilities of most fish species are unknown. Darters (subfamily Etheostomatinae) are particularly understudied, and knowledge of their swimming abilities is valuable for multiple reasons. With around 250 described species, darters represent a significant portion of North American freshwater fish diversity. Many darter species are benthic specialists with restricted movement and are therefore particularly susceptible to habitat fragmentation. To help fill this knowledge gap, our goal was to model swimming speeds across a diversity of darter species. Specifically, we used a swim-tunnel to measure the critical swimming speeds (Ucrit) of nine darter species, and we modeled the effects of various morphological characteristics on the Ucrit estimates. Mean Ucrit by species ranged from 58.98 to 133.01 cm/s. A one-way ANCOVA indicated that darter Ucrit was affected by species identity (p = 0.046) and total length (p = 0.002). A Tukey’s test identified that Greenside Darters swam significantly faster than Christmas Darters, Coosa Darters, Fantail Darters, Redline Darters, and Turquoise Darters (p < 0.05 for all comparisons). Our results demonstrate that darter swimming speed can be generalizable, but this generalization has limits. All species with significantly different swimming speeds had significantly different total lengths, with the larger of the pair (i.e., Greenside Darters) swimming faster. However, there were several species pairs with significantly different lengths but similar swimming speeds. Preliminary results suggest that including more functional trait information may provide a better understanding of Ucrit. For example, Greenside Darters tended to have a larger relative distance between the dorsal and ventral insertions of the pectoral fins than did significantly slower species. A broader pectoral fin base may allow individuals to hold against greater flows. Various other functional traits may affect swimming abilities as well. Results of our continuing research will be valuable to basic ecologists concerned with factors affecting fish swimming and dispersal abilities. Our results will also be useful to applied ecologists concerned with effects of instream structures and altered instream flows on darter movement.
