Wesp, H.M.*; Gibb, A.C.: Escape Response Performance in the Larval Razorback Sucker, Xyrauchen texanus

The razorback sucker, Xyrauchen texanus, is an endangered fish native to the Colorado River system. Previous research suggests that declines in wild populations are due to a lack of larval recruitment. In this study, we tested the hypothesis that poor escape response performance of larval razorback suckers contributes to low recruitment. The larval escape response behaviors of razorback suckers reared at 12^* C and 18^* C were elicited and digitally recorded over a developmental period to determine 1) if the larvae displayed the escape response and 2) if maximum swimming speed during the response was significantly slower than speeds reported for other fish larva. Response behaviors for 56 razorback suckers were digitized using Didge analysis software. Larval razorback suckers did display escape response behaviors, with speed of the response increasing as length increased during development. In addition, escape response speeds for suckers were similar to those reported for other fish larva at the same size. Preliminary temperature comparisons indicate that maximum swimming speed during the escape shows a Q₁₀ relationship of approximately 0.2. This low value suggests that the colder water temperature does not significantly affect escape response behavior. Thus, it appears that razorback suckers are capable of acclimating to lower Colorado River temperatures and poor escape response performance does not contribute to the lack of recruitment in the wild. Future work will compare escape response performance between the native razorback sucker and an introduced species, the rainbow trout, Oncorhynchus mykiss.