Evaluation of Rearing Razorback Suckers (Xyrauchen texanus) in Flowing Raceways at Lake Mead Fish Hatchery

Authors: Brandon L. Senger, Jon C. Sjoberg

Year: 2010 (xlii)

Abstract

Razorback suckers (Xyrauchen texanus) are currently being raised in several hatcheries and are used for repatriation programs throughout the lower Colorado River basin. However, hatchery reared razorback suckers have shown poor post stocking survivability. Repatriated razorback suckers readily succumb to predation by nonnative fishes after being released into the wild. Increasing the target size of stocked fish has been the standard method to deter and prevent predation by gape limited predators. Recent research began investigating alternative rearing methods, via captive enrichment, that would increase overall fitness and condition of hatchery reared razorback suckers, ultimately leading to wild recruitment. The purpose of this study is to design and construct experimental raceways to evaluate rearing protocols of razorback suckers in flowing conditions. We compared swimming stamina, growth, food conversion efficiency, foraging ability, and disease treatment of fish reared in standing water, fish reared in a low and variable velocity raceway, and fish reared in a high velocity raceway to test the effects of exercise and flow conditioning on hatchery reared razorback suckers. Swimming performance, growth, and food conversion efficiency were highest among fish exposed to flowing water conditions. Furthermore, fish in the highest velocity treatment performed better in each category tested. The unexercised fish in the standing water raceway exhibited the lowest results during testing. We not only wanted to evaluate the physiological benefits from flow conditioning and exercise, but also the practicality of rearing fish at hatcheries in flowing raceways. Our results indicate that fish benefited the most from the design of the high velocity treatment. In addition to higher growth and swimming stamina, fish in the high velocity raceway had a more efficient food conversion rate. There is still limited information available on how captive enrichment aids in increasing post stocking survivability. These experimental results suggest that flow conditioned fish should have a higher overall fitness and that flow conditioning is a beneficial tool for captive rearing of razorback suckers. However, future studies need to be conducted on post release survivability of flow conditioned razorback suckers.