Polyculture of endangered bonytails and razorback suckers in recirculated water

Bonytaits Gila elegans and razorback suckers Xyrauchen texanus are imperiled fish species that are endemic to the Colorado River system in the southwestern United States. Captive propagation is a component of the recovery plan for each species, which are sometimes cultured together indoors in water reuse systems. A 3 X 2 factorial design was selected for examining the co-culture of two bonytail size-classes with razorback suckers at three densities (0, 2, or 5 razorback suckers/tank) for 120 d. There were four replicates of the design. Tank cleaning effort, measured,is the number of required siphoning events per replicate (432-L tank), was significantly tower in tanks containing razorback suckers and bonytails (polyculture) relative to those without razorback suckers (monoculture). Survival was high, averaging 100% for razorback suckers and 96% for bonytails, but bonytail survival was significantly (P < 0.05) lower for small bonytails cultured with 2 razorback suckers/tank relative to all other treatments. Razorback sucker density did not significantly affect the relative growth rate, specific growth rate, or final size (total length and weight) of either bonytail size-class but did result in significantly greater growth rates and final weight for razorback suckers at 2 fish/tank than at 5 fish/tank. Relative and specific growth rates were significantly greater for small bonytails (0.90% and 0.59%, respectively) than for large bonytails (0.31% and 0.26%, respectively). Bonytail size did not significantly affect razorback sucker growth rate or final size. Polyculture of these two fishes can increase culture efficiency and reduce the need for siphoning waste from culture tanks, a labor-intensive practice that is potentially stressful to the fish. Co-culture of bonytails and razorback suckers in recirculated water is a beneficial husbandry practice available to resource managers.