Polyculture of Endangered Bonytails and Razorback Suckers in Recirculated Water

Abstract

Bonytails 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 × 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 as the number of required siphoning events per replicate (432‐L tank), was significantly lower 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.

Endangered species managing endangered species: Polyculture of piscivorous Colorado Pikeminnow (Ptychocheilus lucius) with production Bonytail (Gila elegans) to control recruitment and increase growth rates

“…Optimizing growth rates has been a specific recovery objective for Bonytail in the lower Colorado River because conservation goals associated with augmentation require a minimum stocking size in an effort to increase post‐release survival (Bureau of Reclamation, ; Lower Colorado River Multi‐Species Conservation Program, ). Although several studies have evaluated aquaculture techniques (i.e., cage culture, diet improvement, polyculture and thermal regimes) to facilitate Bonytail growth (Henne et al, ; Kappenman et al, ; Sowka & Brunkow, ), the effect of uncontrolled recruitment on growth rates of production fish has not been evaluated. The use of biological controls has been shown to greatly reduce densities (Kavanagh & Olson, ; Ward & Slaney, ; Ward et al, ; Westers, ), and, indeed, our results demonstrated Colorado Pikeminnow to be effective at reducing total biomass.…”

“…Although several studies have evaluated aquaculture techniques (i.e., cage culture, diet improvement, polyculture and thermal regimes) to facilitate Bonytail growth (Henne et al, 2007(Henne et al, , 2006Kappenman et al, 2012;Sowka & Brunkow, 1999), the effect of uncontrolled recruitment on growth rates of production fish has not been evaluated. The use of biological controls has been shown to greatly reduce densities (Kavanagh & Olson, 2014;Ward & Slaney, 1988;Ward et al, 1989;Westers, 2001), We observed a positive effect of initial size in both the ∆TL and ∆g models, indicating the starting sizes of fish had a strong effect on their growth over time.…”

“…Uncontrolled recruitment, and subsequent high densities, can have negative impacts on captive production including increased mortality pre-and post-release, decreased growth rates and reduced physiological condition (Kavanagh & Olson, 2014;Ward & Slaney, 1988;Ward, Slaney, Facchin, & Land, 1989;Westers, 2001). In addition, high densities often foster poor water quality and increase susceptibility to disease (Henne, Romero, & Carmichael, 2007;Westers, 2001). These negative impacts could have severe management implications pertaining to the conservation of Bonytail.…”

When more is more: taking advantage of species diversity to move towards sustainable aquaculture

“…This species compatibility is either intrinsic or is ensured by management practices (Table 2). An example of intrinsic compatibility is the polyculture of benthic and pelagic species, which minimises interspecific competition (Henne et al ., 2007; Kozlowski et al ., 2014). Ad libitum feeding, which avoids interspecific competition in the farmed stock (Sonay & Bascinar, 2017) is an example of a management practice that promotes compatibility.…”

“…Use of the benthic behaviour of X. texanus. Consumption and resuspension of solid waste in the water column, which helps it leave the system instead of accumulating on the bottom of the basin Henne, Romero & Carmichael (2007) Pikeperch (Sander lucioperca) and sterlet (Acipenser ruthenus) reared in a RAS…”