Hatchery augmentation of dwindling wild populations has become a common strategy to avoid extinction of endangered fishes. While benign hatchery conditions can lead to low persistence of stocked individuals, experiments have demonstrated that flow conditioning of Razorback Sucker Xyrauchen texanus can increase swimming performance and reduce downstream movements from desired locations after stocking in the Colorado River basin, USA. However, managers have been slow to adopt its use, likely because linking experimental flow conditioning to scales that are relevant to conservation has been difficult. We reared age-2 Razorback Sucker in two raceways (control: n = 530; flow conditioning: n = 533) for 10 weeks to assess whether flow conditioning could increase apparent survival after stocking into the San Juan River, New Mexico. We used riverwide active sampling and remote PIT tag antennas to resample individuals for 3 years after stocking. Using Cormack-Jolly-Seber mark-recapture models, we assessed the effects of flow conditioning, size at stocking, relative condition (Fulton's K), and their interactions on apparent survival and downstream movement after stocking. Flow conditioning of fish doubled the mean apparent survival (at a mean size of 325 mm TL) during the first overwinter period (control fish: 0.14, 95% CI = 0.09-0.21; flow-conditioned fish: 0.28, 95% CI = 0.19-0.38), with both groups having similar mean overwinter apparent survival estimates thereafter (both > 0.75). Size at stocking and K were positively associated with first-overwinter apparent survival regardless of treatment (mean survival was <0.20 for fish <275 mm TL but was >0.65 for fish >450 mm TL). Downstream movement after stocking was negatively associated with fish size, indicating that emigration likely contributed to higher apparent mortality of smaller fish. Our results suggest that transitioning hatchery practices to include flow conditioning of Razorback Sucker (and potentially other endangered Colorado River fishes) prior to stocking could substantially increase the conservation efficiency of these augmentation programs.

Efforts to reintroduce razorback suckers Xyrauchen texanus to specific river reaches have been plagued by downstream drift and poor survival, which have been attributed to stress, disorientation, predation, and poor conditioning. Poststocking dispersal of eight test groups (15 fish each) of razorback suckers was examined for 28 d with telemetry equipment. Fish were released in three different locations in the Colorado River basin of Utah, Arizona, and Nevada: (1) a 65,000‐ha reservoir, (2) a small (<1‐ha) backwater, and (3) a large (30‐ha) backwater on the mainstem river. At each location, subgroups were released immediately (reference) or held to acclimate them to the site (3–7 d) before release. Two of four subgroups for the large‐backwater test were preconditioned to flow. Dispersal from the stocking sites was rapid and declined with time for all tests, as fish appeared to seek and find cover. Downstream drift was most pronounced (x = 69.5 km) from the small backwater and significantly (Kruskal–Wallis test, P < 0.01) greater than either the reservoir (x = 3.7 km) or large‐backwater sites (x = 7.7 km). Site‐acclimation tests were inconclusive, but downstream movement was significantly (Wilcoxon two‐sample test, Z = −2.298, P < 0.01) less for fish preconditioned to flow (x = 1.9 km) compared with pond‐reared fish (x = 7.7 km). We concluded that poststocking dispersal may decrease if razorback suckers are preconditioned to flow.

Captive propagation of the federally endangered Rio Grande silvery minnow Hybognathus amarus has been identified as essential for the recovery of the species. A starter diet was initially developed for this cyprinid to support rapid growth through the larval stage. The diet, however, was too costly to support the grower phase of the species. A series of trials was conducted to determine whether a grower diet could be developed that would be cost effective while maintaining fish performance. Quadruplicate lots of Rio Grande silvery minnow (approximately 90 d posthatch, 0.39-0.42 g) were fed a reference diet or one of five experimental diets until just before gonadal maturation at two facilities in New Mexico (New Mexico State University [NMSU] and Dexter National Fish Hatchery and Technology Center [Dexter]). The diets varied in percent composition of ingredients to account for a range in feed costs. Cyclop-eeze (Argent, Redmond, Washington), krill, liver, and fish meals were present in the reference diet and sequentially altered in the remaining test diets to maintain high protein levels in the diets (57.9-64.9% dry matter). Total weight gains at the end of the 16-week trials were lower than expected (140-200%), with no differences among diets at NMSU. Although total weight gain was less at Dexter (105-150%), there were differences among diets. Specific growth rate was greater at both facilities in fish fed the reference diet and a diet lowest in fish meal (1.82% per day). The highest growth rate occurred across all diets within the first 30 d of both feed trials and then diminished by the end of the trials. There were no detectable differences in critical swimming speed or fat scores in fish fed diets with and without expensive feed ingredients or increasing fish meal. The most consistent growth was observed when fish were fed a diet low in fish meal, and our results clearly identified a less-expensive grower formulation for the production of this imperiled cyprinid.

Captive propagation and augmentation of the Rio Grande Silvery Minnow Hybognathus amarus is necessary for continued persistence of the species until habitat can be restored. Augmentation occurs using captive fish within the first year (age 0) through age 2; however, older year‐classes (ages 3–4) have been released into the wild. We quantified fecundity and compared egg quality across four reproductive age‐classes (1–4) of hatchery‐reared Rio Grande Silvery Minnow. Batch fecundity (total number of spawned eggs) ranged from 2,029 eggs in age‐1 fish to 10,588 eggs in age‐4 fish. Standing stock of vitellogenic (i.e., yolked) oocytes remaining in ovaries after spawning increased from 988 oocytes at age 1 to 4,924 oocytes at age 4. Total fecundity (i.e., batch fecundity plus standing stock of yolked oocytes) increased from 3,017 eggs and yolked oocytes in age‐1 fish to 15,522 eggs and yolked oocytes in age‐4 fish. Of note, batch fecundity ranged from 57% to 68% across the four age‐classes indicating that over half of the total fecundity occurs in the first spawn. Average percent fertilization of eggs (63–82%) was not detectably different across the four age‐classes, while average egg diameter (4.1–5.5 mm) increased as age increased. Fecundity increased across all four reproductive age‐classes of Rio Grande Silvery Minnow, with the larger portion of total fecundity occurring in the first spawn across all age‐classes. The timing of spawning with optimal conditions in the Rio Grande is critical for survival and ultimately recruitment into the wild fish population.

The decline and endangerment of native fish has led to an increase in hatcheries that sustain and augment threatened and endangered species. In an effort to restore self‐sustaining populations, hatchery‐reared Bonytail (Gila elegans) are released into the lower Colorado River annually. Current augmentation protocols for Bonytail require a minimum stocking size of 300 mm total length due to greater apparent survival of larger individuals. The fish culture process of reaching this desired target size requires multiple years of growth, during which precocious individuals regularly spawn. Recruitment in production ponds increases densities, potentially reducing growth rates and adversely affecting culture conditions. Polyculture techniques have been shown to have synergistic effects and under proper conditions effectively control unwanted biota. In an effort to address the management implications of Bonytail recruitment on adult growth and survival, we tested the use of a historically co‐occurring piscivore, Colorado Pikeminnow (Ptychocheilus lucius), as a biological control agent. Colorado Pikeminnow effectively controlled Bonytail recruitment and had a positive effect on adult growth rates. Our results suggest polyculture of these two species can aid management actions by increasing augmentation efforts.