Downloaded by [University of Saskatchewan Library] at 04:30 04 February 2015Fisheries | www.fisheries.org 7 FEATURE Ampliando el paradigma de manejo de la regulación de ríos: la olvidada zona muerta como obstáculo para la recuperación del esturión pálido La proliferación de presas a nivel global durante el último medio siglo, ha llevado a los ecólogos a tratar de comprender los efectos que tiene la regulación de ríos sobre los grandes peces de agua dulce. Actualmente, gran parte de los esfuerzos dirigidos a mitigar la influencia de las presas en los grandes peces de agua dulce se han enfocado en los efectos observados en la porción inferior de las cuencas y poca atención se le ha dado a los efectos río-arriba. A través de una combinación de observaciones de campo y experimentos de laboratorio, se probó la hipótesis de que las condiciones abióticas río-arriba en las presas son el mecanismo que explica las fallas del reclutamiento del esturión pálido (Scaphirhynchus albus), una icónica especie de agua dulce, de gran tamaño, catalogada como amenazada. Se muestra por vez primera que la anoxia en hábitats río-arriba en los reservorios (i.e., zonas de transición entre ríos y reservorios) es probablemente responsable de las fallas en el reclutamiento del esturión pálido. Las condiciones de anoxia en la zona de transición es función de la reducción de la velocidad de flujo del río y la concentración de material orgánico fino particulado, con un alto contenido de respiración microbiana. Como se predijo, las condiciones del río por encima de la zona de transición fueron óxicas en todos los sitios de muestreo. Los resultados indican que las zonas de transición representan un sumidero para el esturión pálido, Se argumenta que los ecólogos, ingenieros y tomadores de decisiones requieren de ampliar el paradigma de la regulación de ríos, con el objeto de incluir los efectos que tienen las presas tanto río-arriba como río-abajo y, así mismo, mitigar sistemáticamente los ecosistemas afectados en beneficio de los grandes peces de agua dulce, especialmente el esturión pálido.The global proliferation of dams within the last half century has prompted ecologists to understand the effects of regulated rivers on large-river fishes. Currently, much of the effort to mitigate the influence of dams on large-river fishes has been focused on downriver effects, and little attention has been given to upriver effects. Through a combination of field observations and laboratory experiments, we tested the hypothesis that abiotic conditions upriver of the dam are the mechanism for the lack of recruitment in Pallid Sturgeon (Scaphirhynchus albus), an iconic large-river endangered species. Here we show for the first time that anoxic upriver habitat in reservoirs (i.e., the transition zone between the river and reservoir) is responsible for the lack of recruitment in Pallid Sturgeon. The anoxic condition in the transition zone is a function of reduced river velocities and the concentration of fine particulate organic material with high microbial respir...

No abstract

Reports from hatcheries have demonstrated that commercially available diets are inadequate for June Suckers Chasmistes liorus and suggest that fish quality can be improved through species‐specific diet optimization. To determine dietary protein and lipid levels for juvenile June Suckers, practical‐type diets were formulated with 35, 40, or 45% protein and 8, 12, or 16% lipid and tested in a 3 × 3 factorial design. Two additional diets (45% protein and 16% lipid [45:16] without dicalcium phosphate supplementation and 45:16 with 2× dicalcium phosphate) were formulated to test the necessity of dicalcium phosphate supplementation. Each diet was fed to three replicate tanks (average initial fish weight ± SD = 4.48 ± 0.24 g) of fish per treatment (85 fish/tank); only duplicate tanks were used for the nondicalcium phosphate‐supplemented treatment. Fish were reared in 80‐L tanks supplied with 4 L/min of 22°C spring water and fed 6–4% body weight (BW)/d by automated belt feeders, 6 d/week. At the end of 12 weeks of culture, tissue samples were obtained to determine nutrient partitioning. An acute temperature challenge was also conducted to investigate dietary adequacy. Significant effects of diet on growth and temperature tolerance were observed. Fish fed the diet with 45% crude protein gained more weight than did fish fed 40% or 35% crude protein, and fish fed 16% dietary lipid gained more weight than did fish fed 12% and 8% crude lipid. However, the composition of this growth indicated that fish fed the 16% lipid stored larger amounts of lipid in both the visceral cavity and the muscle. A significant negative interactive effect of dietary protein and lipid on temperature tolerance was observed at 45% crude protein and 16% lipid. Results of this study define acceptable ranges of dietary protein and lipid for juvenile June Suckers and provide culturists information to make better choices regarding appropriate diets for this species.

Nonlethal tools (plasma sex steroid concentrations and ultrasound) for assigning sex and reproductive condition in Burbot Lota lota from Lake Roosevelt, Washington, were assessed. Gonadal tissue, blood plasma, and gonadal sonograms were collected monthly from November 2016 to March 2018. Gametogenesis was described by gonadal histology during an entire reproductive cycle to confirm sex and reproductive condition. Plasma testosterone (T) and estradiol‐17β (E2) concentrations were measured by radioimmunoassay. Plasma 11‐ketotestosterone (11‐KT) concentrations were measured by liquid chromatography–mass spectrometry. Plasma sex steroid profiles, gonadosomatic index, and ovarian follicle diameter were also described during an entire reproductive cycle. Plasma 11‐KT concentration was used to assign sex with 82% accuracy during the entire reproductive cycle, and plasma 11‐KT and E2 concentrations were used to assign sex with 98% accuracy when fish were reproductive (i.e., November–March in Lake Roosevelt). Plasma T and E2 concentrations were used to assign reproductive condition in females with 98% accuracy, and plasma T concentration was used to assign reproductive condition in males with 90% accuracy. Ultrasound was used to assign sex with 96% accuracy but was not useful for assigning reproductive condition. Nonlethal tools to assign sex and reproductive condition will enable fisheries biologists to assess reproductive indices of the Burbot population in Lake Roosevelt to inform management decisions.

Winter hypoxia in shallow, ice‐covered lakes can be a significant limiting factor for overwintering fish populations. In this study we tested the hypothesis that low overwinter survival due to winter hypoxia is a limiting factor for a rare, adfluvial population of native Arctic Grayling Thymallus arcticus inhabiting Upper Red Rock Lake, Montana. We used a combined laboratory and telemetry study to document the extent of hypoxia over two winters and to assess the physiological tolerance, behavioral response, and winter survival in relation to hypoxia. In the laboratory, we observed a significant behavioral and physiological response to dissolved oxygen (DO) levels ≤ 4.0 mg/L and determined acute 24‐h LC50 values (concentration lethal to 50% of test fish) of 0.75 mg/L DO for adults and 1.50–1.96 mg/L for juveniles at temperatures of 1–3°C. In the field study, we observed dynamic DO concentrations (DO < 1.0 to 10.0 mg/L) during winter ice cover, ranging from persistent near‐anoxic conditions near the bottom to DO concentrations > 4.0 mg/L in the epilimnion. Radiotelemetry indicated adult winter survival rate was high (0.97 in 2014, 0.95 in 2015) and that telemetered fish selected deeper (>1 m), more oxygenated habitat during ice cover. Our study demonstrated that Arctic Grayling have a high tolerance to acute hypoxia exposure and exhibit a physiological and behavioral stress response to DO concentrations ≤ 4.0 mg/L. Although hypoxia was present in parts of the lake, sufficient suitable habitat with DO > 4.0 mg/L was available in the lake epilimnion in both study winters. However, winter conditions more severe than those observed during our 2‐year study occur periodically in the lake, and thus winterkill could still be a limiting factor for the population.

The June sucker Chasmistes liorus is an endangered adfluvial fish species that is endemic to the Utah Lake basin. This species remains endangered due to a lack of recruitment. Anthropogenic changes to June sucker lotic and lentic habitat has likely led to recruitment failure. Changes to Utah Lake include increased water temperature, increased turbidity, and eutrophic and saline conditions. The remaining spawning habitat for June suckers in the Provo River has experienced flow, temperature, and channelization modifications. We tested the hypothesis that recruitment failure is caused by a thermal shock that occurs when larvae are transported in the drift out of the Provo River (12-198C) and into Utah Lake (17-258C). We used two laboratory methods-direct transfer and acclimated chronic exposure (ACE)-to determine (1) the upper lethal temperature (ULT) and (2) the acute and chronic mortality associated with larval exposure to an acute thermal shock. The ULT of larvae acclimated to 168C was 338C. Survival varied from 81% to 95% for larvae that were directly transferred from 168C (acclimation temperature) to 19-298C and held for 7 d; survival was not significantly different from that of the 168C control. A modified ACE method was used to mimic the riverto-lake transition. Acclimation temperatures of 12, 16, and 198C were increased by 5-88C over 4-6 h. After approximately 30 d, survival ranged from 42% (transition from 168C to 218C) to 87% (transition from 198C to 278C). Mean weight of fish that received the 19-278C transition treatment was significantly greater than that of all other treatment groups except the 19-258C transition group. Warmer incubation and rearing temperatures led to increased growth and survival. We conclude that thermal shock does not explain June sucker larval recruitment failure in Utah Lake, and we suggest that other factors are responsible for the recruitment failure.

Gonad size (diameter and circumference) measured by ultrasound was assessed as a metric to assign stage of maturity in Burbot Lota lota from Lake Roosevelt, Washington.  Paired gonad tissue and ultrasound measurements were collected monthly from November 2017 to March 2018.  Gonad tissue was processed for histological analysis to confirm stage of maturity.  Gonad diameter and circumference were measured by ultrasound.  Excised gonad diameter (i.e., true gonad diameter) was measured by digital calipers, and excised gonad circumference (i.e., true gonad circumference) was measured by a measuring tape.  All late vitellogenic (stage 6) ovaries measured by ultrasound had a diameter greater than 3.90 cm, suggesting a value of 3.90 cm or greater may be used to characterize females capable of spawning in the current reproductive cycle.  One mid-spermatogenic (stage 3) and all ripe (stage 4) testes were too large to be measured and assigned diameter of 5.11 cm, the maximum value capable of being measured by our ultrasound transducer.  A value of 5.11 cm or greater may be used to characterize males capable of spawning in the current reproductive cycle.  Testis circumference measured by ultrasound is not reported because some testes were wider than the ultrasound transducer and could not be measured.  Measurements of testis diameter did not differ between measurement methods (ultrasound vs. true), but ultrasound measurements of ovary diameter and circumference were higher than true measurements.  We attributed the difference between measurement methods to flattening of ovary while applying the ultrasound transducer.  Gonad diameter and circumference measured by ultrasound were highly correlated with gonadosomatic index and ovarian follicle diameter indicating gonad size measured by ultrasound is an appropriate index of gonad development in Burbot.

Five commercial diets and two formulated feeds were fed to initial‐feeding Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri fry and Snake River cutthroat trout O. clarkii spp. (currently being petitioned for classification as O. clarkii behnkei) fry for 18 weeks from June 16 to October 18, 2006, to evaluate fish performance. Eyed eggs from Yellowstone and Snake River cutthroat trout were received from the Yellowstone River State Fish Hatchery and Jackson National Fish Hatchery, respectively. Each diet was fed to four tanks of each subspecies of cutthroat trout (7 diets × 4 tanks/diet × 2 cutthroat trout subspecies = 56 tanks). Skretting Nutra‐Plus provided optimal fish weight, total length, survival, and feed conversion for Yellowstone cutthroat trout. The weight and total length of Snake River cutthroat trout were also greatest when fish were fed Skretting Nutra‐Plus. Skretting Nutra‐Plus is no longer available, but Skretting/Bio‐Oregon Bio‐Vita is very similar; this feed and similar premium feeds from other manufacturers should be considered for future cutthroat trout propagation programs.