Sauger Research Articles

Anisakid nematode larvae in freshwater fishes in the St. Lawrence River (Québec, Canada)

Anisakid nematodes were observed in freshwater and anadromous fishes in the St. Lawrence River, Québec, Canada. Fish were caught at different locations across a 250 km gradient in the St. Lawrence ecosystem covering freshwater and estuarine habitats. Depending on the sampling sites, nematode prevalence ranged from 30% to 58% for sauger (Sander canadensis) and was 43% for Atlantic tomcod (Microgadus tomcod). For walleye (Sander vitreus), parasites were found only in a fluvial Lake (Lake Saint-Pierre) of the St. Lawrence River, with a prevalence of 23%. In all sampling sites, mean abundance of nematodes in the flesh was higher in sauger than in walleye. Presence of nematodes was significantly correlated with fish total length for walleye, sauger and Atlantic tomcod. Sealworm, Phocanema decipiens s.s., and whaleworm, Anisakis simplex s.s., were found and identified by molecular analysis in sauger and walleye in a fluvial lake (Lake Saint-Pierre), the fluvial estuary and the upper estuary of the St. Lawrence River, while Atlantic tomcod were found infected in a freshwater river tributary (Sainte-Anne River) during spawning.This is the first record of Ph. decipiens s.s. in a non-anadromous freshwater fish. The presence of sealworm and whaleworm in walleye and sauger is attributed to their forays into the brackish waters of the fluvial estuary and suggest large scale migrations between the brackish and the fresh waters of the St. Lawrence River.

Effects of activation and assisted reproduction techniques on the composition, structure, and properties of the sauger (Sander Canadensis) spermatozoa plasma membrane

The sperm plasma membrane is a multifunctional organelle essential to fertilization. However, assisted reproduction techniques often negatively affect this structure, resulting in reduced fertility. These reductions have been attributed to plasma membrane damage in a wide array of species, including fish. Considerable research has been conducted on the fish sperm membrane, but few have examined the effect of cryopreservation and other assisted reproduction techniques (ARTs) on not only membrane composition, but also specific characteristics (e.g., fluidity) and organization (e.g., lipid rafts). Herein, we determined the effects of three ARTs (testicular harvest, strip spawning, and cryopreservation) on the sperm plasma membrane, using Sauger (Sander canadensis) sperm as a model. To this end, a combination of fluorescent dyes (e.g., merocyanine 540, filipin III, cholera toxin subunit β), liquid chromatography – mass spectroscopy (LC-MS) analysis of membrane lipids, and membrane ultracentrifugation coupled with plate assays and immunofluorescence were used to describe and compare sperm fluidity, membrane composition, as well as lipid raft composition and distribution among sperm types. Stripped sperm became more fluid following motility activation (40% increase in highly fluid cells characterized by a 2 × increase in fluorescence) and contained lipid rafts restricted to the midpiece. Testicular harvest yielded sperm with characteristics similar to stripped sperm. By contrast, cryopreservation impacted every aspect of membrane physiology. Two cell populations, one highly fluid and the other rigid, resulted from the freeze-thaw process. Cryopreservation reduced lipid raft cholesterol content by 44% and flotilin-2 (a lipid raft marker) was partially displaced owing to a decrease in buoyancy. Unlike stripped and testicular sperm, LC-MS analysis revealed increases in oxidative damage markers, membrane destabilization, and apoptotic signaling in cryopreserved sperm. Ultrastructural analysis also revealed widespread physical damage to the membrane following freeze-thaw. Sperm motility, however, was unrelated to any measure of membrane physiology used in this study. Our results demonstrate that ARTs have the potential to substantially affect the sperm plasma membrane, but not always detrimentally. These results provide multiple potential biomarkers of sperm quality as well as insight into sources of sub-fertility resulting from use of ARTs.

Diet influences survival and growth of intensively reared larval saugeye (Sander vitreus × Sander canadensis)

AbstractWe evaluated the performance of five commercial microstarter diets (Otohime, Gemma Micro, Gemma Wean, Optimal Starter, and Omega One Fry) fed to first feeding larval saugeye Sander vitreus × Sander canadensis. Triplicate tanks of 2500 larvae (initial weight: 2.6 ± 0.6 mg) were stocked at 4 days post‐hatch (DPH) and fed treatment diets for 4 weeks. Fish were randomly sampled each week to monitor growth and development. Superior growth performance was observed in fish fed Otohime and Gemma Micro and was statistically significant as early as 13 DPH. At the conclusion of the trial, fish fed Otohime and Gemma Micro were approximately 3.6 times heavier than fish fed Gemma Wean and Optimal Starter. Survival was highest in fish fed Otohime (39.7% ± 7.1%), with Gemma Micro performing second best (14.1% ± 3.3%). Survival of fish fed Omega One Fry was too low for analysis (0.70 ± 1.1). Incidence of deformity among the dietary treatments ranged from 0% to 10.7%, primarily manifesting as a malformation of the jaw. Our results highlight the importance of diet for successfully raising saugeye through the larval/juvenile stage, and provide key information for this critical bottleneck in percid culture.

Fish Exhibit Distinct Fluorochemical and δ15N Isotopic Signatures in the St. Lawrence River Impacted by Municipal Wastewater Effluents

We examined the influence of Montreal wastewater treatment plant (WWTP) effluents on two top predators, Walleye (Sander vitreus) and Sauger (Sander canadensis), with a focus on δ15N isotopic signatures and per- and polyfluoroalkyl substances (PFAS). These two fish species were collected in the summer 2013 in the St. Lawrence River upstream and downstream from a major WWTP, as well as in background sites (semi-remote lakes). Most of the δ15N variations for Sauger and Walleye are attributable to 1) δ15N values of the primary producers and sewage-derived particulate organic matter (SDPOM) at the base of the trophic food chain, 2) agricultural activities combined with biogeochemical processes, and 3) food web length. δ15N was significantly lower in fish collected in the effluent-mixed water masses than other sites of the St. Lawrence River, attributed to the SDPOM of the WWTP effluent. Relative to the background sites, certain PFAS were present at much higher levels in the St. Lawrence River, with profiles dominated by perfluoroalkyl sulfonates (PFSA). However, PFSA profiles generally remained consistent along the St. Lawrence River. PFOS levels in fish from the St. Lawrence exceeded the current Federal Environmental Quality Guidelines for protecting piscivorous mammals or birds. However, the human chronic daily intake of PFOS remained below current thresholds suggested by national agencies.

Spatial and Temporal Changes in Testis Morphology and Sperm Ultrastructure of the Sportfish Sauger (Sander canadensis)

AbstractThe objective of this study was to assess testicular morphology and spermatozoal structure spatially within the reproductive tract and temporally among seasons in the sauger (Sander canadensis). The testis exists as two separate lobes joined at the urogenital pore and were characterised as unrestricted lobular with seminiferous tubules terminating at the ventral periphery and coalescing dorsally on the main sperm duct. Differences were observed between the pre‐breeding season (November) and breeding season (March), with every stage of spermatogenesis occurring in spermatocysts in pre‐breeding season in contrast to only spermatozoa being present in the tubules and main duct during the breeding season. Longitudinal folds in the main duct epithelium increased in number with increasing proximity to the urogenital pore, greatly increasing epithelial height regardless of season. Sauger spermatozoa consisted of an ovoid head, a midpiece containing 2 – 4 mitochondria incorporated into the head and a single flagellum containing an asymmetrical lateral ribbon. Motile spermatozoa were found throughout the testis during the breeding season. A decrease in sperm concentration was quantified moving proximally, suggesting a hydration effect by the main duct epithelium during the breeding season. These observations fill an important knowledge gap regarding reproductive biology of this impactful recreational fish species.

Changes to the spermatozoa glycocalyx and its role in fertilization in Sauger (Sander canadensis)

The spermatozoa glycocalyx is a dynamic coating of extracellular glycoproteins known to facilitate the acrosome reaction and fertilization in mammals. Most fish sperm, however, contain no acrosome and are subjected to different stimuli (e.g., osmotic shock in the external environment) prior to fertilization. At present, our understanding of the composition and spatial distribution of sugar moieties and the functional role of the glycocalyx in fish sperm remains incomplete. Moreover, the influence of assisted reproduction techniques (e.g., testicular harvest and cryopreservation) commonly used in aquaculture settings on this structure in fish sperm is unknown. Herein, we describe and compare the composition and characteristics of the glycocalyx among sperm types (stripped, testicular, and cryopreserved) and between activation statuses (inactive vs. activated) using sauger (Sander canadensis) as a model. We also investigated the importance of certain moieties (e.g., N-acetyl-glucosamine [GlcNAc]) to fertilization. Staining distributions, fluorescent intensity, and proportion of cells exhibiting high fluorescence were measured for each treatment using fluorescent microscopy and flow cytometry, respectively. Three lectins, specific to certain glycocalyx sugar moieties (wheat germ agglutinin, WGA [GlcNAc]; concanavalin A, ConA [α-mannose]; and peanut agglutinin, PNA [β-galactose]) were used to monitor these variables in fish sperm. The sauger glycocalyx contained GlcNAc and α-mannose but lacked β-galactose moieties. Testicular sperm exhibited fewer cells (20–40% fewer) with high GlcNAc and α-mannose content than other sperm types. Additionally, the proportion of highly fluorescent cells in testicular sperm were positively correlated with motility (r = 0.80–0.95), suggesting the glycocalyx is affected by post-testicular maturation. Motility activation via hypo-osmotic shock caused a redistribution of GlcNAc to the apical region of the head of 40–50% of stripped and testicular sperm, respectively. Cryopreserved sperm showed significantly reduced apical staining following activation (< 5%) and a 2 to 3-fold increase in α-mannose availability. Further, fertilization was reduced by ~80% compared to a fresh control (i.e., untreated stripped sperm) in both stripped sperm pre-treated block GlcNAc during insemination and cryopreserved sperm. These results indicate that the glycocalyx of sauger sperm is dynamic, as it is modified during post-testicular maturation, motility activation, and that it plays a pivotal role in fertilization. Cryopreservation largely negated these changes, which may partially explain the reduced fertility observed in frozen sperm. Ultimately, our analyses show that the use of lectins (e.g., GA and ConA) as biomarkers for the glycocalyx can help to understand the quality and fertilization potential of fish sperm.

Mercury concentrations in commercial fish species from Lake Winnipeg, 1971–2019

Concentrations of total mercury (THg) in the axial musculature of northern pike (Esox lucius), walleye (Sander vitreus), lake whitefish (Coregonus clupeaformis), and sauger (Sander canadensis) were analyzed from several regions of Lake Winnipeg and three main inflows, focusing on Mossy Bay in the North Basin of the lake. Length-standardized means (standard means) indicated THg concentrations in pike of 550 mm fork length (0.44 ppm) and walleye measuring 400 mm (0.38 ppm) from Mossy Bay were highest in 1971 and declined to 0.13 and 0.22 ppm, respectively, by 1974. Standard means of both these species have been similar since 2010 (walleye; approximately 0.11 ppm) and 2013 (pike; approximately 0.17 ppm), except for a significant increase to 0.15 ppm in walleye in 2019, potentially related to concurrent changes in trophic interactions with invasive fish and invertebrate species. Standard means of 300 mm long sauger (0.23–0.29 ppm) did not decline significantly between 1971 and 1974, and those of 350 mm long whitefish ranged from 0.006 to 0.028 ppm from 1983 to 2016 with no clear temporal trend. In concert with data from other areas of Lake Winnipeg and the three inflows for 2000–2019, these results indicate higher contemporary concentrations in the South Basin of the lake. This latitudinal gradient in fish THg is assumed to be a result of continuous mercury inputs from the Red and the Winnipeg River, whereas a former point source of industrial mercury in the Saskatchewan River is no longer relevant. According to human consumption limits based on tolerable daily intake calculations and current THg concentrations of fish from Mossy Bay, substantial quantities of whitefish, pike, and walleye fish can be safely eaten.

Spontaneous hybridization and introgression between walleye (Sander vitreus) and sauger (Sander canadensis) in two large reservoirs: Insights from genotyping by sequencing.

Anthropogenic activities may facilitate undesirable hybridization and genomic introgression between fish species. Walleye (Sander vitreus) and sauger (Sander canadensis) are economically valuable freshwater species that can spontaneously hybridize in areas of sympatry. Levels of genomic introgression between walleye and sauger may be increased by modifications to waterbodies (e.g., reservoir development) and inadvertent propagation of hybrids in stocking programs. We used genotyping by sequencing (GBS) to examine 217 fish from two large reservoirs with mixed populations of walleye and sauger in Saskatchewan, Canada (Lake Diefenbaker, Tobin Lake). Analyses with 20,038 (r90) and 478 (r100) single nucleotide polymorphisms clearly resolved walleye and sauger, and classified hybrids with high confidence. F1, F2, and multigeneration hybrids were detected in Lake Diefenbaker, indicating potentially high levels of genomic introgression. In contrast, only F1 hybrids were detected in Tobin Lake. Field classification of fish was unreliable; 7% of fish were misidentified based on broad species categories. Important for activities such as brood stock selection, 12 of 173 (7%) fish field identified as pure walleye, and one of 24 (4%) identified as pure sauger were actually hybrids. In addition, two of 15 (13%) field‐identified hybrids were actually pure walleye or sauger. We conclude that hybridization and introgression are occurring in Saskatchewan reservoirs and that caution is warranted when using these populations in stocking programs. GBS offers a powerful and flexible tool for examining hybridization without preidentification of informative loci, eliminating some of the key challenges associated with other marker types.

Spatial Gradients in Population Characteristics of Ohio River Sauger and Implications for a Length‐Based Regulation

AbstractSauger Sander canadensis provide a popular, harvest‐oriented fishery throughout the Ohio River and are managed jointly by the state fisheries resource agencies through the Ohio River Fisheries Management Team. For more than two decades, the Ohio River Sauger population has been dominated by small (&lt;356 mm), young (&lt;3 years old) individuals. Recently, Sauger abundance in the Ohio River has been near or below long‐term averages. Together, these observations prompted concern that overfishing may be occurring and that more restrictive harvest regulations may be necessary. We summarized Sauger population characteristics (abundance of age‐0 Saugers, abundance of Saugers ≥280 mm TL, growth, and mortality) based on data from Ohio River Fisheries Management Team population assessments conducted during the period of 2005–2017 and modeled the potential outcomes of applying a 356‐mm minimum length limit. During the period 2005–2017, abundance of age‐0 Saugers and abundance of Saugers ≥280 mm TL was greater with distance downstream but generally declined through time. Growth rates and total annual mortality rates increased with distance downstream and had no apparent temporal trends. Yield‐per‐recruit models showed that where Saugers grow fastest (i.e., downstream pools), implementing a minimum length limit could improve size structure and increase yield. However, where Saugers grow slowly (upstream pools), size structure would only increase marginally, and yields would likely decrease with a minimum length limit. Upstream to downstream gradients in Sauger population characteristics may therefore lead to differences in the effectiveness of length‐based regulations among Ohio River pools. Fisheries managers must therefore consider trade‐offs between the size of fish at harvest and yield before implementing minimum length limits.

Testicular collections as a technique to increase milt availability in sauger (sander canadensis)

This study was conducted to compare quality and quantity of sperm collected from sauger (S. canadensis) using two collection methods: stripping alone and testicular tissue collection combined with stripping. Sperm were collected from sauger broodstock (n = 20) during the breeding season. Fish were randomly assigned to two sperm collection groups: (1) stripping once or (2) stripping twice before testicular tissue collection for obtaining additional sperm. Sperm motility variables, morphology, total number produced, and fertilization (%) were compared using the two collection methods. Testicular sperm had greater total motility (70.1 ± 2.1% compared with 44.3 ± 5.7%) but there were fewer morphologically normal cells (76.4 ± 1.3% compared with 92.8 ± 1.0%) compared to sperm collected using the stripping procedure. Sperm collection regimen utilizing testicular collections and sperm extractions in combination with stripping resulted in a ∼ten fold increase in total number of motile and morphologically normal sperm (39.5 ± 4.1 × 10 9) compared with the currently utilized two sequential sperm stripping collection procedures alone (3.6 ± 4.1 × 10 9 sperm). In large-scale studies (150,000 eggs), fertilization, using sperm collected from testicular tissues (1.0 × 105 motile sperm/egg), was similar to sperm collected with only the stripping procedure (71.2 ± 5.5 %, 81.2 ± 5.5 %, P = 0.265). The results of this study indicate testicular collection combined with sperm extractions allows for collection of sperm of a quantity and quality to maximize fry production and reduce the problems with lack of broodstock availability for sperm collection.

Evaluation of potential sources of sauger Sander canadensis for reintroduction into Lake Erie

Sauger (Sander canadensis) supported recreational and commercial fisheries in Lake Erie until the fishery collapsed in the early-1950s, with extirpation of sauger occurring soon after. Previous attempts to rebuild populations via stocking programs were unsuccessful, and the reasons for lack of success are unclear. The Ohio Department of Natural Resources-Division of Wildlife is re-examining the feasibility of reintroducing sauger because the current fish community and habitat conditions appear more suitable for sauger survival and proliferation. Selecting potential sources for reintroduction programs requires consideration of several factors. Donor and recipient ecosystems and life histories should be similar, the source population should have sufficient genetic diversity to withstand losses in diversity associated with hatchery practices, and the source and donor populations should have similar genetic diversity metrics and should be accessible while broodstock is developed. A review of the literature and a genetic analysis of historical sauger collections from Lake Erie and contemporary samples from possible donor populations in five different watersheds was performed to evaluate potential candidate sources for a re-introduction program. We compared genetic diversity, life history parameters, and ecosystem conditions of historical Lake Erie sauger to contemporary sauger populations from the Ohio River (Bellville, Meldahl, and New Cumberland pools), Missouri River, Ottawa River, Lake of the Woods, and Lake Winnebago. While life history and ecological conditions were similar across populations, there was genetic differentiation among potential donor sources and historical collections of sauger from Lake Erie, with contemporary populations from the Ohio River being most like historic Lake Erie sauger.

Interaction of sauger Sander canadensis and walleye Sander vitreus in a large, shallow northern river.

The objectives of this study were to: (1) determine the relative abundance of sauger Sander canadensis and walleye S. vitreus within the Rainy River using a standardized index netting technique; (2) assess the life-history characteristics of the two species in a northern river; (3) examine the spatial distribution of the two species; (4) assess year-class synchrony. At a larger scale, relative abundance of S. canadensis and S. vitreus were similar among sections of the river. However, at a finer scale, S. canadensis were the dominant species over more area (24%) of the river than S. vitreus (12%). Life-history traits for both species were within the range reported for North American. Mortality rates were similar, suggesting that anglers were not affecting one species more than the other. Year-class strengths were not synchronous between S. canadensis and S. vitreus (r = 0.07). There was evidence of S. canadensis potentially outcompeting S. vitreus with a strong year class of S. canadensis followed by a very weak class of S. vitreus. Additionally, S. canadensis were larger than S. vitreus in most sections of the river when adjusted for mean size. However, the potential interspecific competition was not to the exclusion of S. vitreus. Turbidity was probably the factor that enable S. canadensis to survive sympatrically with S. vitreus given their inability to segregate by depth within the river.

Long-Term Data Suggest Potential Interactions of Introduced Walleye and Smallmouth Bass on Native Sauger in Four Missouri River Impoundments

Abstract Sauger Sander canadensis, Walleye Sander vitreus, and Smallmouth Bass Micropterus dolomieu, are important sportfish in the four main stem Missouri River reservoirs in South Dakota: Lakes Oahe, Sharpe, Francis Case, and Lewis and Clark. However, native Sauger populations, once assumed to be stable, may be in decline. To identify temporal trends and potential interspecific mechanisms affecting Sauger populations, we examined their long-term abundance trends in standard gillnet surveys and angler catch and harvest trends in long-term creel surveys. We also used a robust design occupancy model to examine changes in within-lake distribution of this species. There are concerns regarding the effects of Walleye and Smallmouth Bass on Sauger, so we also described the population trends of these potential competitors. Standard gillnet surveys indicated declining abundance of both Sauger and Walleye in Lakes Oahe and Sharpe. Sauger abundance has trended down in Lewis and Clark, but upward in Francis Case. Conversely, Walleye abundance trends declined in Francis Case and increased in Lewis and Clark. Occupancy (ψ̂) of Sauger declined in all four reservoirs, indicating a contracting distribution throughout the reservoirs. Walleye occupancy remained ∼1.0. Smallmouth Bass occupancy increased in the three reservoirs with sufficient data for analysis, excluding Lewis and Clark Lake. Smallmouth Bass exhibited steady increases in angler catch and harvest, as well as abundance in long-term gillnet surveys, suggesting expanding and increasing populations. Habitat alteration is hypothesized to be a major driver of the Sauger occupancy and abundance declines. However, Walleye and Smallmouth Bass interactions could also be contributing to observed declines of native Sauger.

Genetic tagging is an effective way to monitor survival of released hatchery saugers: Conservation efforts in the Wind River, Wyoming

ABSTRACTReleased hatchery-origin fish must survive and reproduce for supplementation to recover collapsed native populations, yet monitoring fitness is challenging, because physical tags are not passed from parent to offspring. Parentage-based tagging (PBT) is a method in which all captive-bred parents are genotyped (i.e., given a molecular tag), and their wild-caught hatchery offspring are identified via genetic pedigree analysis. The sauger (Sander canadensis) is a highly migratory, freshwater percid (perch species), native to central and eastern North America. In the Wind River basin, Wyoming the species’ abundance has declined considerably since 2002, and in 2013 stakeholders initiated a hatchery program to recover the population. We estimated the statistical sensitivity and accuracy of PBT using 17 microsatellites to identify hatchery-origin saugers captured in the wild. We completed in vitro and in silico experiments that demonstrated 98% sensitivity and 99% accuracy of PBT in distinguishing hatcher...

Growth rate and condition of walleye (Sander vitreus), sauger (Sander canadensis), and dwarf walleye in a large Canadian lake

The second largest inland walleye (Sander vitreus (Mitchill, 1818)) and sauger (Sander canadensis (Griffith and Smith, 1834)) fishery in Canada is found in Lake Winnipeg, Manitoba. To manage the fishery for a sustainable future, the growth and condition of these fish must be understood. Objectives were to (1) examine baseline growth and condition of walleye and sauger in Lake Winnipeg, (2) evaluate variation between the North and South basins, and (3) contribute observational findings on the distribution of dwarf walleye. Gill nets were set to catch walleye, sauger, and dwarf walleye throughout both basins at various locations and in all seasons during 2010 and 2011. North Basin walleye and sauger had higher growth rates and condition relative to the South Basin. This may be due to differential exploitation rates or diets such as the consumption of invasive rainbow smelt (Osmerus mordax (Mitchell, 1814)) in the North Basin and not in the South Basin. Dwarf walleye were observed more frequently in the South Basin than in the North Basin. Overall, this study provides important baseline data on the growth and condition of walleye and sauger populations prior to invasion of the spiny waterflea (Bythotrephes longimanus Leydig, 1860) and zebra mussels (Dreissena polymorpha (Pallas, 1771)).

Population Demographics of Sauger and Simulated Effects of Minimum Length Limits in the Kaskaskia and Ohio Rivers

Abstract Sauger Sander canadensis are a popular sport fish native to large turbid midwestern rivers and are in decline across much of their range due to habitat loss and exploitation. Specifically, within the lower Kaskaskia and Ohio rivers, Sauger are managed under different harvest regulations and a knowledge gap exists regarding the current status of both populations as well as the effects of the harvest regulations on the size and age structures of both populations. We collected Sauger by nighttime boat electrofishing during early winter 2014–2016 and used otoliths to age all fish. Sauger stocks in both rivers exhibited fast growth rates and high annual mortality rates. Yield-per-recruit modeling indicated that the current 356-mm minimum size limit for Sauger in the Kaskaskia River is sufficient to prevent growth overfishing and likely explains the consistently larger size structure (greater proportion of fish ≥356-mm total length) of Sauger sampled from the Kaskaskia River compared with the Ohio River. Modeling suggested that growth and recruitment overfishing of Sauger are likely occurring in the Ohio River with no minimum length limit based on available exploitation estimates for Sauger in the lower Ohio River. Implementing a 356-mm minimum length limit for Sauger in the lower Ohio River is predicted to prevent growth and recruitment overfishing based on available exploitation rate estimates and would be consistent with the statewide minimum length limit for Sauger in Illinois and minimum length limits on two major tributaries (Tennessee and Cumberland rivers downstream of Kentucky and Barkley lakes, respectively).

Increasing saugeye (S. vitreus × S. canadensis) production efficiency in a hatchery setting using assisted reproduction technologies

Assisted reproductive technologies (ART) are used to increase fertilization rates in a number of animal species. However, their use with sauger (Sander canadensis), the paternal contributor in the production of the recreationally and economically important saugeye (Sander vitreus × S. canadensis), is limited. State fishery management agencies are periodically unable to meet saugeye production goals due to the inability to collect sufficient numbers of sauger broodstock, as well as a lack of protocols for standardized sperm use during production. Therefore, the need exists to overcome sauger sperm limitation during the saugeye production season using ARTs. Toward this end, we investigated the effect of human chorionic gonadotropin (hCG) on sperm production, determined an efficient sperm-to-egg ratio for fertilization, and validated the use of a densimeter to measure sauger sperm cell concentration for precise sperm addition during fertilization. The effect of hCG on sperm production was evaluated by comparing pre- and post-treatment milt parameters between fish treated with either hCG or saline (control). Treating fish with hCG increased sperm volume relative to saline controls (hCG 0.64 ± 0.19 mL/kg; control: 0.31 ± 0.05 mL/kg). However, sperm cell concentration and total sperm production were unaffected. To determine an efficient sperm-to-egg ratio, fresh milt from several individuals was pooled and used to fertilize walleye eggs at three sperm-to-egg ratios (20,000, 50,000, and 100,000 sperm/egg). The range of sperm-to-egg ratios used in this study did not significantly affect fertilization rates (20,000: 82.67 ± 3.38%, 50,000: 91.33 ± 2.67% and 100,000: 88.67 ± 3.44%). Lastly, by using linear regression to compare densimeter and hemocytometer estimates in serially diluted sperm we were able to accurately estimate hemocytometer estimates (R2 = 0.96, p < 0.05). In conclusion, our study provides tools and standards that can be implemented by hatchery staff to increase saugeye production efficiency and lay the foundation for using ART for sauger and other fish species.

Swimming performance of sauger (Sander canadensis) in relation to fish passage

A lack of information on the swimming abilities of sauger (Sander canadensis), a highly migratory species particularly sensitive to habitat fragmentation, may inhibit the design of effective passage structures for this species. Passage success, maximum ascent distances, and maximum sprint velocities of sauger were estimated in an open-channel flume over a range of water velocities (51, 78, and 92 cm·s−1) and temperatures (10.0, 14.3, and 18.3 °C) to assess swimming performance. Passage success was high (91%) over all test velocities, as was the maximum instantaneous burst velocity (219 cm·s−1). Water temperature and body size had little effect on swimming performance. Sauger transitioned from steady, sustained swimming to unsteady, burst–glide, or steady burst swimming at 97 cm·s−1. Sauger were capable of sustained sprints of 124 cm·s−1over 15 s duration in a swim chamber. Results suggest passage structures with water velocities less than 97 cm·s−1should provide high probability of successful passage of adult sauger, whereas structures with water velocities exceeding 219 cm·s−1may be impassable.

Genetic Stock Assessment and Hatchery Contributions of Sauger Stocked into Old Hickory Lake, Tennessee

Abstract Sander canadensis (Sauger) once supported a viable fishery in many of the reservoirs throughout Tennessee; however, these populations have experienced widespread declines. To improve population numbers, the Tennessee Wildlife Resources Agency began stocking Sauger in 1992 in Tennessee and Cumberland river impoundments. Here we examine the percent contribution of hatchery-stocked Sauger to the wild population in Old Hickory Lake, a mainstem impoundment on the Cumberland River. We determined the contribution of hatchery-stocked Sauger using microsatellite markers and a categorical allocation-based parentage analysis. We also evaluated measures of genetic diversity, including estimates of heterozygosity and effective population size. Genetic variation was comparable to other stocked populations of percids. However, estimates of effective population size were low and the contribution of hatchery-reared Sauger to natural populations was moderate, averaging 25.8% across sampled year classes. Despite hi...

Sympatric walleye Sander vitreus and sauger Sander canadensis in large reservoirs: Variable isotopic niche size and overlap across multiple time scales

AbstractWalleye Sander vitreus (Mitchill) and sauger Sander canadensis (Griffith &amp; Smith) may occupy similar niches in sympatric populations, but their long‐term resource use is poorly studied. Multi‐tissue (liver, muscle and bone) isotopic niche analyses were used to compare resource use by these species in two large reservoirs in Saskatchewan, Canada. Population isotopic niches were larger for sauger (1.73‰2–3.60‰2) than walleye (0.51‰2–2.61‰2) in Lake Diefenbaker, but opposite in Tobin Lake (sauger = 0.54‰2–2.57‰2; walleye = 1.30‰2–2.94‰2). Analyses of population overlap suggest that these species co‐exist via niche partitioning, but partitioning was more pronounced in Lake Diefenbaker (overlap = 6%–38%; Tobin Lake overlap = 18%–62%). The size of individual niches and levels of intra‐ and interspecific overlap among individual fish also varied with reservoir. This study shows that walleye and sauger use different resources across different time scales, but the degree of partitioning can vary markedly with environment.