In light of recent genetic investigations, the Weber River Green Sucker (Pantosteus virescens) has been taxonomically split from Bluehead Sucker (Catostomus discotomus). This new designation could entail Green Sucker being listed as an S1 species in Utah due to its reduced range, low population sizes, and threats to extirpation. Throughout Utah, populations of Green Sucker have undergone range-wide reductions (Budy et al. 2015), with declines in recruitment of Weber River populations being a significant concern over the last decade (Webber et al. 2012; Maloney 2017; UDNR 2020). Decimating factors that are likely limiting recruitment include: invasive species predation and competition, altered flow and thermal-regime, and limited backwater habitat (Webber 2012; Maloney 2017). However, hatchery rearing of streamside spawned Weber Green Sucker suggests that thiamine levels might also be reducing the survival of young-of-year. Thiamine (vitamin-B1) cannot be synthesized by fishes directly and must be absorbed from their environment or ingested through their diet. Without adequate thiamine levels in eggs, the fish larvae are not able to develop. Fry from the Weber River that were hatched and reared at UDWR's Logan Hatchery exhibited clinical signs of thiamine deficiency complex (TDC) and concomitant mortality. Due to the early mortality observed in developing fry and the TDC clinical signs being ameliorated by a thiamine bath (R. Shields, UDWR, personal communication), it is possible that the wild, maternal broodstock were thiamine deficient (Harder et al. 2018). This observation led to the prioritization of investigating potential thiamine deficiencies in Weber River Green Sucker for Utah's Northern Region by UDWR for FY 22 (UDNR 2020). Thiamine deficiencies in fishes can result from either not enough available thiamine in the environment and/or forage base (Balk et al. 2016; Ejsmond et al. 2019), or from thiamine being destroyed by eating a diet high in the enzyme thiaminase (Harder et al. 2018; Honeyfield et al. 2005). In aquatic ecosystems, thiamine is produced by phytoplankton, bacteria, and fungi, and thiamine enters the food web through these lower trophic level sources (Webb et al. 2007; Sañudo-Wilhelmy et al. 2014; Harder et al. 2018). Eggs and yolk sac fry receive virtually all their thiamine via maternal transfer, and it has been demonstrated that supplemental thiamine treatments for eggs can prevent mortality associated with thiamine deficiency in newly hatched fry (Futia and Rinchard 2017; Reed et al. 2023). Underlying mechanisms causing low thiamine levels in the environment and/or forage base are understudied and poorly understood (Harder et al. 2018). However, changes in the algal and bacterial communities of a system could alter the amount of available thiamine in the form of decreased thiamine production or increases of thiaminase (Malyarevskaya 1983; Wistbacka et al. 2002). In addition, exposure to contaminants, such as DDT, can increase thiaminase production and reduce thiamine levels in multiple taxa (Birger and Malyarevskaya 1977; Wistbacka et al. 2002). Conversely, mechanisms for how high levels of thiaminase enter the forage base for fishes is better understood. The most prevalent examples feature the overconsumption by piscivorous species of thiaminase rich forage fishes, such as Alewife (Alosa pseudoharengus) introduced into the Great lakes (Tillit et al. 2005) or highly prevalent Sprat (Sprattus sprattus) in the Baltic Sea (Karlsson et al. 1999). Detecting thiamine deficiencies in Bonneville Basin Green Sucker populations, especially those in the Weber River, could help identify a significant limiting factor for their recruitment. If wild stocks of Green Suckers are found to be thiamine deficient, then this could inform management decisions and could direct efforts to the reestablishment of a high thiamine and/or low thiaminase forage base for this species. Comparisons among thiamine levels in Green Sucker populations will allow for the detection of populations with healthy thiamine levels. This will allow managers to compare river drainage attributes, effluent impacts, invertebrate communities, and other parameters that are known covariates for thiamine level fluctuations in a system. Through these comparisons, targeted restoration efforts mitigating against factors that are likely limiting thiamine availability can be conducted to help bolster struggling Green Sucker populations. In addition, this research will help optimize UT hatchery methods currently used in Green Sucker production by providing optimum thiamine treatment dosages for thiamine deficient eggs.

Investigations into the thiamine levels of the Weber River Green Sucker populations should be conducted to: 1) Compare lower (Section 2) Weber River Green Sucker thiamine with other populations in the Bonneville Basin (upper Weber River and Raft River). 2) Develop an LC50 curve to determine what thiamine levels are detrimental to the development of young Green Sucker 3) Investigate if thiamine supplementation improves early rearing mortality of hatched Green Sucker fry 4) Compare thiaminase concentrations in periphyton from the Green Sucker population sample locations

This project is necessary now because there was a recent taxonomic split where Green Sucker were identified as a species that is distinct from Bluehead Sucker. There are relatively few Green Sucker populations in Utah and Green Sucker are a species of conservation interest. There are two major Green Sucker populations in Utah; in the Weber River and the Raft River. Numbers of Green Sucker in the Weber River have been declining and recent population estimates indicate that fewer than 100 Green Sucker remain in the river. It has been hypothesized that thiamine deficiency is impacting the survival of Green Sucker in the Weber River. This hypothesis is supported by informal research that has shown improvements in survival and health of hatchery raised Green Sucker following thiamine treatments. This study is intended to more thoroughly test whether thiamine deficiency is impacting the Weber River Green Sucker population. The results from the work will help inform management decisions that could potentially increase the survival of Green Sucker in the hatchery and improve the survival of Green Sucker after stocking into the wild. Ultimately the intent of this project is to provide information that will help conserve the important Weber River Green Sucker population.

The conservation of Green Sucker in the Weber River is identified in the rangewide 3 species Conservation Agreement and Strategy.

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Various thiamine deficiency experiments will be performed from summer 2024-summer 2026. Funding is being requested for the work in fiscal year 2025. Work performed afterwards will be funded by other sources. A total of four experiments are planned: 1) Egg Thiamine Concentration Comparisons, Summer 2024 -- Summer 2025 During the spawning season of 2024, UDWR biologists, along with a Utah State University M.S. student, will conduct streamside spawns and collect green eggs from wild Green Sucker from multiple sites, including but not limited to: the lower Weber River -- Section 2, upper Weber River, and Raft River. Raft River was chosen due to its relatively stable Green Sucker population and evidence of recruitment. Eggs will be flash frozen on dry ice for preservation and stored at -80º C until shipment to the USGS Columbia Environmental Research Center (CERC) for thiamine analysis via HPLC following protocols described in Futia and Rinchard (2019) and Reed et al. (2023). Habitat data will be collected at each location of Green Sucker capture to analyze in linear mixed-effects models as potential covariates predicting fry mortality in objective 2. Data will be compiled and analyzed with linear mixed-effects models for comparisons of thiamine level differences within each population and among the different populations. 2) Thiamine LC50 Curve, Summer 2024 -- Summer 2026 A portion of eggs collected from each female during methods described for objective 1 will be fertilized, hatched, and separately reared to 60 days post hatch at UDWR's Aquatic Animal Health and Research Center by the USU graduate student. Data on egg size, fry condition -- length and weight, TDC symptoms, and mortality will be collected on fry from individual females. Variability on these metrics will be used to develop LC50 (e.g., the threshold for egg thiamine concentration associated with 50% mortality of fry) for thiamine egg concentrations via three parameter logistic regression (Futia and Rinchard, 2019) using R package 'aomisc'. TDC comorbidities=(α)/(1+(egg thiamine conc /ꭓo)ᵇ) Where α = maximum asymptote, b = inflection point, and ꭓo = slope. An LC50 curve for thiamine will be developed and a minimum threshold will be identified for healthy Green Sucker development. 3)Thiamine Supplementation and Fry Survival, Summer 2024 -- Summer 2026 Half of the eggs from each female collected for Objective 2 will be treated with thiamine baths of varying concentrations and durations post-fertilization and reared separately from the non-treated eggs. Hatched fry mortality will be collected and compared between the treated and non-treated groups using a combination of linear mixed-effects models and three-parameter logistic regression models. This analysis will allow for the identification of effective thiamine bath treatment concentrations and/or durations. 4)Periphyton Thiaminase Concentration Comparisons, Summer 2024 -- Summer 2026 Periphyton samples will be collected from the multiple sites listed in objective 1. In collaboration with Freya Rowland at CERC, thiaminase analysis protocols will be developed and utilized to detect differences in thiaminase levels that might correlate with thiamine egg concentrations observed among the various Green Sucker populations sampled in objective 1. This data will be incorporated into the above mentioned linear mixed-effects models to assess its predictive significance for fry mortality studies conducted in objective 2.

The results from this study will be used to guide future management efforts. The efforts that are applied will be monitored by the UDWR Northern Region. Monitoring methodologies will be developed once the management recommendations of this study are selected and implemented.

Utah State University and the U.S. Geological Survey are partnering in this study and are waiving indirect costs and providing PI salary.

The results from this study will help direct future conservation efforts for Green Sucker in the Weber River.

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