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A multistressor study was conducted to investigate interactive effects of nutritional status and salinity on osmoregulation of juvenile white sturgeon. Our hypothesis was that lower nutritional status would decrease the salinity tolerance of juvenile white sturgeon. A four-week feed restriction (12.5%, 25%, 50%, 100% of optimum feeding rate: OFR defined as the rate (% body weight per day) at which growth is maximal) trial was performed, and relevant indices of nutritional status were measured. Following the trial, sturgeon were acutely exposed to various salinities (0, 8, 16, 24 ppt) for 120 h, and relevant osmoregulatory measurements were made at 12, 72, and 120 h post-salinity exposures. The feed-restriction trial resulted in a graded nutritional response with the most feed-restricted group (12.5% OFR) showing the lowest nutritional status. The salinity exposure trial showed clear evidence that lower nutritional status decreased the salinity tolerance of juvenile white sturgeon. Increasing salinities resulted in significant alterations in osmoregulatory indices of all feeding groups; however, a significantly slower acclimatory response to 24 ppt was detected in the most feed-restricted group compared to the non-feed-restricted group (100% OFR). Furthermore, evaluation of the effect of nutritional status on the relationship between osmoregulatory measurements and body size showed that there was a significant negative relationship between osmoregulatory performance and body size within the most feed-restricted group. This suggests that there is a certain body size range (200–300 g based on our finding) where juvenile white sturgeon can maximize osmoregulatory capacity at a salinity of 24 ppt. [ABSTRACT FROM AUTHOR]

Green and white sturgeon are species of high conservational and economic interest, particularly in the San Francisco Bay Delta (SFBD) for which significant climate change-derived alterations in salinity and nutritional patterns are forecasted. Although there is paucity of information, it is critical to test the network of biological responses underlying the capacity of animals to tolerate current environmental changes. Through nutrition and salinity challenges, climate change will likely have more physiological effect on young sturgeon stages, which in turn may affect growth performance. In this study, the two species were challenged in a multiple-factor experimental setting, first to levels of feeding rate, and then to salinity levels for different time periods. Data analysis included generalized additive models to select predictors of growth performance (measured by condition factor) among the environmental stressors considered and a suite of physiological variables. Using structural equation modeling, a path diagram is proposed to quantify the main linkages among nutrition status, salinity, osmoregulation variables, and growth performances. Three major trends were anticipated for the growth performance of green and white sturgeon in the juvenile stage in the SFBD: (i) a decrease in prey abundance will be highly detrimental for the growth of both species; (ii) an acute increase in salinity within the limits studied can be tolerated by both species but possibly the energy spent in osmoregulation may affect green sturgeon growth within the time window assessed; (iii) the mechanism of synergistic effects of nutrition and salinity changes will be more complex in green sturgeon, with condition factor responding nonlinearly to interactions of salinity and nutrition status or time of salinity exposure. Green sturgeon merits special scientific attention and conservation effort to offset the effects of feed restriction and salinity as key environmental stressors in the SFBD. [ABSTRACT FROM AUTHOR]

Abstract: Selenium (Se) and mercury (Hg) are prevalent pollutants of industrialized watersheds. However, when co-administered, Se has protective effects on organisms from Hg. The mechanism is not fully understood, but it is thought that Se reduces Hg availability, either by forming biologically inert complexes and/or associating with selenoproteins. Despite concerns with aquatic contaminations, relatively little information is available on the interaction in aquatic organisms. In the present study, the interactive effects of Se and Hg on their absorption, disposition, and elimination were examined in juvenile white sturgeon, a benthic fish species at high risk to exposures of both contaminants. Selenium and Hg were provided as l-selenomethionine (SeMet) and methylmercury (MeHg), respectively. Groups of 10 sturgeon were orally intubated with a single dose of either 0 (control), SeMet (500μg Se/kg body weight; BW), MeHg (850μg Hg/kg BW), or their combination (Se/Hg; 500μg Se/kg and 850μg Hg/kg BW). The blood was repeatedly sampled and urine collected from the fish, over a 48h post intubation period. At 48h, the fish were sacrificed for Se and Hg tissue concentration and distribution. The co-administration of SeMet and MeHg significantly (p <0.05) lowered blood concentrations of both Se and Hg and tissue Se concentrations. Similarly, assimilation of Se and Hg was also reduced significantly. The interaction has a more quantitative effect on Se metabolism because the reduction in the overall tissue Se is a consequence of reduced Se absorption at the gut and not from the metabolic effects after absorption. In contrast, given the pulse increase in blood Hg concentration, tissue redistribution, and increased urinary elimination, the interactive effect on tissue Hg concentration is likely to be post-absorption. Even in the absence of exogenous SeMet, Se and Hg co-accumulated in tissue at a Se:Hg molar ratio greater than 1. Thus, similar to mammals, maintaining at least a 1:1 molar ratio of Se and Hg is of great physiological importance in the white sturgeon. Interestingly, SeMet did not divert Hg from the brain. Allocation of Se from the kidneys may have occurred in order to maintain the high Se:Hg molar ratios in the brain of white sturgeon. In the current study, the combined use of kinetic analysis and that of the conventional approach of measuring tissue concentration changes provided a comprehensive understanding of the interactive effect of SeMet and MeHg on their respective metabolic processes in juvenile white sturgeon. [Copyright &y& Elsevier]

Abstract: Mercury (Hg) is toxic and is released into the environment from a wide variety of anthropogenic sources. Methylmercury (MeHg), a product of microbial methylation, enables rapid Hg bioaccumulation and biomagnification in the biota. Methylmercury is sequestered and made available to the rest of the biota through the benthic–detrital component leading to the high risk of exposure to benthic fish species, such as white sturgeon (Acipenser transmontanus). In the present study, a combined technique of stomach intubation, dorsal aorta cannulation, and urinary catheterization was utilized to characterize the absorption, distribution, and elimination of Hg in white sturgeon over a 48h exposure. Mercury, as methylmercury chloride, at either 0, 250, 500, or 1000μgHg/kg body weight, was orally intubated into white sturgeon, in groups of five. The blood was repeatedly sampled and urine collected from the fish over the 48h post intubation period, and at 48h, the fish were sacrificed for Hg tissue concentration and distribution determinations. The fractional rate of absorption (K), blood Hg concentration (μg/ml), tissue concentration (μg/g dry weight) and distribution (%), and urinary Hg elimination flux (μg/kg/h) are significantly different (p <0.05) among the MeHg doses. Complete blood uptake of Hg was observed in all MeHg treated fish by 12h. The maximal observed blood Hg concentration peaks are 0.56±0.02, 0.70±0.02, and 2.19±0.07μg/ml (mean±SEM) for the 250, 500, and 1000μgHg/kg body weight dose groups, respectively. Changes in blood Hg profiles can be described by a monomolecular function in all of the MeHg treated fish. The Hg concentration asymptote (A) and K are dose dependent. The relationship between A and the intubation dose, however, is nonlinear. Mercury levels in certain tissues are comparable to field data and longer-term study, indicating that the lower doses used in the current study are ecologically relevant for the species. Tissue Hg concentrations are in the following decreasing order: gastro-intestinal tract>kidney>spleen>gill>heart>liver>brain>white muscle and remaining whole body. At 48h, Hg was found to be preferentially distributed to metabolically active tissues. Digestibility is highest at the lowest MeHg dose. Measurable urinary Hg was observed in the fish treated with the highest MeHg dose, and a significant increase in the elimination flux was observed between 3 and 12h post intubation. [Copyright &y& Elsevier]

Establishing the optimum feeding rate (OFR; % body weight per day) for a cultured fish is a significant step toward the success of the aquaculture operation. Therefore, the objectives of this study were 1) the estimation of OFR for 19 datasets with different initial body weights by applying broken-line and quadratic regression models and 2) an investigation of potential OFR prediction models using 19 estimated OFRs from objective 1. Objective 1) Nineteen datasets were obtained from five published studies (14 datasets) and one unpublished study (5 datasets) which were carried out to evaluate the effects of feeding rate on growth performance in white sturgeon of initial body weights varying from 0.05 g to 764 g. Each dataset, containing feeding rate (independent variable) and specific growth rate (% body weight increase per day; dependent variable) was used to estimate OFR by one-slope straight broken-line, two-slope straight broken-line, quadratic broken-line, and quadratic models for each body weight class. Calculations of model selection criteria, including the adjusted coefficient of correlation, Akaike information criterion, and corrected Akaike information criterion were performed to compare model performance on OFR estimation for each dataset. Three models (two-slope straight broken-line, quadratic broken-line, and quadratic models) were considered acceptable for the estimation of OFR, and the three sets of estimated OFRs obtained by these models were used in objective 2. Objective 2) Several regression models, including polynomial models of order from 1 to 6, a simple exponential model with a constant, and a bi-exponential model, were fitted to each set of the 19 estimated OFRs against transformed initial body weights. A power function model was also fitted to the estimated OFRs against untransformed initial body weights. The model selection criteria for objective 2 were the same as those for objective 1. Overall model performance on the estimation of OFR for the 19 datasets shows that the quadratic broken-line model performed best, followed by the quadratic, two-slope straight broken-line, and one-slope straight broken-line models. Given the overall performance of model fitness to the sets of the OFR estimates, the bi-exponential regression model emerged as the most favorable one. As a result, the bi-exponential model equation. OFR % body weight per day = 0.00344 ± 0.0123 e − 5.684 ± 2.309 ln ( body weight ) + 8.695 ± 0.606 e − 0.549 ± 0.065 ln ( body weight ) obtained by fitting the estimated OFRs derived from the quadratic broken-line model analysis, can be used to predict the OFR for white sturgeon from about 0.05 g to 800 g. [ABSTRACT FROM AUTHOR]

Abstract: The biological function of selenium (Se) is determined by its form and concentration. Selenium is an essential micronutrient for all vertebrates, however, at environmental levels, it is a potent toxin. In the San Francisco Bay-Delta, Se pollution threatens top predatory fish, including white sturgeon. A multi-compartmental Bayesian hierarchical model was developed to estimate the fractional rates of absorption, disposition, and elimination of selenocompounds, in white sturgeon, from tissue measurements obtained in a previous study (). This modeling methodology allows for a population based approach to estimate kinetic physiological parameters in white sturgeon. Briefly, thirty juvenile white sturgeon (five per treatment) were orally intubated with a control (no selenium) or a single dose of Se (500μgSe/kgbody weight) in the form of one inorganic (Selenite) or four organic selenocompounds: selenocystine (SeCys), l-selenomethionine (SeMet), Se-methylseleno-l-cysteine (MSeCys), or selenoyeast (SeYeast). Blood and urine Se were measured at intervals throughout the 48h post intubation period and eight tissues were sampled at 48h. The model is composed of four state variables, conceptually the gut (Q 1), blood (Q 2), and tissue (Q 3); and urine (Q 0), all in units of μgSe. Six kinetics parameters were estimated: the fractional rates [1/h] of absorption, tissue disposition, tissue release, and urinary elimination (k 12, k 23, k 32, and k 20), the proportion of the absorbed dose eliminated through the urine (f 20), and the distribution blood volume (V; percent body weight, BW). The parameter k 12 was higher in sturgeon given the organic Se forms, in the descending order of MSeCys>SeMet>SeCys>Selenite>SeYeast. The parameters k 23 and k 32 followed similar patterns, and f 20 was lowest in fish given MSeCys. Selenium form did not affect k 20 or V. The parameter differences observed can be attributed to the different mechanisms of transmucosal transport, metabolic reduction, and storage of the Se forms, which, in general, appear to be similar to that in mammals. We have demonstrated that the Bayesian approach is a powerful tool for integrating quantitative information from a study with sparse blood and urinary measurements and tissue concentrations from a single time point, while providing a full characterization of parameter variability. The model permits the quantitative mechanistic interpretation and predictions of Se absorption, disposition, and elimination processes. Furthermore, the model represents a first step towards population based physiological toxicokinetic modeling of Se in white sturgeon. [Copyright &y& Elsevier]

Abstract: Selenium (Se) is an essential micronutrient for all vertebrates, however, at environmental relevant levels, it is a potent toxin. In the San Francisco Bay-Delta, white sturgeon, an ancient Chondrostean fish of high ecological and economic value, is at risk to Se exposure. The present study is the first to examine the uptake, distribution, and excretion of various selenocompounds in white sturgeon. A combined technique of stomach intubation, dorsal aorta cannulation, and urinary catheterization was utilized, in this study, to characterize the short-term effects of Se in the forms of sodium-selenate (Selenate), sodium-selenite (Selenite), selenocystine (SeCys), l-selenomethionine (SeMet), Se-methylseleno-l-cysteine (MSeCys), and selenoyeast (SeYeast). An ecologically relevant dose of Se (∼500μg/kg body weight) was intubated into groups of 5 juvenile white sturgeon. Blood and urine samples were repeatedly collected over the 48h post intubation period and fish were sacrificed for Se tissue concentration and distribution at 48h. The tissue concentration and distribution, blood concentrations, and urinary elimination of Se significantly differ (p ≤0.05) among forms. In general, organic selenocompounds maintain higher blood concentrations, with SeMeCys maintaining the highest area under the curve (66.3±8.7 and 9.3±1.0μgh/ml) and maximum Se concentration in blood (2.3±0.2 and 0.4±0.2μg/ml) in both the protein and non-protein bound fractions, respectively. Selenate, however, did not result in significant increase of Se concentration, compared with the control, in the protein-bound blood fraction. Regardless of source, Se is preferentially distributed into metabolically active tissues, with the SeMet treated fish achieving the highest concentration in most tissues. In contrast, Selenite has very similar blood concentrations and tissue distribution profile to SeCys and SeYeast. From blood and tissue Se concentrations, Selenate is not stored in blood, but taken up rapidly by the liver and white muscle. Urinary elimination of Se is form dependent and peaks between 3 and 12h post intubation. A basic understanding of the overall Se absorption, distribution, and elimination is provided through monitoring tissue Se concentrations, however, conclusions regarding to the dynamics and the specific processes of Se metabolism can only be inferred, in the absence of kinetic information. [Copyright &y& Elsevier]