Search

The internal organs of white sturgeon in Miyazaki Prefecture are discarded during processing. Therefore, we tried to produce fish sauce using a short-term manufacturing method. The minced internal organs were autolyzed by endogenous proteases at 50 °C. During autolysis, the protein contents of the supernatant and precipitate after centrifugation were analyzed by the Kjeldahl method, and the protein size was monitored by SDS-PAGE. This analysis showed that the extraction rate was about 60% after treatment at 50 °C for 24 h. The major bands at 200 kDa, 43 kDa, and 40 kDa detected before the start of the treatment gradually disappeared over time. Fifteen components were detected as the main volatile components. These components increased sharply and then decreased during incubation at 50 °C for 24 h. The fish sauce produced had a good aroma after incubation at 50 °C for 72 h.

Preferentially regulating intracellular pH (pH i ) confers exceptional CO 2 tolerance on fish, but is often associated with reductions in extracellular pH (pH e ) compensation. It is unknown whether these reductions are due to intrinsically lower capacities for pH e compensation, hypercarbia-induced reductions in water pH or other factors. To test how water pH affects capacities and strategies for pH compensation, we exposed the CO 2 -tolerant fish Pangasianodon hypophthalmus to 3 kPa P CO 2 for 20 h at an ecologically relevant water pH of 4.5 or 5.8. Brain, heart and liver pH i was preferentially regulated in both treatments. However, blood pH e compensation was severely reduced at water pH 4.5 but not 5.8. This suggests that low water pH limits acute pH e but not pH i compensation in fishes preferentially regulating pH i . Hypercarbia-induced reductions in water pH might therefore underlie the unexplained reductions to pH e compensation in fishes preferentially regulating pH i , and may increase selection for preferential pH i regulation.

Pre-print The effect of substrate on growth and metabolic rate was assessed in larval white sturgeon (Aciperser transmontanus). Yolk sac larvae (YSL) were reared in bare tanks or tanks with gravel as substrate from hatch until approximately 16 days post hatch (dph). The effect of an artificial substrate was also evaluated for growth alone. Substrate had a significant effect on weight, with larvae reared in gravel and artificial substrate being larger than those reared without substrate. Respirometry measurements of resting (routine) metabolic rates in fish reared without gravel were significantly greater than those reared with gravel during the yolk sac phase. Aerobic scope (the difference between maximum and routine metabolic rate) was significantly lower for YSL and feeding larvae (FL) in bare tanks than those reared with gravel, particularly before fish started feeding exogenously. Routine factorial scope (maximum metabolic rate divided by routine metabolic rate) indicated that the ability to elevate metabolic rate above routine in the early ontogeny of white sturgeon is extremely limited (< 1.7). These findings suggest that YSL reared without substrate may divert more of their energy to non-growth related processes, such as exercise, as higher activity levels were observed but not quantified in YSL sturgeon reared without substrate. These results underscore the importance of adequate rearing substrate for growth and development, and may provide support for habitat restoration and alternative hatchery rearing methods. Pre-print version This is the pre-peer reviewed version of the following article: Boucher, M.A., Baker, D.W., Brauner, C.J., & Shrimpton, J.M. (2018). The effect of substrate rearing on growth, aerobic scope, and physiology of larval white sturgeon Acipenser tranmontanus. Journal of Fish Biology. DOI: 10.1111/jfb.13611, which has been published in final form at https://doi.org/10.1111/jfb.13611. This article may be used for noncommercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. https://viurrspace.ca/bitstream/handle/10613/6054/Baker.JFB.pdf?sequence=3

The acute toxicity of cadmium, copper, and zinc to white sturgeon (Acipenser transmontanus) and rainbow trout (Oncorhynchus mykiss) were determined for 7 developmental life stages in flow-through water-only exposures. Metal toxicity varied by species and by life stage. Rainbow trout were more sensitive to cadmium than white sturgeon across all life stages, with median effect concentrations (hardness-normalized EC50s) ranging from 1.47 µg Cd/L to 2.62 µg Cd/L with sensitivity remaining consistent during later stages of development. Rainbow trout at 46 d posthatch (dph) ranked at the 2nd percentile of a compiled database for Cd species sensitivity distribution with an EC50 of 1.46 µg Cd/L and 72 dph sturgeon ranked at the 19th percentile (EC50 of 3.02 µg Cd/L). White sturgeon were more sensitive to copper than rainbow trout in 5 of the 7 life stages tested with biotic ligand model (BLM)-normalized EC50s ranging from 1.51 µg Cu/L to 21.9 µg Cu/L. In turn, rainbow trout at 74 dph and 95 dph were more sensitive to copper than white sturgeon at 72 dph and 89 dph, indicating sturgeon become more tolerant in older life stages, whereas older trout become more sensitive to copper exposure. White sturgeon at 2 dph, 16 dph, and 30 dph ranked in the lower percentiles of a compiled database for copper species sensitivity distribution, ranking at the 3rd (2 dph), 5th (16 dph), and 10th (30 dph) percentiles. White sturgeon were more sensitive to zinc than rainbow trout for 1 out of 7 life stages tested (2 dph with an biotic ligand model–normalized EC50 of 209 µg Zn/L) and ranked in the 1st percentile of a compiled database for zinc species sensitivity distribution. Environ Toxicol Chem 2014;33:2259–2272. © 2014. The Authors. This article is a US government work and, as such, is in the public domain in the United States of America. Environmental Toxicology and Chemistry published byWiley Periodicals, Inc. on behalf of SETAC. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Elevated carbon dioxide concentrations reduce feed intake and growth in several fish species and induce stress responses. In this study, the effects of moderately elevated CO2 levels on performance, energy partitioning, swimming activity and stress response in European seabass were assessed. European seabass (140.0 g) were reared under two levels of CO2 (1.6 and 7.0 mg L-1) and two feeding levels (FLs) (maintenance and satiation) for 60 days, and fish swimming speed was recorded. At the end of the experiment, fish were subjected to an acute stress test. Blood cortisol, glucose and lactate were analysed. Energy and nitrogen balances were quantified based on measurements of body composition and digestibility coefficients. Moderately elevated chronic CO2 level did neither affect energy requirements for maintenance nor the utilization of digestible energy for growth. However, swimming activity data suggests that FL dependent alterations in energy partitioning took place. Blood cortisol values after the acute stress were affected by additional CO2 exposure and this effect was also dependent on FL. The elevated CO2 exposure of 7.0 mg L-1 appears to act as a chronic stressor as adaptive responses took place, however, this CO2 exposure seems to be still within the allostatic load of the fish.

Simulated angling stress caused a physiological disturbance and reflex impairment in sub-adult/adult white sturgeon. Ventilation was the first reflex to become compromised, followed by orientation, mouth extension, tail grab and body flex. Reflex impairment indicated a compromised physiological state which correlated with the degree of the stressor (i.e. severity). Higher reflex impairment scores correlated with longer recovery times. Compromised physiological state was significantly higher in summer than winter treated fish. Two mortalities occurred >24 hours after the cessation of the stressor during the summer. Both individuals had all reflexes impaired upon release into the recovery tank, excess stress metabolites (i.e. lactate), and were ‘unrecovered’ following the 30 min. observation period post-release., White sturgeon (Acipenser transmontanus) are the largest freshwater fish in North America and a species exposed to widespread fishing pressure. Despite the growing interest in recreational fishing for white sturgeon, little is known about the sublethal and lethal impacts of angling on released sturgeon. In summer (July 2014, mean water temperature 15.3°C) and winter (February 2015, mean water temperature 6.6°C), captive white sturgeon (n = 48) were exposed to a combination of exercise and air exposure as a method of simulating an angling event. After the stressor, sturgeon were assessed for a physiological stress response, and reflex impairments were quantified to determine overall fish vitality (i.e. capacity for survival). A physiological stress response occurred in all sturgeon exposed to a fishing-related stressor, with the magnitude of the response correlated with the duration of the stressor. Moreover, the stress from exercise was more pronounced in summer, leading to higher reflex impairment scores (mean ± SEM, 0.44 ± 0.07 and 0.25 ± 0.05 in summer and winter, respectively). Reflex impairment was also correlated with lactate concentrations (e.g. physiological stress measures related to exhaustive exercise; r = 0.53) and recovery time (r = 0.76). Two mortalities occurred >24 h after the cessation of treatment in the summer. Given that natural habitats for white sturgeon can reach much higher temperatures than those presented in our study, we caution the use of this mortality estimate for a summer season, because latent mortality could be much higher when temperatures exceed 16°C. This is the first experiment investigating the physiological disturbance and reflex impairment of capture and release at two temperatures on subadult/adult white sturgeon, and the results suggest that future research needs to examine the longer term and fitness consequences of extended play and air exposure times, because these are largely unknown for wild populations.

Behavioral responses of aquatic organisms to environmental contaminants can be precursors of other effects such as survival, growth, or reproduction. However, these responses may be subtle, and measurement can be challenging. Using juvenile white sturgeon (Acipenser transmontanus) with copper exposures, this paper illustrates techniques used for quantifying behavioral responses using computer assisted video and digital image analysis. In previous studies severe impairments in swimming behavior were observed among early life stage white sturgeon during acute and chronic exposures to copper. Sturgeon behavior was rapidly impaired and to the extent that survival in the field would be jeopardized, as fish would be swept downstream, or readily captured by predators. The objectives of this investigation were to illustrate protocols to quantify swimming activity during a series of acute copper exposures to determine time to effect during early lifestage development, and to understand the significance of these responses relative to survival of these vulnerable early lifestage fish. With mortality being on a time continuum, determining when copper first affects swimming ability helps us to understand the implications for population level effects. The techniques used are readily adaptable to experimental designs with other organisms and stressors.

Migratory fishes encounter a variety of environmental conditions, including changes in salinity, temperature and dissolved gases, and it is important to understand how these fishes are able to acclimate to multiple environmental stressors. The gill is the primary site of both acid–base balance and ion regulation in fishes. Many ion transport mechanisms involved with acid–base compensation are also required for the regulation of plasma Na+ and Cl+, the predominant extracellular ions, potentially resulting in a strong interaction between ionoregulation and acid–base regulation. The present study examined the physiological interaction of elevated dissolved CO2 (an acid–base disturbance) on osmoregulation during seawater acclimation (an ionoregulatory disturbance) in juvenile white sturgeon (Acipenser transmontanus). Blood pH (pHe), plasma [HCO3−], [Na+], [Cl−] and osmolality, white muscle water content, and gill Na+/K+-ATPase (NKA) and Na+/K+/2Cl− co-transporter (NKCC) abundance were examined over a 10 day seawater (SW) acclimation period under normocarbia (NCSW) or during prior and continued exposure to hypercarbia (HCSW), and compared with a normocarbic freshwater (NCFW) control. Hypercarbia induced a severe extracellular acidosis (from pH 7.65 to pH 7.2) in HCSW sturgeon, and these fish had a 2-fold greater rise in plasma osmolarity over NCSW by day 2 of SW exposure. Interestingly, pHe recovery in HCSW was associated more prominently with an elevation in plasma Na+ prior to osmotic recovery and more prominently with a reduction in plasma Cl− following osmotic recovery, indicating a biphasic response as the requirements of osmoregulation transitioned from ion-uptake to ion-excretion throughout SW acclimation. These results imply a prioritization of osmoregulatory recovery over acid–base recovery in this period of combined exposure to acid–base and ionoregulatory disturbances. This study was funded by a University Research Council Research Grant and College of Science and Health Faculty Summer Research Grant from DePaul University to J.S.B., a Sigma Xi Grant-in-Aid of Research from the National Academy of Sciences to C.A.S., VIU research funds to J.D.M. and D.W.B., and a Natural Sciences and Engineering Research Council (NSERC) Discovery Grant and Accelerator Supplement to C.J.B. C.A.S. was supported by a Company of Biologists Journal of Experimental Biology Travelling Fellowship. This is an electronic version of an article that was published as: Shaughnessy, C.A., Baker, D.W., Brauner, C.J., Morgan, J.D., & Bystriansky, J.S. (2015). Interaction of osmoregulatory and acidbase compensation in white sturgeon (Acipenser transmontanus) during exposure to aquatic hypercarbia and elevated salinity. The Journal of Experimental Biology, 218(17), 2712-2719. DOI: 10.1242/jeb.125567 The Journal of Experimental Biology is published by The Company of Biologists. More information about the journal can be found at: http://jeb.biologists.org/. This article can be accessed at: http://dx.doi.org/10.1242/jeb.125567.

Techniques were developed to determine when fish are vulnerable to barotrauma when rapidly decompressed during hydroturbine passage. Sturgeons were decompressed in early life-stages and X-ray radiographs were taken to determine when gas was present in the swim bladder. Barotrauma was observed on day 9 and greater than 75 days after hatching., Techniques were developed to determine which life stages of fish are vulnerable to barotrauma from expansion of internal gases during decompression. Eggs, larvae, and juvenile hatchery-reared white sturgeon (Acipenser transmontanus; up to 91 days post hatch; d.p.h.) were decompressed to assess vulnerability to barotrauma and identify initial swim bladder inflation. Barotrauma-related injury and mortality were first observed 9 d.p.h., on the same day as initial exogenous feeding. However, barotrauma-related injury did not occur again until swim bladder inflation 75 d.p.h. (visible at necropsy and on radiographs). Swim bladder inflation was not consistent among individuals, with only 44% being inflated 91 d.p.h. Additionally, swim bladder inflation did not appear to be size dependent among fish ranging in total length from 61 to 153 mm at 91 d.p.h. The use of a combination of decompression tests and radiography was validated as a method to determine initial swim bladder inflation and vulnerability to barotrauma. Extending these techniques to other species and life-history stages would help to determine the susceptibility of fish to hydro turbine passage and aid in fish conservation.

Vitellogenin (Vg), the estrogen inducible protein precursor to egg yolk, serves as an indicator of exposure to estrogen mimicking environmental contaminants. Vg was isolated by size exclusion and ion exchange chromatography from plasma of California halibut (Paralichthys californicus) treated with estrogen. MALDI TOF mass spectrometry (MS) analysis resulted in a molecular mass of 188 kDa. MS/MS de novo sequencing provided evidence that California halibut has more than one form of Vg. Similar analysis on white sturgeon (Acipenser transmontamus) Vg did not reveal adequate evidence to suggest that sturgeon has more than one Vg. The potential of using other MS methods to understand the structure and function of Vg are discussed. An ELISA for measurement of California halibut plasma Vg was optimized and validated using a commercially available antibody developed for another flatfish species, turbot. Inclusion of overnight preincubation was critical for low detection limits. Increasing the amount of Tween-20 to 0.05% in buffers was most effective for improving recoveries of spiked plasma samples. At the IC50, the average recovery of spiked plasma samples was 104% and the interplate CV was 12%. The working range of the assay was 33-1000 ng/mL, while the detection limit in a plasma sample is 2.2 µg/mL. The response to the model compounds 17beta-estradiol and/j-nonylphenol show that this is a suitable model for further studies of estrogen mimicking contaminants. White sturgeon are native to the Sacramento River and subject to agricultural, municipal and industrial waste water effluents that likely contain different classes of endocrine-disrupting contaminants. Reductions in 17beta-estradiol-induced vitellogenin levels were observed in white sturgeon co-injected with beta-naphthoflavone (BNF, 50 mg/kg), an Ah receptor agonist. The inhibition was maximal when the compounds were injected simultaneously versus prior treatment offish with BNF. This timing of the effect compared to increases in ethoxyresorufin-O-deethylase (EROD) activity suggests that the effect is not directly due to enhanced estrogen metabolism by the Ah receptor-induced enzymes. Results of this study will be relevant for those with monitoring programs who measure vitellogenin, as it is important to understand how Ah (dioxin) receptor active environmental contaminants can influence this endpoint.

An 8-week growth trial was conducted to determine the sensitivity of white sturgeon (Acipenser transmontanus) to the toxicological effects of elevated dietary selenium (Se). Juvenile white sturgeon were fed diets supplemented with Se in the form Of L-selenomethionine (SeMet), resulting in dietary concentrations of 0.4, 9.6, 20.5, 41.7, 89.8, and 191.1 mu g Se/g diet on a dry weight basis. Effects of dietary SeMet on survival, swimming activity, growth, whole-body proximate composition, tissue Se concentrations, and histopathology were determined. Sturgeon survival among treatment groups did not differ significantly with a mean survival rate of 99 +/- 0.43% across all groups. A significant decrease (p < 0.05) in swimming activity and growth rate was observed in sturgeon fed at or above 41.7 mu g Se/g diet. Dietary SeMet concentrations were negatively correlated with whole-body protein and lipid content, but positively correlated with ash and moisture content. Selenium accumulated. in the kidney, muscle, liver, gill, and plasma tissues in a dose-dependent manner. Histopathological alterations in the liver and kidney were observed in sturgeon fed above 20.5 mu g Se/g diet. The threshold dietary Se toxicity concentration for white sturgeon was estimated to lie between 10 and 20 jig Se/g diet based on the histopathological alterations in the kidney. Research examining the consequences of elevated dietary Se concentrations on more sensitive life stages and the interactive effects of Se with other chemical or physical stressors are needed in order to determine if dietary threshold should be lowered to minimize the potential impacts of Se on white sturgeon in the San Francisco Bay-Delta. (c) 2006 Elsevier B.V. All rights reserved.

This study sought to determine whether wild white sturgeon from the Columbia River (Oregon) were exhibiting signs of reproductive endocrine disruption. Fish were sampled in the free-flowing portion of the river (where the population is experiencing reproductive success) and from three reservoirs behind hydroelectric dams (where fish have reduced reproductive success). All of the 18 pesticides and almost all of the 28 polychlorinated biphenyls (PCBs) that were analyzed in livers and gonads were detected in at least some of the tissue samples. Metabolites of p,p′-dichlorodiphenyltrichloroethane (DDT) [p,p′-dichlorodiphenyldichloroethylene (DDE) and p,p′-1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (DDD)] were consistently found at relatively high levels in fish. Some males and immature females showed elevated plasma vitellogenin; however, concentrations were not correlated with any of the pesticides or PCBs analyzed. Negative correlations were found between a number of physiologic parameters and tissue burdens of toxicants. Plasma triglycerides and condition factor were negatively correlated with total DDT (DDD + DDE + DDT), total pesticides (all pesticides detected – total DDT), and PCBs. In males, plasma androgens and gonad size were negatively correlated with total DDT, total pesticides, and PCBs. Fish residing in the reservoir behind the oldest dam had the highest contaminant loads and incidence of gonadal abnormalities, and the lowest triglycerides, condition factor, gonad size, and plasma androgens. These data suggest that endocrine-disrupting chemicals may be accumulating behind dams over time. Overall, results of this study indicate that exposure to environmental contaminants may be affecting both growth and reproductive physiology of sturgeon in some areas of the Columbia River.

An 8-week growth trial was conducted to study carbohydrate utilization by white sturgeon fed diets containing glucose or hydrolyzed potato starch (HPS). Four diets supplemented with 15% or 30% of glucose or HPS and a control diet with no added carbohydrate were each fed to triplicate groups of fish. The diets were processed by a 3-min 80 degrees C microwave moist heating, followed by 1-h 70 degrees C drying. Feeding rates varied from 1.7% to 3.2% body weight day(-1) so that all treatment groups were fed the same amount of dietary protein and lipid. The HPS groups showed the highest (P

Genetics professor Dr. Bernie May of the University of California at Davis and Sea Grant Trainee Dr. Jeff Rodzen were funded to develop a breeding program for broodstock at Stolt Sea Farm, the state’s largest producer of white sturgeon caviar. The goal of the project was twofold: to develop a breeding plan for slowing the rate of inbreeding of offspring and to investigate whether commercially desirable traits—superior growth rates, enhanced caviar yield and early sexual maturity—can be selectively bred.

The overall intent of this project was to develop a breeding plan for white sturgeon, using Stolt Sea Farm California LLC as a model system for broodstock management and selection using molecular markers. While the title of this project implies the function of the breeding plan to be of maintaining existing genetic variation as inferred from nuclear DNA markers, it is in the best interest of those parties involved in commercial production of this species to evaluate the feasibility of directed selection for economic traits such as growth rate. Thus, this project involves the estimation of quantitative genetic variation in addition to developing specific applications of molecular markers to broodstock management. Recommendations for their integration into a breeding plan and an overview of our research will be summarized in a manuscript being prepared (Rodzen et al. in prep4).

Nine tetramer [GATA]n microsatellite systems were developed for use in the white sturgeon, Acipenser transmontanus. We report inheritance patterns for these nine systems, which range from one possible disornic system to tetrasomy and octosomy, with some systems containing null alleles. Due to the complex modes of inheritance underlying these systems and the highly duplicated nature of the genome, we propose each allele be scored as its own dominant marker, similar to AFLPs or RAPDs. The utility of this method is validated by the observation that individual alleles within a microsatellite system generally fit the expectation for independent transmission and fit the expected transmission frequency for single copy nuclear markers.

I have developed a technique to determine the sex of live adult sturgeons by examination of external morphology. I analyzed four North American sturgeon species: 'Acipenser transmontanus' (white sturgeon), ' A. oxyrhincus' (Atlantic sturgeon), 'A. medirostris' (green sturgeon) and 'A. brevirostrum' (shortnose sturgeon). The opening of the urogenital duct is posterior to the anus. Males have a urogenital opening with a capital Y-shape while females have an O-shaped opening. Accuracy of sex determination was highest in live fish (82%), but significantly lower in dead fish (29%). Dead sturgeon usually have the rectum prolapsed via the cloaca so the urogenital opening and surrounding fleshy tissue are protruded, thus making the sexes indistinguishable. I tested this technique with nai?ve field personnel and observers in the laboratory. Successful application of this technique requires training of both those taking observations on the fish and those interpreting resulting photographs.

Significant progress has been achieved during the past several years in understanding endocrine control of reproduction in white sturgeon, Acipenser transmontanus (Moberg et al., 1995; Doroshov et al., 1997), however the regulation of prespawning oocyte development and the effects of environmental factors on this phase have been inadequately studied. Field and experimental observations suggest that the thermal regime of rivers plays a pivotal role in environmental control of tinal ovarian maturation (FOM) and spawning of wild sturgeon (Dettlaff et al., 1993), and constant, elevated temperatures have been found to result in decreased plasma sex steroid concentrations, a high incidence of ovarian atresia, and spawning failure in cultured sturgeon (Webb et al., 1999). Chapter l reviews our current knowledge of sturgeon reproductive endocrinology and the effects of environmental factors, specifically temperature, on the late phase of oogenesis. The effects of environmental temperature, ultimately mediated y brain-pituitary secretions, can be tested at the level of the ovary by observations on sex steroid secretion correlated with oocyte development. The objectives of this project were l) to determine baseline steroidogenic profiles in prespawning female sturgeon exposed to seasonal temperature, 2) to identify native steroid hormones involved in oocyte maturation, and 3) to examine and compare ovarian development, acquisition of maturational competence, and plasma sex steroid profiles in gravid females reared in warm water and transferred to cold water in the late fall or early spring. Chapter 2 characterizes the baseline plasma steroid profile and in vitro ovarian steroid secretion in two females held at seasonal temperatures throughout FOM and ovulation. Ovarian follicles were incubated with or without pregnenolone (P5), and concentrations of testosterone (T), 11-ketotestosterone (KT), estradiol (E2), and 17a, 208-dihydroxy-4-pregnen-3-one (17, 208-P) were measured by radioimmunoassay in the incubation media. The follicles of both females reached maturational competence (the ability to undergo germinal vesicle breakdown, GVBD, in response to a progestin in vitro), and ovulation was induced by hormonal treatment. Female 1 responded with oocyte maturation (GVBD), but did not ovulate. Female 2 underwent the normal sequence of oocyte maturation and ovulation. Lower in vitro production of T, KT, and 17, 208-P and elevated E2 were detected in Female 1 compared to Female 2. A surge in plasma 17, 20B-P was found in Female 2 at the onset of oocyte maturation before ovulation. No such surge was detected in the plasma of Female 1. High performance liquid chromatography (HPLC) analysis of plasma at the actual or expected time of ovulation revealed several C21 steroids present in the plasma of Female 2 that were absent in Female 1 These results suggest that it may be possible to assess follicular health during FOM through plasma steroid concentrations or follicular steroidogenesis as a means to select females for hormonal induction of ovulation or estimate the spawning potential of wild females. The ovarian follicles collected from Females 1 and 2 after a priming injection with pituitary extracts were used to determine the putative maturation-inducing steroid (MIS) involved in GVBD (Chapter 3). Follicles were incubated in the presence of a radiolabelled precursor eH-P5). Steroids were extracted from media and intact follicles, and the extracts were analyzed and fractionated by HPLC. The fractions were used in a bioassay to determine the potency of the endogenous steroid products. The results revealed production of C 19 and C2l steroids by the ovarian follicles of primed females, and several of these steroids were found to be physiologically active in the induction of GVBD in oocytes collected from ripe sturgeon females. However, only two fractions, containing a steroid with the same isopolarity as the authentic steroid 11-deoxycortisol (S) on HPLC and a steroid positively identified as 17, 208-P (HPLC and gas chromatography-mass spectrometry), were found to stimulate the resumption of meiosis at the shortest time of oocyte incubation. These steroids, produced in large quantities in vitro by the follicles undergoing GVBD, may be potential putative MISs in white sturgeon. The in vitro effects of steroids on oocyte maturation in sturgeon were further investigated using synthetic hormones matching native C19 and C21 steroids produced in vitro during GVBD (Chapter 4). Ovarian follicles from four mature sturgeon females were incubated with the synthetic steroids at different concentrations and exposure times. At the highest concentration (>1 J.Lg/rnl), all of the C21 steroids tested (progesterone, P4; 17a­ hydroxyprogesterone, 170HP; 17a, 20B, 21-trihydroxy-4-pregnen-3-one, 20B-S; cortisol, F; 17, 20B-P, and S) and T induced maturation at 14 and 22 hrs. At 6 hrs, only P4 and 17, 20B-P induced maturation at the highest concentration. At 14 and 22 hrs, S was the most potent steroidal inducer of GVBD followed closely by P4 and 170HP. The C21 steroids induced oocyte maturation at lower concentrations compared to the C19 steroid T. Calculation of the mean effective concentration that induced 50% GVBD (EC50) revealed the following order of potencies: S > P4 > 170HP > 17, 20B-P > 20B-S >> F > T. These results, together with previous findings on the in vitro production of native steroids, indicate that more than one steroid has a biological role in the resumption of meiosis in sturgeon follicles and provides empirical evidence for S, 17. 20B-P, P4, and 170HP as the most potent steroid inducers of GVBD. The objective of Chapter 5 was to examine and compare ovarian development, acquisition of maturational competence, and plasma sex steroid profiles in gravid sturgeon females reared in warm water and transferred to cold water in the late fall or early spring. Eighteen gravid females that had been raised under natural photoperiod at water temperatures of 16-20°C were randomly assigned to two groups (n=6 in Group 1 and n=12 in Group 2). Group 1 was transferred from warm water to cold water (12±1°C) in November 1997, while Group 2 was held in ambient water temperatures (10-19°C). Both groups were sampled in March 1998. Half of the fish in Group 2 had regressed ovaries, but the remaining females (n=6) had intact ovarian follicles and were transported to the cold water one week after the sampling. Ovarian follicles and blood were collected from October 1997 to November 1998, and the reproductive development was monitored until each female reached the stage of spawning readiness (oocyte polarization index s 0.10 and ovarian follicles had acquired maturational competence in vitro) or until atretic follicles were detected. Chonic exposure of gravid sturgeon females to elevated water temperature from October to March led to a decrease in plasma sex steroids and a high incidence of ovarian atresia in 50% of the females. It appears that the temperature-sensitive phase in ovarian development occurs during the transition from vitellogenic growth to FOM. The degree and timing of sensitivity to environmental temperature in the broodstock population are dependent on the female endogenous rhythms. Normal ovarian development occurred in the majority (83%) of females with intact follicles transferred to cold water in the fall or early spring. Though holding gravid females in cold water has extended the spawning season, the majority of females in our study reached the stage of spawning readiness by June. Several females, however, did retain maturational competence until early fall. A decrease in plasma T and KT was evident five weeks to several months prior to visual signs of atresia indicating that aquaculturists and conservationists may be able to screen potential sturgeon spawners based on androgen concentrations. Understanding ovarian steroidogenesis during FOM and ovulation elucidates the hormonal regulation of late oogenesis in sturgeon and provides useful information for environmental studies in aquaculture and in the wild. For example, baseline plasma steroid data may be used in the analysis of normal and abnormal gonad function of fish exposed to adverse environmental conditions during spawning migrations or holding in captivity. Characterization of the temperature-sensitive stage in late oogenesis of sturgeon enables aquaculturists and conservationists to determine the best timing of exposure of maturing females to cool water and ensure that environmental temperature is not a limiting factor influencing follicular development and spawning of sturgeon.

Pre-print, The effect of substrate on growth and metabolic rate was assessed in larval white sturgeon (Aciperser transmontanus). Yolk sac larvae (YSL) were reared in bare tanks or tanks with gravel as substrate from hatch until approximately 16 days post hatch (dph). The effect of an artificial substrate was also evaluated for growth alone. Substrate had a significant effect on weight, with larvae reared in gravel and artificial substrate being larger than those reared without substrate. Respirometry measurements of resting (routine) metabolic rates in fish reared without gravel were significantly greater than those reared with gravel during the yolk sac phase. Aerobic scope (the difference between maximum and routine metabolic rate) was significantly lower for YSL and feeding larvae (FL) in bare tanks than those reared with gravel, particularly before fish started feeding exogenously. Routine factorial scope (maximum metabolic rate divided by routine metabolic rate) indicated that the ability to elevate metabolic rate above routine in the early ontogeny of white sturgeon is extremely limited (< 1.7). These findings suggest that YSL reared without substrate may divert more of their energy to non-growth related processes, such as exercise, as higher activity levels were observed but not quantified in YSL sturgeon reared without substrate. These results underscore the importance of adequate rearing substrate for growth and development, and may provide support for habitat restoration and alternative hatchery rearing methods., Pre-print version, This is the pre-peer reviewed version of the following article: Boucher, M.A., Baker, D.W., Brauner, C.J., & Shrimpton, J.M. (2018). The effect of substrate rearing on growth, aerobic scope, and physiology of larval white sturgeon Acipenser tranmontanus. Journal of Fish Biology. DOI: 10.1111/jfb.13611, which has been published in final form at https://doi.org/10.1111/jfb.13611. This article may be used for noncommercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving., https://viurrspace.ca/bitstream/handle/10613/6054/Baker.JFB.pdf?sequence=3