Juvenile Sturgeon Research Articles

Russian sturgeon cultured in a subtropical climate shows weaken innate defences and a chronic stress response

Russian sturgeon (Acipenser gueldenstaedtii) has been successfully farmed in Uruguay for the past ten years. However, during the Uruguayan summer fish endure high water temperatures and increased bacterial infections that threaten aquaculture. Our understanding of sturgeon's immune system and its interplay with environmental factors like temperature is almost unknown. This study analysed the way in which seasonal variations affect enzymatic blood components of Russian sturgeon's innate defences, including the serum alternative complement pathway (ACP), ceruloplasmin (Cp) and lysozyme activities. Results showed that summertime conditions in the farm altered these defences in different ways, inducing a significant decrease in ACP and Cp, and an increase in lysozyme. In addition, serum levels of total protein and cortisol decreased in summer, suggesting a chronic stress response was induced in parallel. Subsequently, we analysed whether the increase in water river temperature during summer could account for the observed results. To that end, we acclimated juvenile sturgeons to mild (18 °C) or warm (24 °C) temperatures for 37 days. Like in summer, sturgeons exposed to 24 °C showed lower levels of serum ACP, Cp and total proteins, together with a progressive decrease in body weight and increased fish mortality. Administration of an immunostimulant containing Se and Zn slightly reverted the temperature-induced effects on sturgeon's defences. Altogether, our study provides novel data on various physiological parameters of the Russian sturgeon and highlights the impact warm temperature has on stress and innate immunity in this chondrostean fish.

Prospects of studies on the yeast flora of sturgeons for monitoring of their state in aquaculture

Seasonal changes in abundance and species composition of the yeast flora from organs of juvenile sturgeons were traced during their growing in the warm-water ponds of Luchegorsk Research Station of the Pacific Fish. Res. Centre (TINRO) in 2008-2009. The fungal community of the sturgeons was represented by whey, brewers, and wine yeasts, mostly with probiotic properties. Naganishia albida, Papiliotrema laurentii, Saccharomyces cerevisiae, Trichomonascus ciferrii , and fungi of the genus Candida were found in the intestines and gills of kaluga and siberian sturgeon juveniles, but they came from the water and are usual for microflora of cages for fish cultivation. Cryptococcus neoformans and Ogataea angusta were found in the water only. Rhodotorula mucilaginosa , Cystobasidium minuta and fungi of the genus Hanseniaspora were associated with the sturgeon organs. Generally the yeast heterotrophic microbiota in the cages showed inhibitory effect against mould and enterobacteria. Colonization of the sturgeon mucous membranes by yeasts had seasonal dynamics that definitely affected on local immunity of the juveniles. Complete elimination of the yeasts from the sturgeon mucous membranes should be considered as a predictor of worsening of their physiological state and anti-epizootic measures are necessary in this case.

Stock assessment of juvenile sturgeons in the Iranian water of the Caspian Sea by bottom trawl survey

The sturgeon stock assessment was performed to aim at estimation of absolute and relative abundance and determination of species composition at lower 10 m depths using the Si-Sara2 RV vessel in the Iranian coasts of the Caspian Sea in Guilan, Mazandaran and Golestan provinces during 6-30 September 2011-2012. In this study, 40 stations were selected on the basis of stratified random sampling design and then the stock estimation was performed using the swept area method. The study was carried out using bottom trawling with 9 m head rope. The time and speed of trawling in each station were 30 minutes and 2.5 knots respectively. The Catch per Unit of Effort (CPUE) in 2011–2012 were 7.03 and 6.96 individuals per trawling, respectively. The catch per unit of area in these years were found to be 1662 and 1644 fish in nm2, respectively. Total abundance of sturgeon juveniles was 13,327,164 individuals in 2011. So, the species composition included A. persicus (87.8%) and A. stellatus (12.2%). Total abundance of sturgeon juveniles was found to be 14,364,882 individuals in 2012 and the species composition comprised A. persicus (61.4%) and A. stellatus (38.6%). In 2011 the biomass of sturgeons in Iranian coastal water of the Caspian Sea was 295 tons and the composition of biomass included A. persicus (81.5%) and A. stellatus (18.5%), respectively. In the cruises conducted in 2011, this amount was estimated to be 217 tons comprising A. persicus (54.2%) and A. stellatus (45.8%), respectively. The results of this study in 2011–2012 showed remarkable abundance of juvenile sturgeons in Iranian coastal waters of the Caspian Sea in late summer and early autumn. So, by conserving these valuable stocks, the number of spawners will be increased in the future.

СЕЗОННАЯ ДИНАМИКА МОРФОФИЗИОЛОГИЧЕСКИХ ПОКАЗАТЕЛЕЙ МОЛОДИ РУССКОГО ОСЕТРА В СВЯЗИ С РЕЖИМОМ КОРМЛЕНИЯ И СОСТАВОМ КОМБИКОРМОВ

The article presents the results of the accelerated recovery after loss of weight and physiological status after wintering, for example, Russian sturgeon ( Acipenser gueldenstaedtii , Brandt) juveniles aged 1+…2+ years in LLC "Fish farm "Aquatrade" (the Astrakhan Region). There was determined weight, length, fatness of fishes, content of hemoglobin, whey protein, lipids, cholesterol in blood, erythrocytes sedimentation rate at the age of 18 months (before wintering), 24 months (after wintering), 25 and 26 months (in the feeding process), 31 months (after recovering period). Before wintering the young was characterized by optimum physiological rates, after wintering (age 24 months) physiological state got worse; weight loss made 7-8%; fatness decreased from 0.48 ± 0.03 to 0.45 ± 0.4 units. At the first stage of the experiment after wintering the young was fed by compound feed "Aquarex 48/17" (higher content of lipids and protein, experiment) and "Aquarex 45/12" (standard recipe, control). Feed duration was not longer than 25 days. Growth rate of the young under experiment appeared higher that that under control: on average, weight of fishes aged 25 months made 600 ± 21.1 (experiment) and 560 ± 2.6 g (control). Further feed of the young aged before 26 months, and further up to 31 months with standard recipy feed both in experiment and in controll showed more intensive growth in the experimental group: at the end of experiment weight of fishes made 1064.5 ± 33.8 (experiment) and 727.2 ± 32.9 (control). Young physiological status greatly optimized. Short-term feeding of the sturgeon young after wintering with combined feed "Aquarex 48/17" shortens the period of recovering from losses of weight and physiological status to 5 days and shoprtens time and costs of growing commodity product.

Isolation and characterization of an atypical Siberian sturgeon herpesvirus strain in Russia: novel North American Acipenserid herpesvirus 2 strain in Europe?

Siberian sturgeon herpesvirus (SbSHV) was isolated in Russia for the first time in 2006. Nine SbSHV isolates were recovered from different fish hatcheries producing the same cytopathic effect in cell cultures, the same clinical signs and mortality kinetics in virus-infected fish and the same virus neutralization pattern and shared identical nucleotide sequences. In 2011, a new isolate was recovered from juvenile sturgeon, which caused completely different cytopathic effect. That isolate was not readily neutralized by Siberian sturgeon hyperimmune antisera, and its DNA was not recognized by the routine PCR developed for SbSHV detection. Molecular study of the novel isolate revealed that it was more closely related to North American Acipenserid herpesvirus 2 (AciHV-2) isolates from white sturgeon, while the genome sequences of the former SbSHV isolates showed high similarity to the AciHV-2 isolated from shortnose sturgeon. While clinical signs and mortality caused by the novel isolate in infected Siberian sturgeon were similar to those of the formerly described SbSHV isolates, the incubation period and mean time to death produced by the novel isolate were twice as long. The differences between the former isolates and the recent one suggest that a novel SbSHV strain emerged in Europe and the molecular findings imply its North American origin.

Dietary zinc requirement of Siberian sturgeon (Acipenser baerii, Brandt 1869) juveniles, based on the growth performance and blood parameters

This study investigated the effect of dietary Zn levels on growth performance, feed utilization, and hematological parameters of juvenile Siberian sturgeon (Acipenser baerii, Brandt 1869). The five semi-purified diets were formulated by adding 0, 5, 10, 20, and 40 mg Zn kg−1 diet in the form of zinc sulfate (ZnSO4) to provide the actual dietary value of 14.7, 20.8, 27.3, 37.7, and 46.4 Zn kg−1 diet, respectively. The results showed that dietary Zn elevating level significantly improved the growth and feed utilization of the fish (p < 0.05), but not the hepatosomatic index (p > 0.05). Erythrocyte number, hemoglobin concentration, and hematocrit were increased with raising dietary Zn level (p < 0.05), whereas a regular trend was not observed in blood indices, including MCV, MCH, and MCHC. A significant increase was also found in the leucocyte number followed by their differential counts, except for eosinophil percentage. The broken line regression model indicated optimal dietary Zn level for growth maximization of fish was estimated to be 29.15 mg Zn kg−1 diet. In spite of well correlation with dietary Zn level, no break point was observed to estimate the juvenile Siberian sturgeon requirement based on the erythrocyte numbers.

Comparative Studies of Several Physiologic and Biochemical Indexes of Wild Type and Hatchery-Bred Sturgeons in the Early Ontogenesis

It was shown that, depending on the ways of breeding and living conditions, realization of food-seeking and defensive behavioural reactions as well as single biochemical indexes (pattern of neurotransmitters and levels of free amino acids in the brain) in the wild type and hatchery-bred sturgeon juveniles differ significantly. Basing on the studied indexes, the juveniles, bred in the ponds, are close to the wild type juveniles, whereas the juveniles, bred by pool technique, are quite different from them.

Dispersal and survival of stocked juvenile hatchery-reared Atlantic sturgeon (Acipenser oxyrinchus)

Abstract The post-stocking dispersal of juvenile Atlantic sturgeon (Acipenser oxyrinchus Mitchill) in the Wis3oka River (southern Poland) was investigated using biotelemetry. Thirty-five hatchery-reared juvenile A. oxyrinchus were tagged with radio or acoustic transmitters and tracked using mobile surveys and fixed receivers. Daily movement patterns were similar in 2009 and 2010. The sturgeon migrated with a mean speed of 1.42 km h-1 in 2009 and of 2.06 km h-1 in 2010. Migration rate was not regarded as being dependent on juvenile sturgeon size. The confirmed survival of individuals from the two field seasons differed slightly over the course of this study. Short-term survival of A. oxyrinchus was 86.7 and 90% in 2009 and 2010, respectively.

A small long-life acoustic transmitter for studying the behavior of aquatic animals.

Acoustic telemetry is an important tool for studying the behavior of aquatic animals and assessing the environmental impact of structures such as hydropower facilities. However, the physical size, signal intensity, and service life of off-the-shelf transmitters are presently insufficient for monitoring certain species. In this study, we developed a small, long-life acoustic transmitter with an approximate length of 24.2 mm, diameter of 5.0 mm, and dry weight of 0.72 g. The transmitter generates a coded acoustic signal at 416.7 kHz with a selectable source level between 159 and 163 dB relative to 1 μPa at 1 m, allowing a theoretical detection range of up to 500 m. The expected operational lifetime is 1 yr at a pulse rate interval of 15 s. The new technology makes long-term acoustic telemetry studies of small fish possible, and is being deployed for a long-term tracking of juvenile sturgeon.

Physiological and molecular responses of juvenile shortnose sturgeon (Acipenser brevirostrum) to thermal stress

The shortnose sturgeon (Acipenser brevirostrum LeSueur, 1818) is a vulnerable species that is found along the eastern coast of North America. Little is known about temperature tolerance in this species and with a rapidly changing global climate, it becomes increasingly important to define the thermal tolerance of this species to better predict population distribution. Using a modified critical thermal maximum test (CTMax), the objectives of this study were to determine the impact of heating rate (0.1, 0.2 and 0.25°Cmin−1) on the thermal tolerance, associated hematological responses, and oxygen consumption in juvenile sturgeon. In addition, transcripts associated with physiological stress and heat shock (i.e., heat shock proteins) were also measured. Heating rate did not alter the CTMax values of shortnose sturgeon. Neither heating rate nor thermal stress affected plasma sodium and chloride levels, nor the expression of transcripts that included catalase, glucocorticoid receptor, heat shock protein70 (hsp70), heat shock protein 90α (hsp90α) and cytochrome P450 1a (cyp1a). However, regardless of heating rate, thermal stress increased both plasma potassium and lactate concentrations. Glucose levels were increased at heating rates of 0.2 and 0.25°Cmin−1, but not at 0.1°Cmin−1. Overall, oxygen consumption rates increased with thermal stress, but the response patterns were not affected by heating rate. These data support the hypothesis that shortnose sturgeon can tolerate acute heat stress, as many physiological and molecular parameters measured here were non-responsive to the thermal stress.

The physiology of juvenile shortnose sturgeon (Acipenserbrevirostrum) during an acute saltwater challenge

One-year-old shortnose sturgeons (Acipenser brevirostrum LeSueur, 1818) were exposed to seawater (32 ppt) and brackish water (16 and 24 ppt) for 12, 24, 48, and 72 h and % body mass loss, plasma ions, energy metabolites, and oxygen-carrying variables were measured to evaluate survival and the physiological response to the acute salinity challenges. Survival in seawater was poor and plasma ion concentration was elevated in seawater. In sturgeons exposed to 24 ppt brackish water, ion concentrations remained elevated for 48 h, but began to decrease by 72 h. Fish exposed to 16 ppt brackish water did not show significant changes in ion concentrations over the 72 h period. Exposure to 32 ppt seawater resulted in significant and large decreases in body mass (about 20%–25%), whereas body mass loss was significantly less in fish exposed to 16 and 24 ppt brackish water. Overall, these findings suggest that juvenile sturgeons are able to tolerate lower salinities well but are less capable to endure higher salinities even on the short term (&gt;48 h). These results suggest that juvenile A. brevirostrum could inhabit brackish environments earlier than previously expected, and that there appears to be a threshold at which salinity becomes a significant stress to these animals.

Reaction of osmoregulatory system in juveniles of Russian sturgeon Acipenser gueldenstaedtii (Acipenseridae) on influence of comatotropin of carp Cyprinus carpio

For the first time by the example of juveniles of Russian sturgeon Acipenser gueldenstaedtii Brandt, the role of growth hormone of hypophysis in the osmotic regulation of acipenserids was studied, also the process of transformation of reserve chloride was described. In Russian sturgeon juveniles, administration of growth hormone of carp Cyprinus carpio at a dose of 1 mg per 1 g body weight causes changes in the fine structure of numerous reserve (undifferentiated) gill epithelial cells and thus stimulates their transformation into mature chloride cells involved in transport of monovalent ions. Increase in the number of chloride cells, on account of reserve cells, was accompanied by higher enzymatic activity of Na+/K+-ATPase in gill homogenates of the injected fish adapting to a hyperosmotic environment of salinity 12.5‰ (403 mosm/l) than in the intact fish under the same conditions but without hormonal treatment. Morphophysiological changes observed in the injected juveniles provided the more efficient dynamics of blood serum osmolarity under saline exposure than that in the intact fish. Their serum osmolality during the maximum rise (24 hours after the transfer of fish into the water of 12.5‰ salinity) was lower (p <0.01), than that of the intact fish. The inclusion of growth hormone in the osmoregulatory process was established.

Features of the effect of a complex probiotic with Bacillus bacteria and the larvae of Hermetia illucens biomass on Mozambique tilapia (Oreochromis mossambicus × O. niloticus) and Russian sturgeon (Acipenser gueldenstaedti) fry

A study of the effect of a complex probiotic preparation with bacteria of the genus Bacillus and a microdose of larvae of the fly Hermetia illucens on the physiological. parameters of fish has been carried out. It was established that introduction of the complex into artificial feeds for tilapia and Russian sturgeon juveniles during their incubation in recirculating aquaculture systems improves the digestion efficiency and increases the rate of fish growth and body mass accumulation. In tilapia, a decrease in the cholesterol level was revealed, while in sturgeon, an increase in the hemoglobin content was found. It was noted that a probiotic with biologically active agents H. illucens had a stimulating effect on the development of sexual gonads in female sturgeon fry, promoted an increase in the ovary mass, and provided for the development of eggs without morphological disturbances.

Growth response, body composition, plasma metabolites, digestive and antioxidant enzymes activities of Siberian sturgeon (Acipenser baerii, Brandt, 1869) fed different dietary protein and carbohydrate: lipid ratio

Knowing the effect of dietary nutrients on physiological parameters, especially oxidative stress, during fish rearing can be useful to improve fish health and optimize production in aquaculture. In this study, four iso-energetic (2 × 2 factorial design) diets differing in nutrient composition were submitted to the Siberian sturgeon juveniles, to analyse biochemical and physiological responses. The juveniles were fed for as long as 10 weeks with the following diets: low protein–high carbohydrate (CHO): lipid ratio (LP-St), high protein–high CHO: Lipid ratio (HP-St), low protein-low CHO: Lipid ratio (LP-L) and high protein-low CHO: Lipid ratio (HP-L). It was shown that HP-L diet significantly induced higher growth performance in the juveniles than LP-L; however, there was not a significant difference between them with other treatments. HSI was increased by higher dietary CHO: L ratio. The result obviously showed the higher dietary fat led to an increase in sturgeon body fat content. In addition, dietary protein and CHO: lipid ratio significantly affected plasma metabolites (glucose, cortisol, cholesterol and triglyceride) but did not affect IGF-1 and insulin levels. Based on enzyme activities results, incorporation of high protein (44%) in the diet induced lower amylase activity and carbohydrate digestion in the sturgeon juveniles. Moreover, antioxidant enzyme activities in this species were more influenced by lipid than other nutrients. In conclusion, using appropriate carbohydrates (~30%) in the sturgeon diet helps to spare protein. Furthermore, it is suggested to decrease the amount of lipid in high protein diet, to improve higher sturgeon fillet quality and less oxidative damage in liver.

The combined effects of feeding time and dietary lipid levels on growth performance in juvenile beluga sturgeon Huso huso

Juvenile beluga sturgeon, Huso huso (initial weight 50 ± 0.2 g), were fed with two lipid levels (120 g kg−1 lipid as low-energy diet, LE; 240 g kg−1 lipid as high-energy diet, HE) at different feeding times for 8 weeks, and the effects on growth, hematology, muscle composition, and apparent digestibility coefficients of dry matter, lipid, and protein were examined. Feeding times were as follows: (1) at 09:00 and 16:00 (under light regime), (2) at 21:00 and 04:00 (under dark regime), and (3) at 13:00 and 20:00 (under light–dark regime). Dietary lipid levels did not affect the hematological indices or apparent digestibility coefficients of dietary nutrients (P > 0.05); however, they affected the growth and muscle composition (P 0.05). Accordingly, juvenile beluga sturgeon can be fed at different times of the day without suffering growth loss, because probably, they have a low dependency on vision to detect food.

Effects of dietary lipid sources on growth performance, lipid metabolism and antioxidant status of juvenile Russian sturgeonAcipenser gueldenstaedtii

Six isonitrogenous and isoenergetic diets were used to test the influence of lipid source on growth performance, antioxidant status and lipid metabolism of juvenile Russian sturgeon, Acipenser gueldenstaedtii. Each diet was supplemented with 90 g kg−1 of lipid from each of six sources including fish oil (FO), beef tallow (BT), sunflower oil (SO), linseed oil (LO) and equal combinations of FO + SO + BT (FSB) or LO + SO + BT (LSB). After 56 days, fish fed LSB demonstrated highest weight gain, specific growth rate and lowest hepatosomatic index among all groups. The n-6 polyunsaturated fatty acids (PUFAs) in the whole fish were highest in the SO group, and n-3 PUFAs were highest in fish fed LO. The fish fed FO contained highest n-3 highly unsaturated fatty acids. Triglyceride in the serum of fish fed LSB was lowest, but was not significantly different from that in the SO group. Triglyceride in the serum of fish fed FO and BT was highest among all groups. Lipase, malate dehydrogenase and lipoprotein lipase activities were highest in fish fed LSB. Serum malondialdehyde in fish fed LSB was significantly lower than in fish fed FO or SO, but no significant differences were found among fish fed LSB, BT, LO or FSB. Fish fed LSB showed higher catalase activity and total antioxidant capacity than fish fed FO or FSB. This study indicates that linseed, sunflower oil and BT mixed oil are a suitable lipid source and can benefit growth performance and antioxidation in juvenile sturgeon.

Oxygen consumption and swimming behavior of juvenile Siberian sturgeon Acipenser baerii during stepped velocity tests

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 24:211-217 (2016) - DOI: https://doi.org/10.3354/ab00649 Oxygen consumption and swimming behavior of juvenile Siberian sturgeon Acipenser baerii during stepped velocity tests Xi Yuan1,2,3, Lu Cai3,4, David M. Johnson3,5, Zhiying Tu3, Yingping Huang3,* 1Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China 2University of Chinese Academy of Sciences, Beijing 100039, China 3Engineering Research Center of Eco-environment in Three Gorges Reservoir Region, Ministry of Education, China Three Gorges University, Hubei Yichang 443002, China 4Key Laboratory of Ecological Impacts of Hydraulic-Projects and Restoration of Aquatic Ecosystem of Ministry of Water Resources, Institute of Hydroecology, Ministry of Water Resources and Chinese Academy of Sciences, Wuhan 430079, China 5School of Natural Sciences and Mathematics, Ferrum College, Ferrum, VA 24088, USA *Corresponding author: chem_ctgu@126.com ABSTRACT: Oxygen consumption rate (MO2) and critical swimming speed (Ucrit) of juvenile Siberian sturgeon Acipenser baerii were measured at 24°C using a step-wise velocity test in a flume-type respirometer. Swimming behavior was video-recorded before and after the swimming experiment in a respirometer and an open tank. The relationship between MO2 and swimming speed (U) can be accurately described by a power function. The Ucrit of A. baerii was found to be 2.28 ± 0.09 body lengths (BL) s-1 or 0.51 ± 0.05 m s-1. The standard metabolic rate was calculated to be 149.24 mg O2 kg-1 h-1, and measured maximum metabolic rate (MMR) was 385.04 mg O2 kg-1 h-1. This is a relatively low MMR, resulting in a low metabolic scope, and is consistent with the low Ucrit of juvenile sturgeon. Excess post-exercise oxygen consumption, measured over a 60 min recovery period, was 65.20 mg O2 kg-1. Therefore, A. baerii possess high fatigue recovery capability. Tail beat frequencies increased significantly with U, but there was very little change in tail beat amplitude, and results differed between respirometer and open tank observations. Our results provide data on the physiology and behavior of A. baerii and will help to support conservation of this important species. KEY WORDS: Siberian sturgeon · Swimming capability · Swimming behavior · Oxygen consumption Full text in pdf format PreviousNextCite this article as: Yuan X, Cai L, Johnson DM, Tu Z, Huang Y (2016) Oxygen consumption and swimming behavior of juvenile Siberian sturgeon Acipenser baerii during stepped velocity tests. Aquat Biol 24:211-217. https://doi.org/10.3354/ab00649 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 24, No. 3. Online publication date: March 17, 2016 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2016 Inter-Research.

Chemical and electrical approaches to anesthesia of Ship sturgeon, Acipenser nudiventris: induction and recovery, physiological response to anesthesia

In this study, we investigated the induction and recovery times and physiological response of juvenile Ship sturgeon, Acipenser nudiventris anesthetized by CO2 (bar), clove powder (mg/L), and available electric shock (V). The shortest and longest induction time was for electric shock and clove powder, respectively. By contrast, the shortest and longest recovery time took place for electric shock and clove powder, respectively. Cortisol and glucose levels increased in 1 and 6 h after anesthesia. Changes in plasma osmolality and hematological indices were less changed among the anesthesia treatments. Results demonstrated that electric shock was a more effective method for quick induction time and prevented stress response caused by anesthesia, although all anesthetic methods were considered to be safe.

Stable isotope characterization of Rainy River, Ontario, lake sturgeon diet and trophic position

Abstract Lake sturgeon ( Acipenser fulvescens ) are considered threatened and many populations have declined since the early 1890s. Limited food web studies have been conducted with lacustrine lake sturgeon populations while similar studies do not exist for riverine populations. We use stable isotope analysis to study the diet composition of lake sturgeon captured in the Rainy River, Ontario. Historical reports of lake sturgeon consumption of fish and fish eggs exist, but both prey have largely been considered as a minor contribution to the overall diet of lake sturgeon. More recent dietary studies have focused on juvenile sturgeon and report low or no incidence of fish or fish eggs in lake sturgeon diets. The results of the stable isotope studies of Rainy River lake sturgeon suggest they obtain a large portion of their energy from organic material derived directly or indirectly from fish. Results parallel those recently reported for adult sturgeon in Lake Winnebago, Wisconsin, and are important in the context of contributing modern technical verification to earlier historical reports of fish and fish eggs in lake sturgeon diets. The results of this study provide evidence of potential seasonal or temporal shifts in lake sturgeon diet and further evidence to the potential shift in resource use based on life stage. Estimates of isotopic niches for the Rainy River sturgeon establish an important baseline for future changes in food web structure that might accompany the introduction of invasive species or the addition of anthropogenic stressors that could have implications for lake sturgeon conservation.

Laboratory test of suspended sediment effects on short-term survival and swimming performance of juvenile Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus, Mitchill, 1815)

Tested was the hypothesis that juvenile Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) would exhibit no response in short-term survival or swimming performance when exposed to varying concentrations of suspended sediment simulating dredge plumes in waterways where this species may be impacted by dredging operations. Sediment collected from Savannah Harbor, South Carolina, USA was used to simulate a worst-case scenario. Juvenile sturgeon were contained for a 3-day period in flow-through aquaria, with limited opportunity for movement, in sediment of varying concentrations (100, 250 and 500 mg L−1 total suspended solids [TSS]) mimicking prolonged exposure to suspended sediment plumes near an operating dredge. Of the 90 fish exposed, 86 (96%) survived the test. Of the four fish that died, one was exposed to 250 TSS and three to 500 TSS. Swimming performance results indicated that nearly all fish were positively rheotactic. Critical swim speeds (Ucrits) were moderate, whether measured as absolute values (21–31 cm s−1) or as relative values (1.4–2.1 body lengths s−1), with no significant differences among treatments (F < 0.83, P ≥ 0.4874). Behavior was dominated by contact-based locomotion and station-holding. Absence of substantial or significant immediate effects on survival and swimming performance suggest that impacts of sediment plumes in nature, where fish have freedom of movement and the power to escape rapidly, are minimal.