The Holocene occurrence of Acipenser spp. in the southern North Sea: the archaeological record

Archaeological sturgeon remains from the southern North Sea basin used to be automatically attributed to Acipenser sturio, since this was the only acipenserid species believed to occur there. These species identifications, however, were in need of revision after a growing number of indications were found for the historical presence of Acipenser oxyrinchus in western Europe. In this study, morphological and genetic data on sturgeon remains from archaeological sites along the southern North Sea are revised. A large number of Dutch, Belgian, British and some French archaeological sturgeon remains, dating from the Mesolithic up to Late Modern times, are morphologically examined and fish sizes are reconstructed. This study of >7000 acipenserid bones proves the sympatric occurrence of European sturgeon A. sturio and Atlantic sturgeon A. oxyrinchus in the southern North Sea at least since the Neolithic (fourth millennium BC onwards), with A. oxyrinchus remains always outnumbering those of A. sturio. Human influence is documented by the decrease in finds through time, but no clear evidence was found for a diachronic change in fish lengths that could possibly be related to fishing pressure.     

Comparison of karyotypes of <Emphasis Type="Italic">Acipenser oxyrinchus</Emphasis> and <Emphasis Type="Italic">A. sturio</Emphasis> by chromosome banding and fluorescent in situ hybridization

A highly debated problem in Acipenseridae taxonomy is whether Acipenser oxyrinchus (North American Atlantic sturgeon) and A. sturio (European Atlantic sturgeon) are true species: a detailed comparison of their karyotypes could provide relevant information. Here we describe for the first time the karyotype of A. oxyrinchus (2n = 121 ± 3), and its features, among which the constitutive heterochromatin, revealed by C-banding technique, the distribution of telomeric regions, and the 5S rRNA genes, detected by FISH. The results reveal that A. oxyrinchus and A. sturio karyotypes and features are quite similar. Moreover, comparing the results obtained through hybridization by FISH with HindIII and PstI satellite DNA in these and in other sturgeon species, no hybridization signals are detected in A. sturio and A. oxyrinchus, while A. stellatus and A. gueldenstaedtii show hybridization. Thus A. sturio and A. oxyrinchus appear very similar from a cytogenetic point of view: these and molecular data repeatedly point out that A. sturio and A. oxyrinchus represent a sister clade in comparison to all other sturgeon species up to now studied.     

Genetic Identification of Western Mediterranean Sturgeons and its Implication for Conservation

To date, the only native sturgeon species in Western Europe was believed to be Acipenser sturio. However, this species is currently restricted to the Gironde River (Southern France), and it poses serious difficulties for rearing in captivity and for using in recovery programme. Furthermore, it has been questioned whether A. sturio is in fact the only species within the rivers of Western Europe, as A. naccarii, a species previously considered endemic of the Adriatic region, has been reported from the Iberian Peninsula in recent years. Here, we have used forensic techniques to obtain DNA from several museum specimens of sturgeons caught in the Spanish Guadalquivir River and in other European rivers. We analysed DNA sequences from these specimens for five genetic markers (three nuclear and two mitochondrial regions), which were subsequently compared with sequences obtained from A. sturioand A. naccarii. Our study demonstrates that A. naccarii coexists withA. sturio, from the Adriatic Sea to the Iberian Peninsula, a finding that could be taken into account in future sturgeon recovery programmes in Western Europe.     

Inter‐ and intraspecific variation in the surface pattern of the dermal bones of two sturgeon species

Archaeological bone remains of sturgeon (Acipenser sturio/Acipenser oxyrinchus) from northwestern Europe are often identified to species on the basis of their surface morphology and then used to reconstruct the spatial distribution of the two species through time. The dermal bones of A. sturio are said to have an exterior surface pattern consisting of tubercles, while those of A. oxyrinchus are said to display alveoli. In the present paper, the validity of the surface pattern as a species‐specific characteristic is critically assessed. To this purpose, dermal plates from modern, genetically identified museum specimens were studied and the surface morphology observed in a series of archaeological remains was compared with the genetic identifications obtained on these same remains. The analyses show that the surface pattern of dermal bones is related to the size of the individual, with the pattern of small A. oxyrinchus being similar to that of A. sturio. In addition, variations in the surface pattern among the bones of a single individual and within the same bone have been observed. These findings explain previous conflicting results between morphological and genetic identifications and allow the formulation of some recommendations for more accurate morphological identification of isolated archaeological sturgeon dermal bones.     

Assessing the potential of the European Atlantic sturgeon Acipenser sturio to control bivalve invasions in Europe

This pilot study explored the potential of juvenile European Atlantic sturgeon Acipenser sturio to feed on two invasive bivalve species, the Asian clam Corbicula fluminea and the Eurasian zebra mussel Dreissena polymorpha. Preliminary results indicate that native A. sturio were feeding on D. polymorpha at a very limited rate and their potential to prevent the establishment of invasive bivalve species, in new and previously invaded areas, is considered limited.     

Sturgeons in Greece: a review

In the past, sturgeons were practically unknown in Greece, both to the public and to scientists, the latter not having had the opportunity to study wild populations of the four native species. Populations of stellate sturgeon (Αcipenser stellatus Pallas, 1771), Adriatic sturgeon (Acipenser naccarii Bonaparte, 1836), and beluga sturgeon (Huso huso L., 1758) gradually collapsed by the end of the 1970s. Only the River Evros (Thrace, N.W. Greece) sustained a small fishery and caviar canning operation with European sturgeon (A. sturio L., 1758) until 1975. Collapse of stocks was mainly attributed to overfishing, pollution and damming. Sturgeons became widely known after initial farming efforts by the Municipal Hatchery at Lake Ioannina in 1992. Broodstock or fertilized eggs of species with high aquaculture potential, such as sterlet (Acipenser ruthenus L., 1758), Russian sturgeon (Acipenser gueldenstaedtii Brandt, 1833), bester hybrid (A. ruthenus ×H. huso), paddlefish (Polyodon spathula Walbaum, 1792), Siberian sturgeon (Acipenser baerii Brandt, 1869) and white sturgeon (Acipenser transmontanus Richardson, 1836) were imported into Greece between 1992 and 2004. Hatchery technology, larval rearing and production systems are reviewed in this paper and, despite problems, past and present efforts appear to meet a particular interest of the aquaculture sector as well as of those interested in the restoration of wild stocks.     

From microsatellites to single nucleotide polymorphisms for the genetic monitoring of a critically endangered sturgeon

The use of genetic information is crucial in conservation programs for the establishment of breeding plans and for the evaluation of restocking success. Short tandem repeats (STRs) have been the most widely used molecular markers in such programs, but next‐generation sequencing approaches have prompted the transition to genome‐wide markers such as single nucleotide polymorphisms (SNPs). Until now, most sturgeon species have been monitored using STRs. The low diversity found in the critically endangered European sturgeon (Acipenser sturio), however, makes its future genetic monitoring challenging, and the current resolution needs to be increased. Here, we describe the discovery of a highly informative set of 79 SNPs using double‐digest restriction‐associated DNA (ddRAD) sequencing and its validation by genotyping using the MassARRAY system. Comparing with STRs, the SNP panel proved to be highly efficient and reproducible, allowing for more accurate parentage and kinship assignments' on 192 juveniles of known pedigree and 40 wild‐born adults. We explore the effectiveness of both markers to estimated relatedness and inbreeding, using simulated and empirical datasets. Interestingly, we found significant correlations between STRs and SNPs at individual heterozygosity and inbreeding that give support to a reasonable representation of whole genome diversity for both markers. These results are useful for the conservation program of A. sturio in building a comprehensive studbook, which will optimize conservation strategies. This approach also proves suitable for other case studies in which highly discriminatory genetic markers are needed to assess parentage and kinship.     

Historical presence of the sturgeon Acipenser sturio in the Rhône basin determined by the analysis of ancient DNA cytochrome b sequences

Sturgeon disappeared from the Rhône River in the mid 70’s without certitude about which species it was and about the existence of a sympatry between European sturgeon, Acipenser sturio, and Adriatic sturgeon, A. naccarii, in this watershed. In order to reach a reliable specific determination of this extinct sturgeon population, archaeozoological remains of the Jardin d’Hiver in Arles city, on the Rhône river banks, were genetically analysed, following strict criteria of authentication for the ancient DNA work. The rich collection of Arles sturgeon bone remains stems from human activities between the 6th and the 2nd Century BC. Sequences of 86 bp of the cytochrome b gene were obtained on four bones, from different anatomical parts of the fish and from different archaeological layers. All gave A. sturio diagnostic sequences. This preliminary analysis is an essential first step in the project of sturgeon reintroduction in the Rhône River. Thus, further analyses on a larger sample are necessary to comfort this result and to solve the question of sympatry with A. naccarii.     

Outmigration pathways of stocked juvenile European sturgeon (Acipenser sturio L., 1758) in the Lower Rhine River,as revealed by telemetry

Working towards a future Rhine Sturgeon Action Plan the outmigration pathways of stocked juvenile European sturgeon (Acipenser sturio L., 1758) were studied in the River Rhine in 2012 and 2015 using the NEDAP Trail system. A total of 87 sturgeon of 3 to 5 years old (n = 43 in 2012, n = 44 in 2015) were implanted with transponders and released in May and June in the river Rhine at the Dutch‐German border, approximately 160 km from the sea. In total three sturgeons (3%) were found dead on river banks within seven days after the release. Based upon their wounds these sturgeons were likely hit by ship‐propellers. Tracking results were obtained from 57 (66%) of the sturgeons, of which 39 (45%) indicated movement into the Port of Rotterdam. Here the sturgeons remained for an average of two weeks, which suggests they spent time to acclimatize to higher salinities before entering the North Sea. Of the 45 (52%) sturgeons that were confirmed to have entered the North Sea, ten (22%) were recaptured (mainly by shrimpers and gill‐nets) close to the Dutch coastline; nine were alive and were released. From the results we obtained the preferred outmigration pathways, movement speeds and an indication of impacting factors (i.e. ship propellers and bycatch). Bycatches provided also localisations information in the coastal area. A next step to complete this work would be to assess habitat selection in freshwater and downstream migration of young of the year (YOY sturgeons) in the Lower Rhine.     

Assessment of Extinction Risk and Reasons for Decline in Sturgeon

Sturgeon populations in the Danube River have been affected by a combination of hydropower development, over-harvesting, habitat degradation from agricultural and industrial practices and from urbanization. The effects of these changes have been monitored on six sturgeon species inhabiting the Danube River. Two of them are resident species, while the other four migrate to the river for spawning. Atlantic sturgeon (Acipenser sturio) has completely disappeared from this region. Ship sturgeon (Acipenser nudiventris) is very rare in professional fishing catches. Beluga (Huso huso), Russian sturgeon (Acipenser gueldenstaedtii), stellate sturgeon (Acipenser stellatus) and sterlet (Acipenser ruthenus) are endangered with different levels of extinction risk. Here, we model the time dependence of the beluga and Russian sturgeon catch in the Serbian part of the Danube River. Predicted extinction of Russian sturgeon was estimated to fall around the middle of the century, and for beluga approximately at middle of the millennium. Suggestions for sturgeon conservation measures on a national level and coordination of all relevant institutions in Serbia are also presented.     

Microsatellite development for the endangered Yangtze sturgeon (Acipenser dabryanus Duméril, 1869) using 454 sequencing

The Yangtze sturgeon (Acipenser dabryanus) is an endemic species in China. Using 454 sequencing, eight polymorphic tri‐, tetra‐, penta‐, and hexanucleotide microsatellite loci were isolated in this study. The raw sequence data from a one‐eighth run of 454 sequencings were 38.0 Mbp containing 94 222 reads/sequences. Of 80 microsatellite loci, only eight loci were polymorphic in a population of 30 individuals. The number of alleles per locus ranged from 4 to 14 (mean 7.62), and the observed heterozygosities varied between 0.46 and 0.88 (mean 0.74). Cross amplification was tested in congeneric species Acipenser sturio and Acipenser sinensis. These new microsatellite markers will be useful for further studies on genetic variation, parentage analysis, and conservation management for this critically endangered species.     

Interspecific hybridization in natural sturgeon populations of the Eastern Black Sea: the consequence of drastic population decline?

The eastern part of the Black Sea and its tributaries are suitable habitats for several sturgeon species, among which Acipenser gueldenstaedtii, A. stellatus, A. nudiventris, A. persicus, A. sturio, and H. huso are well documented. However, different threats have led these species to a dramatic decline, all of them are currently listed as Critically Endangered, and some Locally Extinct, in that area. We tested 94 wild sturgeon samples from the Black Sea and Rioni River by analyzing the mitochondrial Control Region and nuclear markers for hybrid identification. The data analyses (1) assessed mitochondrial diversity among samples, (2) identified their species, as well as (3) indicated instances of hybridization. The data collected, besides confirming a sharp decrease of catches of Beluga and Stellate sturgeon in recent years, also revealed four juvenile hybrids between Russian and Stellate sturgeon, providing the first evidence of natural interspecific hybridization in the Rioni. The present communication raises concerns about the status of sturgeon species in this area and underlines the urgent need for conservation programs to restore self-sustaining populations.

     

Assessing water quality suitability for shortnose sturgeon in the Roanoke River,North Carolina,USA with an in situ bioassay approach

The aim of this study was to determine the suitability of water quality in the Roanoke River of North Carolina for supporting shortnose sturgeon Acipenser brevirostrum, an endangered species in the United States. Fathead minnows Pimephales promelas were also evaluated alongside the sturgeon as a comparative species to measure potential differences in fish survival, growth, contaminant accumulation, and histopathology in a 28‐day in situ toxicity test. Captively propagated juvenile shortnose sturgeon (total length 49 ± 8 mm, mean ± SD) and fathead minnows (total length 39 ± 3 mm, mean ± SD) were used in the test and their outcomes were compared to simultaneous measurements of water quality (temperature, dissolved oxygen, pH, conductivity, total ammonia nitrogen, hardness, alkalinity, turbidity) and contaminant chemistry (metals, polycyclic aromatic hydrocarbons, organochlorine pesticides, current use pesticides, polychlorinated biphenyls) in river water and sediment. In the in situ test, there were three non‐riverine control sites and eight riverine test sites with three replicate cages (25 × 15‐cm (OD) clear plexiglass with 200‐μm tear‐resistant Nitex^® screen over each end) of 20 shortnose sturgeon per cage at each site. There was a single cage of fathead minnows also deployed at each site alongside the sturgeon cages. Survival of caged shortnose sturgeon among the riverine sites averaged 9% (range 1.7–25%) on day 22 of the 28‐day study, whereas sturgeon survival at the non‐riverine control sites averaged 64% (range 33–98%). In contrast to sturgeon, only one riverine deployed fathead minnow died (average 99.4% survival) over the 28‐day test period and none of the control fathead minnows died. Although chemical analyses revealed the presence of retene (7‐isopropyl‐1‐methylphenanthrene), a pulp and paper mill derived compound with known dioxin‐like toxicity to early life stages of fish, in significant quantities in the water (251–603 ng L^?1) and sediment (up to 5000 ng g^?1 dry weight) at several river sites, no correlation was detected of adverse water quality conditions or measured contaminant concentrations to the poor survival of sturgeon among riverine test sites. Histopathology analysis determined that the mortality of the river deployed shortnose sturgeon was likely due to liver and kidney lesions from an unknown agent(s). Given the poor survival of shortnose sturgeon (9%) and high survival of fathead minnows (99.4%) at the riverine test sites, our study indicates that conditions in the Roanoke River are incongruous with the needs of juvenile shortnose sturgeon and that fathead minnows, commonly used standard toxicity test organisms, do not adequately predict the sensitivity of shortnose sturgeon. Therefore, additional research is needed to help identify specific limiting factors and management actions for the enhancement and recovery of this imperiled fish species.     

A life‐stage population model of the European sturgeon (Acipenser sturio L., 1758) in the Elbe River. Part II: assessment of the historic population decline

A post‐hoc analysis on the decline of the European sturgeon (Acipenser sturio) population in the Elbe River was performed for the end of the 19th century. A modeling approach was applied to determine the role of various factors potentially impacting the population. Using an age‐structured population model developed for European sturgeon, the estimates of fishing efficiency in the Elbe were verified. Catches reported from 1850 to 1920 were used as a basis to identify the population size, dynamics of the decline and the impacts contributing to the population decline. According to results of the model, the historic population size of the European sturgeon in the Elbe River exceeded 450 000 individuals. The population revealed a significant response in abundance of adults towards the fishery directed at spawning migrants, even at low fishery effort. Unsustainable fishery was the initial cause of the population decline, while increasing pollution and habitat degradation revealed significant impacts after 1860. The results represent a good example for the fisheries ‘hyperstability’ phenomenon. In the case of the Elbe fishery, an increasing fishery effort was masking the actual population decline while temporarily maintaining the overall yield. The results indicate that, for sturgeons and other species with similar life history patterns, the use of fishery data for the assessment of population dynamics and fishery sustainability has to be applied with due caution, as it might produce false images of the population size and dynamics.     

A laboratory examination of substrate, water depth, and light use at two water velocity levels by individual juvenile pallid (Scaphirhynchus albus) and shovelnose (Scaphirhynchus platorynchus) sturgeon

We investigated the influence of substrate type, water depth, light, and relative water velocity on microhabitat selection in juvenile pallid (Scaphirhynchus albus) and shovelnose (Scaphirhynchus platorynchus) sturgeon. Individual sturgeon were placed in an 18 927 L elliptical flume, and their location was recorded after a 2‐h period. Data were analyzed using exact chi‐square goodness of fit tests and exact tests of independence. Both sturgeon species used substrate, depth, and light in similar proportions. (all comparisons; P > 0.05). Specifically, pallid and shovelnose sturgeon did not use substrate in proportion to its availability (pallid: P = 0.0026; shovelnose: P = 0.0199). Each species used sand substrate more and gravel substrate less than expected based on availability. Additionally, neither species used woody structure. Both species used deep areas in greater proportion than availability while shallow areas were used less than expected based on availability (pallid; P < 0.0001; shovelnose; P = 0.0335). Pallid and shovelnose sturgeon used very dark areas in greater proportion than expected based on availability; however, very light areas were used in lower proportion than expected (P < 0.0001). Overall, neither species changed their use of habitat in relation to a change in water velocity (pallid, all comparisons P > 0.05; shovelnose, all comparisons P > 0.05). This study is the first investigation of juvenile pallid and shovelnose sturgeon habitat selection in a large‐scale artificial stream system. Field studies of microhabitat selection by juvenile pallid and shovelnose sturgeon should be carried out to substantiate the results of this study, and to identify critical habitat for recovery and management of sturgeon species. Due to the extensive range, longevity, and migratory behavior of these fishes, proper management likely requires river improvements that provide sturgeon with access to a broad range of habitat conditions over time, including system‐wide habitat diversity; natural variation in flow, velocity, temperature, and turbidity; high water quality; a broad prey base; free‐flowing river sections which provide suitable spawning and rearing sites, as well as protection from recreational and commercial harvesting.     

Comparison of the Effects of Gonadotropic Preparations of the Carp and Stellate Sturgeon Pituitaries onin vivoand in vitroOocyte Maturation in the Siberian Sturgeon Acipenser baeriBrandt

Injections of 2.5 mg/kg of stellate sturgeon (Acipenser stellatusPall.) pituitary extract and 5 mg/kg of carp (Cyprinus carpioL.) pituitary extract in Siberian sturgeon (Acipenser baeriBrandt) females did not reveal significant differences in the effects of these preparations. There were no differences in the percentage of females that responded by ovulation, duration of the period from injection to ovulation, rate of ovulation, or quality of mature eggs as estimated by the percentage of fertilization or percentage of normal embryos at the small yolk plug stage. Thus, an insufficient efficiency in the artificial reproduction of the Siberian sturgeon grown in captivity is not related to the use of the carp pituitary preparation as a stimulus. Estimation of the ratio of specific activities of the pituitary extracts and purified gonadotropins of the stellate sturgeon and carp by in vitrooocyte maturation has shown that it varies within wide limits as a function of the medium composition and physiological state of follicles. Hence, the ratio of activities of the gonadotropins of different species as determined by in vitromaturation of sturgeon oocytes may markedly differ from that upon injection of these preparations in breeders.     

Length–weight relationship and a relative condition factor equation for lake sturgeon (Acipenser fulvescens) from the St Clair River system (Michigan, USA)

Several USA state, federal, and Canadian agencies study lake sturgeon (Acipenser fulvescens) within the St Clair River and Lake St Clair, collectively referred to hereafter as the St Clair River (SCR) system. Previously, there has been no set standard for determining condition for SCR system lake sturgeon. Condition measures the variation from the expected weight for length as an indicator of fatness, general well‐being, gonad development, etc. The aim of this project was to determine the length–weight relationship of lake sturgeon caught from the SCR system, from which a relative condition factor (K_n) equation could be derived. Total length (TL, mm) and weight (W, kg) were measured for 1074 lake sturgeon (101 males and 16 females were identifiable) collected by setline and bottom trawl from the SCR system in May–September, 1997–2002. Analysis of covariance found no difference in the length–weight relationship between sampling gear or sex. Least‐squares regression of log₁₀W × log₁₀TL produced the overall equation logW = 3.365logTL ? 9.320. Using the exponential form of the slope and y‐intercept, relative condition factor for lake sturgeon from the SCR system can be calculated as K_n = W/[(4.786 × 10^?10)(TL^3.365)]. Equations for males and females were also developed. Overall, body condition was significantly correlated with both age and girth; no significant difference in K_n by sex was found. In general, the SCR lake sturgeon population was near the upper ends of growth and condition ranges listed in the literature, comparable with those populations that are at similar latitudes. Although condition factors should be interpreted with caution, proper use of a standard equation provides a non‐lethal measure of overall fish health that can be used by biologists and managers in ongoing efforts to restore lake sturgeon throughout the Great Lakes.     

Environmental cues for natural reproduction of the Chinese sturgeon,Acipenser sinensis Gray, 1835, in the Yangtze River,China

For effective conservation, it is important to explore the environmental cues initiating the spawning activities of a fish species. Based on monitoring data gathered between 1998 and 2011, the relationships between spawning activities of the Chinese sturgeon, Acipenser sinensis, and several environmental cues were analyzed using the rare events logistic regression ‘Relogit’ method, which indicated that water temperature, 1‐day ?‐discharge, and atmospheric pressure were among the key spawning cues for A. sinensis (P < 0.05). It is suggested that Chinese sturgeon might have an optimal environment window of 17–20°C water temperature, high day‐to‐day discharge increase, and low atmospheric pressure for spawning. In support of Chinese sturgeon reproduction, suggested modifications to the operational procedures for the Three Gorges Reservoir (TGR) to trigger spawning are: lowering the downstream water temperature to below 20°C before mid‐October and expanding the period with water temperatures of between 17 and 20°C; to create a day‐to‐day intermittent increase in the discharge to an optimal spawning water temperature; and to regulate flow at nights with a low atmospheric pressure.     

Short‐term survival and dispersal of hatchery‐reared juvenile pallid sturgeon stocked in the channelized Missouri River

In the summer and fall of 2014, Nebraska Game and Parks Commission crews monitored juvenile pallid sturgeon, Scaphirhynchus albus (Forbes & Richardson, 1905) (age‐1 and age‐4) implanted with telemetry tags that were stocked in a side channel of the Missouri River in Nebraska, USA to gain knowledge into post‐stocking survival and dispersal. For this study, specific questions were asked: (i) what is the short‐term survival of stocked pallid sturgeon, (ii) do pallid sturgeon stocked in summer exhibit decreased survival rates due to increased water temperatures or high river discharge, and (iii) how quickly do pallid sturgeon disperse from a stocking site? Detection histories for two rounds were used to estimate apparent survival (Ø) and detection (p) rates using maximum likelihood estimators based on the standard mark‐recapture Cormack‐Jolly‐Seber model structure within program MARK. Overall apparent survival was 98.6% and dispersal was rapid; therefore, moratoriums on stocking pallid sturgeon during summer months or during high flow events do not appear to be warranted.     

Effects of temperature on growth,hematology, and immune responses of subadult Chinese sturgeon (Acipenser sinensis Gray 1835) under different ammonia nitrogen conditions in recirculating aquaculture system

The growth, hematology, and immune responses of subadult Chinese sturgeon (Acipenser sinensis) (avg. wt. 25.11 ± 3.74 kg) were determined at three water temperature levels (12, 18, and 24°C) × three concentrations of total ammonia nitrogen (TAN) (0.05 ± 0.02, 1.03 ± 0.04, and 2.03 ± 0.05 mg/L) for 90 days in recirculating aquaculture system (RAS). At the end of the experiment, all fish were weighed and serum was collected for analysis using biochemical parameters. The temperature level had significant effects on the growth and hematology responses of subadult Chinese sturgeon under the RAS conditions. The specific growth rate (SGR) of subadult Chinese sturgeon was highest at 18°C compared to other temperatures; at this temperature, the total antioxidant capacity (T‐AOC), alanine aminotransferase (ALT) and lysozyme (LZM) activities were also the highest (p < 0.05). As the temperature rose, the oxygen consumption rate and ammonia excretion rates significantly increased (p < 0.05). In addition, there was no effect of TAN level on ammonia excretion rates of subadult Chinese sturgeon, while the oxygen consumption rate was greater in the high TAN group compared with the other groups (p < 0.05). The SGR of the fish was markedly reduced when the TAN level rose, and blood urea nitrogen (BUN), blood ammonia (BA), malondialdehyde (MDA) and cortisol in the serum were significantly elevated when the fish were in high TAN water for 90 days (p < 0.05), T‐AOC and LZM activities in the serum clearly decreased, indicating that the antioxidant system and nonspecific immune mechanism of subadult Chinese sturgeon appeared to be inhibited, which could raise the sensitivity of the Chinese sturgeon to various pathogens. The results of this study indicate that subadult Chinese sturgeon could achieve normal growth in the RAS, but that growth and hematology were significantly affected when the TAN concentration in the water was higher than 2 mg/L for an extended period.