Using adaptive resolution imaging sonar to investigate Chinese sturgeon (Acipenser sinensis Gray, 1835) behaviour on its only spawning ground in the Yangtze River

The present study investigated the presence of Chinese sturgeon Acipenser sinensis on its only remaining spawning ground (below the Gezhauba Dam), and monitored the behaviour under different environmental conditions from 24 December 2015 to 23 January 2016. A fixed ARIS (Adaptive Resolution Imaging Sonar) system was used and a total of 72 Chinese sturgeon were detected during nine observations. Detections initially recorded a few A. sinensis in the early days of late‐December 2015, with an increase in recordings, leading to a peak in early‐January 2016 and declining thereafter. Water temperature slowly decreased during the study period from 18.1 to 15.7°C. During the middle of this temperature decline the sturgeon observations peaked, suggesting that Chinese sturgeon could have an optimal temperature range. The sturgeon Detections Per Unit Effort (DPUE) was higher in the night hours, peaking before dawn, suggesting a circadian behaviour rhythm. Sturgeon spawning was not observed during the investigation period. A delay in the decrease in water temperature caused by the Three Gorges Reservoir and the few numbers of reproductively mature individuals are suspected to have contributed to the failure in natural breeding.     

长江口中华鲟幼鱼对底质的选择

采用单因子实验方法,研究了中华鲟幼鱼对沙(直径＜0.2 cm)、小砾石(直径1～2 cm)、中砾石(直径4～5 cm)、大砾石(直径13～15 cm)4种底质类型的选择.结果表明:单尾鱼实验时,中华鲟幼鱼(体长283.0 mm±18.6 mm,体质量86.2 g±17.8 g,n=30)在4种底质中的时间百分比分别为沙51.50%±21.20%、小砾石20.27%±9.70%、中砾石18.03%±6.17%、大砾石10.20%±11.20%,幼鱼在沙底质中时间明显长于其它3种底质,且差异极显著(P＜0.01);多尾鱼实验时,中华鲟幼鱼(体长278.0 mm±14.3 mm,体质量79.2 g±19.6 g,n=30)在4种底质中的数量百分比分别为沙46.25%±8.06%、小砾石19.38%±7.72%、中砾石18.75%±7.19%、大砾石15.63%±8.92%,幼鱼在沙质底质中的数量明显高于其它3种底质,且差异极显著(P＜0.01);多尾鱼实验中,活动鱼(在水层中游动,不贴底)在4种底质中的数量无显著差异(P＞0.05);非活动鱼(贴底游动或静止)在沙底质中的数量显著高于其它3种底质(P＜0.01).单尾鱼(从时间角度)和多尾鱼(从数量角度)实验均表明,中华鲟幼鱼明显选择沙底质.     

Assessing the effect of the Three Gorges reservoir impoundment on spawning habitat suitability of Chinese sturgeon (Acipenser sinensis) in Yangtze River,China

The Chinese sturgeon (Acipenser sinensis), a kind of maricolous anadromous migratory fish species, is endangered and protected in China. Historical spawning habitats were distributed in the lower reaches of Jinsha River and the upper reaches of Yangtze River. Since the establishment of the Gezhouba water conservancy pivot in 1981, the migratory route of Chinese sturgeon spawning was blocked. Therefore, the fish was forced to propagate in a new spawning ground which was mainly distributed in the 4-km-long mainstream from Gezhouba Dam to Miaozui in the middle Yangtze River. After water storage and power generation of the Three Gorges reservoir (TGR) in 2003, the propagation of Chinese sturgeon has been impacted gradually. According to field surveys, the fish used to spawn twice a year before TGR impoundment, but only once happened after that. Besides, the spawning scale is also declining with each passing year.In order to simulate and evaluate the effect of TGR impoundment on spawning habitats of Chinese sturgeon, with consideration of their reproductive characteristics, an eco-hydrodynamic model was established by coupling a two-dimensional hydrodynamic model and a fuzzy fish habitat module based on fuzzy logic inference. Flow fields at the studied site in an impoundment scenario and an assumed no impoundment scenario were simulated with the 2D hydrodynamic model. Afterwards, by linking hydrodynamic conditions to the expert knowledge base, the fuzzy habitat model used fuzzy logic inference to compute habitat suitability of the Chinese sturgeon. In addition, the approach was used to propose a suitable instream flow range during the propagation period for Chinese sturgeon. The results indicated that the suitable instream flow needed for Chinese sturgeon spawning in middle Yangtze River should be between 10,000 m³/s and 17,000 m³/s and it also showed that after TGR was put into pilot impoundment operation at the designed water level of 175 m, the habitat suitability has decreased significantly in October. Besides, the water temperature of spawning habitat increased to a higher level in propagation period due to the impoundment of the TGR. All these alterations have had imposed tremendous impacts on the propagation of Chinese sturgeon. Therefore, adjusting impoundment schedule of the TGR to recover the water flow over spawning habitat in October is a crucial way to improve the habitat suitability. Furthermore, the presented method also provides a theoretical basis for further research on the assessment of habitat suitability of aquatic species at a micro-habitat scale.     

Migrations and movements of adult Chinese sturgeon Acipenser sinensis in the Yangtze River, China

From 2006 to 2009, 27 ultrasonic-tagged wild adult Chinese sturgeon Acipenser sinensis [eight males, 19 females; total length (L(T)) range = 245-368 cm] were captured on the spawning ground just downstream of Gezhouba Dam (GZD) in the Yangtze River. Twenty-six individuals were tracked for 7 to 707 days (mean number of relocations = 859; range = 3-4549). Acipenser sinensis movements were divided into four categories: (1) spawning migration, two tagged A. sinensis (one female and one male) returned to the Yangtze River and migrated from the Yangtze Estuary (river kilometer, rkm, 0) to the spawning ground (1678 rkm) between June and October. Their mean upstream ground speed was 1.41 km h(-1) (range = 0.26-2.35 km h(-1) ). The speed of the male was faster than the female; (2) pre-spawning holding, four of five females tagged in November 2008 stayed within 1678.00-1674.15 rkm for c. 1 year before the spawning period; (3) spawning movements, all A. sinensis swam mostly from the tailrace of the GZD (1678 rkm) to the Miaozui (1674.15 rkm) reach and some moved downstream c. 18.21 rkm (range = 3.93-24.64 rkm), but then, returned upstream to the GZD. Most tagged A. sinensis were on the spawning ground on the day when the spawning occurred; (4) post-spawning migration males (n = 6) and females (n = 2) departed the spawning area on a different time schedule, females leaving before males. The mean seaward ground speed of six A. sinensis was 4.87 km h(-1) (range = 0.68-7.60 km h(-1) ). There were no significant differences (P > 0.05) in ground speeds among reaches or between sexes within reaches between telemetry receivers. These broad spatiotemporal scale results will help establish an effective protection strategy for the species in the Yangtze River.     

Potential causes of habitat degradation and spawning time delay of the Chinese sturgeon (Acipenser sinensis)

In fish conservation, it is important to simulate fish habitat suitability and determine the potential impact on habitat quality and species behavior. This study analyzed the impact of several hydraulic projects on fish habitat quality and spawning time by numerical modeling. The case study involved the only Chinese sturgeon spawning site in the Yangtze River, China. Four habitat assessment indexes reflected both habitat quality and spatial characteristics, including fragmentation and connectivity. Previous studies did not simulate the water temperature impact on the fish habitat; spawning time delay was attributed to water temperature increases and discharge decreases. The results of the present study showed that the water temperature increase from the Three Gorges Reservoir (TGR) impoundment primarily caused the habitat degradation and spawning time delay. The effect of the water temperature increase on the degradation of average habitat suitability was eight times that of a decrease in discharge. A 25-day delay in the water temperature trend line was significantly correlated with a 26-day delay in the first spawning date. A decrease in discharge after TGR impoundment did not cause the spawning date delay. The Dike Project mainly impacted spawning site connectivity. Controlling the water temperature of the released water discharge is the most important means of conserving the wild Chinese sturgeon. This research can benefit other regions considering hydraulic projects by identifying potential factors impacting fish habitat quality and overall ecosystem health.     

Behavioural modifications in the early life stages of Siberian sturgeon (Acipenser baerii, Brandt)

Behavioural modifications of Acipenser baeri were studied during early ontogeny at 18 °C by means of specific tests and general observations. During A. baeri ontogeny, several different periods could be clearly distinguished by behavioural patterns. From hatching to 3 days post hatch (p.h.), specimens exhibited swimming-up and drift behaviour. A transition from a pelagic to benthic behaviour occurred between 4–5 days p.h. and specimens were positively rheotactic. At 7–8 days p.h., prelarvae aggregated into schools of different shapes. During prelarval development, specimens were positively phototactic, preferred white bottoms and did not show any preference for bottom concealment. Between 9–10 days p.h. coinciding with the onset of the exogenous feeding, larvae were active bottom swimmers, schooling behaviour disappeared and larvae dispersed. During early ontogeny, changes in body coloration were observed among those specimens who swam over bottoms of different brightness and during the day/night cycle. From 9 to 12 days p.h., larvae were positively phototactic, denied bottom cover and showed preference for white substrates. At 13 days p.h., the percentage of fish exhibiting positive phototactism, preferring open to concealed bottom habitats and white bottoms started to decrease, while at 20 days p.h. specimens showed a clear preference for bottom concealment and black and greyish bottoms. The significance, use and evolution of the former behavioural patterns is deeply discussed.     

中华鲟视网膜早期发育及趋光行为观察

视觉在鱼类摄食、集群、繁殖及洄游等活动中起着重要的信息传递作用,深入研究鱼类的视觉特性,对阐明其行为机制,了解视觉结构在不同发育时期的生态适应性具有重要意义[1]。鱼类和其他脊椎动物一样,感光细胞由感受强光的视锥细胞和感受弱光的视杆细胞组成。鱼类受到不同光强度照射时,能以不同的方式调节达到光感受细胞的有效光强度,从而适应于光亮或者黑暗的环境。鱼类感知光线刺激后能产生定向性运动,称为趋光反应。渔业生产上的光诱捕鱼根据这种特性用集鱼灯将鱼诱集到预定的水域进行捕捞,可大大提高渔获量。中华鲟(Acipenser sinensisGra…     

The skull of the Chinese sturgeon,Acipenser sinensis (Acipenseridae)

The Chinese sturgeon, Acipenser sinensis, is a large member of Acipenseridae now found only in the Yangtze River and the Yellow and East China seas. The goal of this paper was to describe the skull of A. sinensis in the context of recent anatomical and systematic studies of sturgeons. Five specimens (354–670 mm standard length) were prepared as skeletons. The left and right parietals and frontals are broadly separated by a median fontanelle. The lateral‐most lateral extrascapular variably supports the confluence of the supratemporal, occipital and trunk lateral lines. There is no distinct ventral supraorbital process as found in other sturgeons. The anterodorsal portion of the snout is unique among Acipenseridae by having a single large anamestic dorsal rostral bone instead of a series of separate dorsal rostral bones. There are 0–2 lateral rostral bones on each side positioned anterior to but not in contact with the horizontal arm of the jugal. The dorsal surface of the neurocranium lacks a pineal opening, and its anterior tip is sharply pointed in the smaller specimens examined and gently curved in larger specimens. The anteromedial arm of the palatopterygoid is broad relative to other acipenserids. These new morphological data are discussed and compared among Acipenseridae.     

Microsatellites assessment of Chinese sturgeon (Acipenser sinensis Gray) genetic variability

Four microsatellites were used to examine the genetic variability of the spawning stocks of Chinese sturgeon, Acipenser sinensis, from the Yangtze River sampled over a 3‐year period (1999–2001). Within 60 individuals, a total of 28 alleles were detected over four polymorphic microsatellite loci. The number of alleles per locus ranged from 4 to 15, with an average allele number of 7. The number of genotypes per locus ranged from 6 to 41. The genetic diversity of four microsatellite loci varied from 0.34 to 0.67, with an average value of 0.54. For the four microsatellite loci, the deviation from the Hardy–Weinberg equilibrium was mainly due to null alleles. The mean number of alleles per locus and the mean heterozygosity were lower than the average values known for anadromous fishes. Fish were clustered according to their microsatellite characteristics using an unsupervised ‘Artificial Neural Networks’ method entitled ‘Self‐organizing Map’. The results revealed no significant genetic differentiation considering genetic distance among samples collected during different years. Lack of heterogeneity among different annual groups of spawning stocks was explained by the complex age structure (from 8 to 27 years for males and 12 to 35 years for females) of Chinese sturgeon, leading to formulate an hypothesis about the maintenance of genetic diversity and stability in long‐lived animals.     

Growth and feeding ecology of juvenile Chinese sturgeon,Acipenser sinensis,in the Yangtze Estuary

The present study was conducted to assess growth and the feeding ecology with prey preferences of juvenile Acipenser sinensis individuals in the Yangtze Estuary from May to August, 2015. From May to August, juveniles grew from 11.65 ± 2.10 cm (10.82 ± 6.32 g) to 27.78 ± 3.36 cm (158.08 ± 60.50 g), and the length‐weight relationship (b = 3.1124) indicated isometric growth. The stomach content analysis indicated the following order of dominance of prey groups: fish, crab, amphipoda, polychaeta, shrimp and other small benthic invertebrates. The main diet taxon has not changed dramatically compared with samples in 2004. Moreover, this study confirmed that changes occurred in the prey composition, which was different with the growth of length size in the Yangtze Estuary. Therefore maintaining species richness in the Yangtze Estuary and ensuring sufficient food source is crucial to species conservation of A. sinensis.     

Biology and life history of Dabry's sturgeon, Acipenser dabryanus, in the Yangtze River

Dabry's sturgeon, Acipenser dabryanus, is a relatively small (130 cm, 16 kg) and now rare sturgeon restricted to the Yangtze River Basin. It behaves as a resident freshwater fish, does not undertake long distance migrations (except for spawning), and lives in a variety of habitats. It historically spawned in the upper Yangtze River, but the spawning sites are unknown. Acipenser dabryanus reaches maturity earlier than do other Chinese sturgeons, which gives the species aquaculture potential, and artificial spawning has been carried out. However, the native population in the Yangtze has sharply declined in the last two decades due to overfishing, pollution and habitat alteration and destruction, especially since the construction of the Gezhouba Dam, which was built in 1981 across the Yangtze River at Yichang, Hubei Province. Since 1981, Dabry's sturgeon rarely occurs below the Gezhouba Dam because downstream movements are blocked. Clearly, conservation of Dabry's sturgeon must be emphasized. Conservation methods may include protecting habitats, controlling capture and stock replenishment.     

Molecular cloning and functional analysis of Chinese sturgeon (Acipenser sinensis) growth hormone receptor

A full length cDNA encoding the growth hormone receptor (GHR) of Chinese sturgeon was cloned in order to investigate the mechanism of growth hormone in regulating the growth of Chinese sturgeon. The open reading frame of the cloned Chinese sturgeon growth hormone receptor (csGHR) cDNA encodes a trans-membrane protein of 611 amino acids containing all the characteristic motifs of GHR. By sequence alignment, substitutions of amino acid residues highly conserved in other species were identified. Using the CHO cell culture system, the function of csGHR and the biological significance of the amino acid substitution in csGHR were examined. The promoter of serine protease inhibitor 2.1 (Spi2.1) was trans-activated upon stimulation of seabream GH (sbGH) in the csGHR-expressing CHO cells. Furthermore, CHO cells stably expressing csGHR were stimulated to proliferate by sbGH. In agreement with our previous report, Chinese sturgeon growth hormone-binding protein (csGHBP) was detected in the culture medium of CHO cells stably expressing csGHR. Mutation of Asp residue in the ligand binding motif in csGHR to Glu significantly enhanced csGHR’s biological function, whereas mutation of Asp residue to Ala decreased its biological function. The results demonstrated that the cloned csGHR was of full biological function and the csGHBP could be generated through proteolysis of csGHR. These findings might provide new insights into thoroughly understanding the regulatory mechanism of Chinese sturgeon growth.     

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.