How different rearing temperatures affect growth and stress status of Siberian sturgeon Acipenser baerii larvae

Environmental temperature is one of the critical factors affecting fish development. The aim of this study was to examine the impact of three different rearing temperatures (16, 19 and 22°C) throughout the endogenous feeding phase of the Siberian sturgeon Acipenser baerii. This was performed by assessing (a) larval survival and growth; (b) immunofluorescence localization and expression of genes involved in muscle development and growth – myog and Igf1; and (c) stress status through the expression of thermal stress genes – Hsp70, Hsp90α and Hsp90β – and whole body cortisol. Overall survival rate and larval weight did not differ significantly across temperatures. Larvae subjected to 22°C showed faster absorption of the yolk-sac than larvae subjected to 19 or 16°C. Both at schooling and at the end of the trial, larvae reared at 16°C showed significantly lower levels of cortisol than those reared at 19 or 22°C. IGF-1 immunopositivity was particularly evident in red muscle at schooling stage in all temperatures. The expression of all Hsps as well as the myog and Igf1 genes was statistically higher in larvae reared at 16°C but limited to the schooling stage. Cortisol levels were higher in larvae at 22°C, probably because of the higher metabolism demand rather than a stress response. The observed apparent incongruity between Hsps gene expression and cortisol levels could be due to the lack of a mature system. Further studies are necessary, especially regarding the exogenous feeding phase, in order to better understand if this species is actually sensitive to thermal stress.     

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.     

施氏鲟仔鱼发育圾异速生长模型

施氏鲟仔鱼的生长发育可分为两个时期:卵黄囊期(或称为自由胚期),即从刚出膜(0日龄,10.17±0.63 mm)到初次开口(9日龄,18.93±0.74 mm);晚期,从开口摄食至器官发育基本完全(38日龄,41.89±5.09 mm).卵黄囊期仔鱼的感觉、摄食、呼吸、游泳等器官快速分化;晚期仔鱼各骨板分化并发育,在形态上逐渐完成向成鱼的转变.对施氏鲟仔鱼异速生长进行的研究表明,仔鱼许多关键器官均存在异速生长现象,如眼径、口宽、尾鳍长、胸鳍长分别在2日龄、8~9日龄、10日龄、11日龄出现生长拐点,拐点之前器官快速生长,拐点之后生长速度减慢甚至近似等速生长.施氏鲟仔鱼各器官呈现出协调和快速发育的特征,随着重要的感觉、摄食、呼吸、游泳等器官的发育和完善,仔鱼快速地具备了躲避敌害和摄食的能力,其生存能力大大提高.     

Hydrological Status of the spawning ground of Acipenser sinensis underneath the Gezhouba Dam and its relationship with the spawning runs

The spawning runs of Chinese Sturgeon (CS; Acipenser sinensis) were observed 37 times below Gezhouba Dam of Yangtze River between 1983 and 2004. Five hydrological factors (water temperature, water level, flow discharge, silt content and current velocity) were monitored on a daily basis at the spawning ground between October and November for 22 consecutive years (1983–2004). The effect of current velocity on the spawning ground at the bottom layer of the river, where CS was spawning for four years, was measured (1996–1999). The authors of this study analyzed the relationship between the five hydrological factors and the respective spawning runs. Twenty-two years of continuous observations indicated that the daily mean values of all the five hydrological factors fluctuated within a certain range when CS was spawning. It was concluded that the optimal values for the hydrological factors during the spawning runs are 18.0–20.0°C for temperature, 14100 m³/s for discharge volume, 42.0–45.0 m for water level above the sea level, and 0.2–0.3 kg/m³ for silt content in the water, wherein the current velocity above the bottom layer to stimulate the fish to spawn should be between 1.0–1.7 m/s. The optimal water temperature might provide an essential precondition for other factors to trigger spawning. As water temperature reaches the optimal values and most of the other parameters are at the brink of deviation from their optimal range of values (water level, current velocity and silt content in the water), CS would begin to spawn. By 2009, when the Yangtze Three Gorges Project, which is located 45 km upstream of the Gezhouba Dam, is completed and begins to operate normally, changes in the downstream water temperature are expected to occur, which may have a negative effect on the development of gonad and the stimulation of spawning of CS; however, the anticipated decrease of the silt content in the water may be considered favorable for the performance of the spawning site.     

Cell culture and karyotype of Sakhalin sturgeon Acipenser mikadoi

A cell culture of rare and threatened species of Sakhalin sturgeon Acipenser mikadoi was established from a fragment of the pectoral fin and neighboring tissues. Initially, the culture consisted of different cell types including typical fibroblasts as well as cells of epithelial origin, myofibroblasts, etc. After approximately five passages, the culture largely consisted of cells with fibroblast morphology. Under normal culture conditions, these cells grew for more than one year at a constant rate and passed about 80 population doublings. In the absence of serum, cells entered the state of proliferative quiescence (G₀-state). When cultured without medium replacement for a long period of time, cells fused to form myofibers of about 1 cm in length. These myofibers could branch and acquired cross striation with time. About forty days after myofibers emerged, they degenerated, lost their shape, detached from the substrate, and finally died. The induction of adipogenic differentiation arrested cell proliferation and introduced lipophilic inclusions formed in a minor fraction of cells. The number of these inclusions was low, and cells with inclusions demonstrated various morphology distinct from typical adipocytes. The induction of osteogenic differentiation gave rise to cells that produce mineralized extracellular matrix and bone nodules. Chromosome analysis revealed a set of chromosomes typical for “high chromosome” sturgeon species. The variation in the chromosome number was very high (mean, 247 ± 33; modal value, 248). The analysis involving AT- and GC-specific fluorochromes has demonstrated that the telomeric and centromeric regions of all chromosomes are enriched in GC content. The distribution of AT- and GC-rich sequences along the chromosomes was heterogeneous. Long chromosomes were preferentially stained by the AT-specific dye, whereas small chromosomes demonstrated brighter fluorescence after 7-amino-actinomycin D staining; in particular, several small chromosomes fluoresced extremely brightly. This work is the first report of cell culture and karyotype analysis of Sakhalin sturgeon.     

人工养殖中华鲟幼鱼摄食不同饵料的转化效率与生长特性

利用水蚯蚓与人工饲料分别投喂7月龄中华鲟(Acipenser sinensis)幼鱼,研究不同饵料对中华鲟幼鱼转化效率与生长特性的影响.结果表明:经过60 d生长,水蚯蚓组、人工饲料组中华鲟幼鱼的平均体长分别从177.0、191.6 mm增至216.6、332.5 mm,体质量分别从32.73、44.39 g增至58.27、264.71 g;水蚯蚓组、人工饲料组中华鲟幼鱼的饵料转化率分别为6.67～39.33、0.89～1.26,特定生长率分别为0.19%～2.33%、1.38%～3.94%.生长效率分别为2.54%～14.99%、79.56%～204.44%;人工饲料组中华鲟幼鱼的生长速度快于水蚯蚓组,肥满度大于水蚯蚓组;2个试验组中华鲟幼鱼的体长与体质量均呈幂函数关系,各阶段幂指数b值均小于3,表明中华鲟幼鱼为异速生长;水蚯蚓组中华鲟幼鱼肌肉的水分湿质量含量为82.23%±0.79%,蛋白干质量含量为62.79%±1.34%,均略比人工饲料组高;综合饵料转化效率与各项生长指标,表明人工饲料比水蚯蚓更适宜作为中华鲟幼鱼阶段的人工养殖饵料.     

Fine structure and morphology of sterlet (Acipenser ruthenus L. 1758) spermatozoa and acrosin localization

Ultrastructure of sterlet Acipenser ruthenus L. 1758 sperm was examined by scanning and transmission electron microscopy, which allowed us to use various methods for visualizations of different parts of sterlet spermatozoa. Sperm cells possess a head with a distinct acrosome, a midpiece and a single flagellum surrounded by the flagellar plasma membrane. The average length of the head including the acrosome and the midpiece was estimated as 5.14+/-0.42 microm. Nine to 10 posterolateral projections were derived from the acrosome. Three inter-twining endonuclear canals bounded by membranes traversed the nucleus in its whole length from the acrosome to the implantation fossa. Acrosin was located in all the three parts (acrosome, endonuclear canals and implantation fossa). The proximal and distal centrioles located in the midpiece compacted of nine peripheral triplets of microtubules. One cut of the midpiece contained from two to six mitochondria with area of 215+/-85 nm(2) in average. The flagellum was 42.47+/-1.89 microm in length with typical eukaryotic organization of one central pair and nine peripheral pairs of microtubules. It passed through a cytoplasmic channel in the midpiece, which was formed by an invagination at the plasmalemma. The flagellum gradually developed two lateral extensions of its plasma membrane, so-called "fins". Detected morphological variation can be described by four principal component axes corresponding to groups of individual morphometric characters defined on the sperm structures. Correlations among the characters indicate that the sperms are variable in their shape rather than size. Significant variation among examined fish individuals was found only in flagellum and nucleus length. Comparison between the present and previous studies of morphology of sturgeon spermatozoa confirmed large inter- and/or intra-specific differences that could be of substantial taxonomic value.     

Parasites of lake sturgeon, Acipenser fulvescens (Chondrostei: Acipenseridae), from central Canada

Nineteen species of parasites were recovered from lake sturgeon, Acipenser fulvescens, from four major waterways of Central Canada; the Saskatchewan, Nelson, Winnipeg and Rainy River systems, Twelve of these are new host records. Host specific parasites, Crepidostomum auriculatum , Diclybothrium armatum , Spinitectus acipenseri and Truttaedacnitis clitellarius , forming the core parasite species, were recovered with the highest prevalence (≥70%) and were most widely distributed. Polypodium hydriforme was recovered from only stage IV sturgeon oocytes. With the exception of Pomphorhynchus bulbocolli , prevalence and intensity of endohelminth infections were not correlated with sex or age of host but the distribution of non host-specific parasites among sampling sites was determined by the type and relative abundance of food items consumed. The parasites of lake sturgeon are closely correlated to its diet and the species of parasites recovered are more similar to those of freshwater sturgeon in Eurasia than to other species of Acipenser in North America. The present parasite community of lake sturgeon appears to have been shaped by three major factors; the presence of core parasite species which predates geographic isolation, a benthic freshwater diet which has reshaped the parasite community to one comprising freshwater species and a long association with freshwater habitats which is reflected in the reproductive isolation of the lake sturgeon and lastly, the establishment of a host-specific parasite, Spinitectus acipenseri .     

Endangered migratory sturgeons of the lower Danube River and its delta

Historically, five acipenserid species migrated from the Black Sea into the Danube River: beluga Huso huso, Russian sturgeon Acipenser gueldenstaedtii, stellate sturgeon A. stellatus, ship sturgeon A. nudiventris, and perhaps European Atlantic sturgeon A. sturio. The freshwater sterlet A. ruthenus thrived in the Danube and its tributaries. Presently, only three anadromous species occur in the Romanian part of the Danube, Huso huso, A. gueldenstaedtii, and A. stellatus, while A. ruthenus lives in the Danube and its tributaries. Extreme depletion in the number of sturgeons was caused by many, primarily anthropogenic, factors which affected the Danube and the Black Sea shelf during recent last decades. Measures necessary for saving anadromous sturgeon species in the lower Danube are recommended.     

Present status of commercial stocks of sturgeons in the Caspian Sea basin

Catches for the last 25 years are analyzed for beluga Huso huso, stellate sturgeon A. stellatus and Russian sturgeon Acipenser gueldenstaedtii, which are the three commercially important species of sturgeons found in the Caspian Sea Basin. Population sizes for generations born between 1961 and 1970 are estimated, and found to depend on natural reproduction and the number of young fish stocked annually from sturgeon hatcheries located in the Volga River Delta. A ban on sea fishing from 1962 to 1991 positively impacted the number and total biomass of commercial stocks. Sturgeon growth rates depend on water levels in the Caspian Sea. In order to preserve Caspian Sea sturgeon populations, it will be necessary to coordinate efforts of all countries surrounding the Caspian Sea to achieve rational harvests, preserve juveniles, and produce at least 100 million juveniles annually from hatcheries.