Using machine learning algorithms to analyse the scute structure and sex identification of sterlet Acipenser ruthenus (Acipenseridae)

Sturgeons are valued as specialty black caviar, which is very expensive. Only females are used in the technology of caviar aquaculture. Universal method of sex determination has not yet been developed. Most of known methods are not sufficiently accurate, or used at a relatively late age, or difficult to use. Perfect early determination of sex is considered to be impossible. Because of the dark colour of most sturgeons and important morphological differences, which fish of almost all ages have, were overlooked. We first found that the scute structure of sterlet sturgeon depends on the sex. The found dependencies with the help of machine learning algorithms open a possibility for creation of sex determination equipment using the artificial intelligence. Our results open a perspective for creation of sex determination methods for other 23 sturgeon species, which can increase the efficiency of caviar aquaculture and restoration of sturgeons in natural waters.     

History,current status and prospects of sturgeon aquaculture in Russia

Since natural sturgeon populations have drastically declined, aquaculture of these valuable fish is important to meet the ever‐increasing demand for meat and caviar, thereby reducing the pressure on natural sturgeon resources. There are two directions in sturgeon aquaculture: controlled propagation for release and commercial farming. The controlled propagation supports the conservation of natural fish populations, while the commercial cultivation of sturgeons supplies the needs of the consumer market with the delicacy production of caviar (mainly). This review deals with the current status of the controlled propagation and stocking in the Volga‐Caspian basin and the commercial farming of sturgeons in Russia. The article also investigates the management of farmed broodstocks of sturgeons, which are used for obtaining seedlings and caviar. It is for sure that the active and continuous development of the two directions of sturgeon aquaculture will allow preserving these unique ancient fish on our planet until natural populations can be re‐established by self‐sustaining populations.     

我国鲟鱼籽酱加工产业化开发

随着我国鲟鱼养殖规模的扩大,加强鲟鱼深加工产品开发,拓展产业链,优化产业结构,成为鲟鱼产业发展的必由之路。鱼籽酱作为鲟鱼加工的主要产品,加快实现其规模化生产将是我国鲟鱼产业升级的重要方向。本文在阐述全球鲟鱼籽酱产业现状的基础上,着重分析了我国鲟鱼籽酱加工研究及其产业化前景,总结了其中存在的主要问题,并提出了相应的对策。     

施氏鲟精巢和卵巢差减cDNA文库的构建和差异表达EST的筛选

应用抑制差减杂交（SSH）技术构建了施氏鲟（Acipenser schrenckii）精巢和卵巢组织的SMART cDNA文库及其cDNA差减文库，从两个差减文库中随机挑取200个克隆进行PCR检测，随机挑选其中的123个cDNA克隆测序。将所测序列经GenBank检索和生物信息学比较，发现有55个cDNA片段序列在GenBank上无明显的同源性，68个片段与已报道的基因有较高的同源性，其中17个cDNA片断为精巢中特异表达的基因，而51个为卵巢中特异表达的基因。精巢中大量表达的主要为延长因子（EF-1）和脂肪酸连接蛋白等与精子生成发育有关的基因，而卵巢主要为ZPC、组蛋白和周期蛋白等与卵细胞发育成熟相关的基因。这些EST数据为进一步筛选和克隆鲟鱼性腺组织特异性表达基因提供了材料平台，为鲟鱼基因组数据增补了大量信息。     

鲟鱼子酱的生产与国际贸易概况

简要介绍近些年世界鲟鱼子酱的生产及贸易情况,以及我国鲟鱼子酱的生产品种、产量、价格及贸易等情况;分析和预测我国养殖鲟鱼子酱产业的前景,为我国鲟养殖产业的有序持续发展提供参考。     

Allelic segregation of sex‐linked microsatellite markers in Nile tilapia (Oreochromis niloticus) and validation of inheritance in YY population

Stocking of all‐male fingerling produced by direct administration of male hormone 17‐α‐methyltestosterone is the most preferred method for present‐day aquaculture of the Nile tilapia Oreochromis niloticus. However, due to the growing concern of negative impact of steroid hormone in food fish, production of ‘genetically male’ tilapia, which depends on the concrete and thorough understanding of sex determination, has long been a scientific curiosity. The objective of the present study was to identify reliable sex‐linked markers and to evaluate the applicability of those markers in terms of monosex production approach. ‘XY’ neofemales were produced by using synthetic oestrogen and identified through selective breeding and progeny testing. Three females with progeny not deviating from 3:1 sex ratio (male:female) were designated as ‘XY’ neofemales and were used subsequently to produce putative YY progeny. Among the fifteen microsatellite markers tested, marker ARO172 was most informative in differentiating male and female genotypes. Twenty‐seven F₂ fish from three families were identified as putative YY males based on marker genotyping, and four of them were crossed to produce F₃ to validate marker association by progeny testing. The YY males produced 86%–100% male progeny indicating ARO172 a unique sex‐linked marker applicable in marker‐assisted selection.     

Use of endoscopy for gender and ovarian stage determinations in Russian sturgeon (Acipenser gueldenstaedtii) grown in aquaculture

The Russian sturgeon (Acipenser gueldenstaedtii) is native to the Caspian Sea, the Black Sea and the Azov Sea. It used to breed in the main incoming rivers, until dam construction in the mid 20th century blocked upriver spawning migration. Aquaculture of Russian sturgeon has only recently begun, prompted by their declining populations in natural habitats and the rise in meat and caviar prices. However, information on their gonadal development and puberty under culture conditions is incomplete.

Because sturgeons have no external sexual dimorphism and there are no external markers for sexing, internal examination of the gonads must be employed for gender identification as well as to monitor their development. The present study describes endoscopic and histological observations of the gonads of young Russian sturgeons aimed at identifying gender and monitoring ovarian developmental stage in females up to the age of 6 years, when they enter their first puberty cycle, as well as at 7 years of age, when they have completed vitellogenesis, under culture conditions. This information, as related to fish age and size, is of vital importance to commercial farming of Russian sturgeon for caviar production and reproduction.

For gonadal observations in both sexes, we used an endoscopic system consisting of a 4 mm, 14 cm long cystoscope sheath incorporated with fiber-optic light transmission, connected to a halogen cold light source and a miniature videocamera with a control unit attached to a color monitor. This system allowed us viewing of the fish's abdominal organs, and to save pictures of selected areas of the gonads on a computer as the fish's personal record. Ovarian biopsies were taken in parallel for histology at typical stages of gonadal development.

Gender could be identified with this system as early as at 3 years of age and the sex ratio under culture conditions of females, males and unidentified gender were 55, 40 and 5%, respectively.

Not only did large differences occur in the developmental stages of female of the same age group, but also ovarian development was highly asynchronous at the early vitellogenic stages. In late vitellogenesis, at the “gray egg” stage (1600–2600 μm diameter), the oocytes were quite regular in size and color, and remained so until the final stages of maturity.

Our study suggests that endoscopy is an efficient method for both gender identification at an early age, and for determination of gonadal development stage in sturgeon aquaculture. The ability to see the whole intact gonads of anesthetized fish can reveal important management and research information, with minimal damage or stress to the fish.     

Status, trends and management of sturgeon and paddlefish fisheries

The 27 extant species of sturgeons and paddlefishes (Order Acipenseriformes) represent a unique and relict lineage of fishes. Producers of coveted black caviar, sturgeons are one of the most valuable wildlife commodities on earth. The group is among the most endangered fishes with all species listed under Convention on International Trade in Endangered Species (CITES) Appendix I (two species) or II (25 species), only two species considered Lower Risk by IUCN, four of the nine US taxa and one Caspian species protected under the Endangered Species Act, and local extinctions recorded for 19 of 27 species. Despite their well‐publicized imperilled status, commercial pressure on 15 species persists. Here, after reviewing the biological characteristics of sturgeons and paddlefishes and their commercial use, an overview of global fisheries is presented. The synopsis demonstrates that, with few exceptions, sturgeon and paddlefish are imperilled across the globe and long‐term survival in the wild is in jeopardy. All major sturgeon fisheries have surpassed peak productivity levels, with 70% of major fisheries posting recent harvests <15% of historic peak catches and 35% of the fisheries examined crashing within 7–20 years of inception. Even in Caspian Sea fisheries, the most important globally, present catches are below 10% of historic peak landings. Improved domestic and international fisheries management and attention to habitat and species restoration is now needed. Although captive rearing offers promise for caviar alternatives and endangered species restoration, it must advance cautiously to avoid environmental harm. To ensure a continued supply of caviar and the survival of these unique fishes we offer recommendations for priority conservation action for the future.     

鱼类性别决定的遗传基础研究概况

动物从受精卵发育到具有不同性别特征的个体是一个奇妙而又严谨的过程,是人类长期以来试图揭示的自然现象。上世纪90年代初在人类Y染色体上发现了性别决定基因SRY[1],进而发现了一个新的Sox基因家族[2]。上述基因的发现,促进了以哺乳类为代表的动物性别决定和分化机制研究。由于鱼类在脊椎动物中的特殊进化地位、庞大的种类数量以及显著的社会经济价值,鱼类的性别决定研究一直受到遗传和发育学者的重视。尽管离最终阐明鱼类性别决定的机制还有距离,但近20多年来鱼类性别决定的遗传基础研究已取得不少重要进展。本文试图根据现有文献资料,…     

Sex steroid level and sexual dimorphism expression of genes in gonads of the great sturgeon Huso huso Linneaus, 1758 during maturity developmental stages

Little is known about molecular mechanisms involved in gonad differentiation in sturgeon species. In non‐mammalian vertebrates, sox9, dmrt1, cyp17a1 and ar are male specific genes in testicular differentiation and are highly conserved. In order to understand the mechanism underlying testicular development in sturgeon, we investigated sex steroids level of 11‐ketotestosterone (KT) and testosterone (T) and relative expression of sox9, dmrt1, cyp17a1 and ar in great sturgeon gonads during different stages of sexual maturity. The results showed all studied genes had dimorphic patterns in males. In immature gonads (stage I), only cyp17a1 expressed in male gonads, while other genes did not express, and KT and T levels were low. Dmrt1 showed dimorphic expression pattern in male gonads at maturity stage II, III and IV. Furthermore, sox9 and ar mRNA presented significant dimorphic expression pattern in male gonads only at maturity stage 4. Plasma androgens levels were significantly higher in males compared to females during maturity stages II, III and IV. The results showed that among these four genes, only cyp17a1 expressed in male gonads at maturity stage I (immature), suggesting that this gene may be applicable as a sex marker in recently differentiated male great sturgeon. Sexually dimorphic patterns in other studied genes (sox9, dmrt1 and ar) suggesting that these genes may be important for testicular development and differentiation in premature great sturgeon. The obtained results provide a foundation for further research on sex differentiation and developing strategies for the sexing of sturgeon for aquaculture.     

Identification of sex‐specific markers and heterogametic XX/XY sex determination system by 2b‐RAD sequencing in redtail catfish (Mystus wyckioides)

Sex‐specific markers provide significant molecular basis for sex control breeding biotechnology to produce all‐male or all‐female fish in commercial breeding. Redtail catfish (Mystus wyckioides), one of the commercial bagrid catfishes distributed in Southeast Asian, which have a long sexual maturation period that can last 3–5 years and males have apparent growth advantage over females, but its sex determination system remains unknown. In this study, we first applied 2b‐RAD‐seq approach to identify three male‐specific 2b‐RAD‐tags and one male heterogametic SNP locus and validated by blast to the genome survey sequences and PCR amplification in both wild and breeding populations. To get longer sex‐specific region, we performed genome walking and obtained a 4,630 bp of Y‐specific sequence and 4,581 bp of X‐specific sequence from the 2b‐RAD‐tag ref189950 with 92.19% nucleotide identity between them. And 9,923 bp/3,935 bp of Y‐specific sequences and 8,491 bp/5,172 bp of X‐specific sequences were also identified with 77.49% and 57.07% nucleotide identity in ref208528 and ref210837, respectively. Subsequently, three different kinds of sex‐specific primers with different length products were designed based on the detected highly sex differentiated regions and could be used to distinguish males and females both in wild and artificially bred populations. What is more, the X‐specific fragment was discovered to produce the dosage effect association in females and in males. The data suggest that male heterogametic XX/XY sex determination system should exist in the redtail catfish. More significantly, the sex‐specific markers are of great value to protect wild resources and improve the efficiency of all‐male breeding practices for aquaculture in the redtail catfish.     

Comparative analysis of reproductive performance between spring and autumn forms of Persian sturgeon,Acipenser persicus,Bordin, 1897: with an emphasis on sex steroids and milt quality

To compare the reproductive performance of spring and autumn forms of Persian sturgeon males, Acipenser persicus, the relative abundance of spermiating and non‐spermiating males, milt quality, sex steroids and cortisol were investigated after pituitary preparation (PP) treatment and at the time of spermiation. Our results showed that higher numbers of spring males are spermiated after PP treatment than autumn individuals. The autumn spermiating males had higher and lower values of sperm density and duration of motility than spring males respectively. The milt volume was higher in spring males than in autumn individuals. The percentage of motility was statistically equal in both the groups examined. In both forms of brooders, the serum levels of testosterone (T), 11‐ketotestosterone (11‐KT), progesterone (P), 17α, 20β, 21‐trihydroxy‐4‐pregnen‐3‐one (20βS) and cortisol (C) increased after PP treatment, although such increases did not occur in non‐spermiating males. Our results showed the probable involvement of 20βs, P, T, 11‐KT and C in the final maturation of Persian sturgeon. In addition, it was demonstrated that the spring form of Persian sturgeon shows better reproductive performance than the autumn form in terms of a response to artificial induction and milt quality.     

Study of sex determination system in ship sturgeon, Acipenser nudiventris using meiotic gynogenesis

The sex ratios and sex determination mechanism of gynogenetic diploids of ship sturgeon, Acipenser nudiventris, have been investigated to verify the possibilities of sex control by chromosome manipulation in this species. Meiotic gynogenesis was induced in a female ship sturgeon using cold shock after egg activation with UV-irradiated sperm of a male Siberian sturgeon. Microsatellite DNA analysis was applied for verification of uniparental inheritance in the gynogenetic diploid group of fish. All the analyzed gynogenetic diploids possessed only maternal genotype in the examined experimental group of fish. In this study, a minimum of two distinctly selected diagnostic loci in the offspring was used to confirm exclusively maternal contribution. Also, these fish were analyzed for sex diagnostic. Histological analysis of gonads from gynogenetic diploids, obtained from one family, showed 73.3 % of females and 27.7 % of males. The observed sex ratio has suggested that the ship sturgeon have a female heterogametic sex determination system. Gynogenesis in this species with female heterogametic sex determination system will have important role in breeding program and reclamation of its natural population to produce both female and male progeny, while this species has been introduced in the red list of IUCN (International Union for Conservation of Nature and Natural Resources).     

鱼类性别决定机制及相关基因研究进展

鱼类性别决定机制是脊椎动物中最复杂的。同高等脊椎动物一样,鱼类性别决定的基础依然是遗传基因。鱼类的性别控制对于水产养殖有着十分重要的指导意义。目前用于生产实践的鱼类人工性别控制方法有很多,但大多数仍然处于探索与实验阶段,理论上的作用机理仍未研究透彻。文章旨在通过对鱼类性别决定机制、性别决定相关基因等方面国内外研究进展的阐述,为鱼类性别控制、调控养殖鱼类的经济性状如生长率和个体大小等,提供有益的参考资料。     

Confirmation of ovarian homogeneity in post-vitellogenic cultured white sturgeon,Acipenser transmontanus

Assessing stage of oocyte maturity in female sturgeon by calculating oocyte polarization index (PI) is a necessary tool for both conservation propagation managers and caviar producers to know when to hormonally induce spawning. We tested the assumption that sampling ovarian follicles from one section of one ovary is sufficient for calculating an oocyte PI representative of oocyte maturity for an individual animal. Short-wavelength near-infrared spectroscopy (SW-NIR) scans were performed on three positions per ovary for five fish prior to caviar harvest. Samples of ovarian follicles were subsequently taken from the exact location of the SW-NIR scans for calculation of oocyte PI and follicle diameter. Oocyte PI was statistically different though not biologically relevant within an ovary and between ovaries in four of five fish. Follicle diameter was statistically different but not biologically relevant within an ovary in three of five fish. There were no differences in follicle diameter between ovaries. No statistical differences were observed between SW-NIR spectra collected at different locations within an ovary or between ovaries. These results emphasize the importance of utilizing both oocyte PI measurement and progesterone-induced oocyte maturation assays while deciding when to hormonally induce spawning in sturgeon females.     

中国鲟鱼产业技术研发现状与展望

2016年中国鲟鱼养殖产量89 773吨。鲟鱼种苗、饲料、养殖、加工及销售等环节的一些实用技术基本能满足鲟鱼产业的现实需要,但仍然存在不少问题,如种质退化问题、鱼子酱及鱼肉的品质问题、养殖过程中的氮磷排放问题。本文就中国已经形成的鲟鱼产业技术进行梳理、评述和展望。     

Male‐biased sex ratio of nonanadromous Oncorhynchus mykiss in a partially migratory population in California

Abstract – Differential rates of anadromy between males and females are common in partially migratory salmonid populations, but this pattern is not fully clear for Oncorhynchus mykiss (rainbow trout/steelhead) from the limited but mixed data available. In particular, there are very few data on sex ratios of juvenile and nonanadromous (resident) fish to help assess sex composition of various life stages and life‐history types. We used a recently developed Y‐chromosome genetic marker to assess sex ratio of stream‐dwelling (i.e., juvenile and nonanadromous) O. mykiss in a small coastal basin in central California, USA. We analysed 384 samples collected from three contiguous study reaches over 3 years. Sex ratio was 1:1 among juvenile‐sized O. mykiss (<150 mm) but highly male‐skewed (83%) among nonanadromous‐sized individuals (≥150 mm), and this sex ratio × size pattern did not differ among years or study reaches. Our results suggest that the rate of anadromy differs between males and females in this basin. Our study also demonstrates the application of new genetic markers to determine sex composition of immature and nonanadromous salmonids, which will help assess sex‐specific life‐history behaviour in partially migratory populations of O. mykiss and other species.     

Dimorphic expression of sex-related genes in different gonadal development stages of sterlet, <Emphasis Type="Italic">Acipenser ruthenus</Emphasis>, a primitive fish species

Molecular mechanism of sex determination and differentiation of sturgeon, a primitive fish species, is extraordinarily important due to the valuable caviar; however, it is still poorly known. The present work aimed to identify the major genes involved in regulating gonadal development of sterlet, a small species of sturgeon, from 13 candidate genes which have been shown to relate to gonadal differentiation and development in other teleost fish. The sex and gonadal development of sterlets were determined by histological observation and levels of sex steroids testosterone (T), 11-ketotestosterone (11-KT), and 17β-estradiol (E2) in serum. Sexually dimorphic gene expressions were investigated. The results revealed that gonadal development were asynchronous in 2-year-old male and female sterlets with the testes in early or mid-spermatogenesis and the ovaries in chromatin nucleolus stage or perinucleolus stage, respectively. The levels of T and E2 were not significantly different between sexes or different gonadal development stages while 11-KT had the higher level in mid-spermatogenesis testis stage. In all the investigated gonadal development stages, gene dmrt1 and hsd11b2 were expressed higher in male whereas foxl2 and cyp19a1 were expressed higher in female. Thus, these genes provided the promising markers for sex identification of sterlet. It was unexpected that dkk1 and dax1 had significantly higher expression in ovarian perinucleolus stage than in ovarian chromatin nucleolus stage and in the testis, suggesting that these two genes had more correlation with ovarian development than with the testis, contrary to the previous reports in other vertebrates. Testicular development-related genes (gsdf and amh) and estrogen receptor genes (era and erb) differentially expressed at different testis or ovary development stages, but their expressions were not absolutely significantly different in male and female, depending on the gonadal development stage. Expression of androgen receptor gene ar or rspo, which was supposed to be related to ovarian development, presented no difference between gonadal development stages investigated in this study whenever in male or female.     

鱼类性别决定的研究进展

有关鱼类性别决定的研究主要集中在温度、性激素、芳香化酶以及随机重复序列、核受体基因等对性别分化的调控方面。由于鱼类所处分类地位较低 ,生活环境千差万别 ,鱼类性别决定没有一个普遍的模式 ,目前研究的鱼类又各不相同 ,因此象哺乳动物那样的性别决定级联模式还没能阐述。本综述旨在阐述近几年有关鱼类性别决定机制方面的研究动态和进展 ,为系统研究鱼类性别决定机制提供参考     

Genetic, abiotic and social influences on sex differentiation in cichlid fishes and the evolution of sequential hermaphroditism

Genetic and environmental factors may interact to control sex determination in fishes. A common pattern of initial female differentiation and subsequent male transformation before maturation in non‐hermaphroditic fishes and after maturation in sequentially hermaphroditic fishes has suggested that changes in developmental timing may be responsible for the evolution of various expressions of sexual lability. Sequential hermaphroditism is rare in freshwater fishes, but investigators report degrees of sexual lability at four distinct life stages in cichlid fishes. Some cichlids undergo genetic sex determination and are not labile. Lability at the larval stage allows temperature or pH to determine sex. Social interactions apparently determine sex at the juvenile stage in the Midas cichlid (Amphilophus citrinellus). Most reports of post‐maturational sex change in cichlids are anecdotal or unsubstantiated. The common occurrence of same‐sex spawning suggests that many species are incapable of sex change. Sequential hermaphroditism is concluded not to be typical, except for the checkerboard cichlid (Crenicara punctulata), which regularly undergoes functional female‐to‐male transformation. Expression of sexual lability at four life stages in one family of fishes corroborates a role for developmental timing in the evolution of sequential hermaphroditism as well as environmentally controlled sex determination. The broad phylogenetic distribution of sexual lability in cichlids indicates that processes capable of producing sex change are generally present. The rarity of sequential hermaphroditism in cichlids and possibly other freshwater fishes is likely due to unpredictability of food and therefore potential mate distributions compared with coral reef habitats.