Ultrastructure and morphology of spermatozoa in Chinese sturgeon (Acipenser sinensis Gray 1835) using scanning and transmission electron microscopy

The Chinese sturgeon (Acipenser sinensis Gray 1835) is an endangered anadromous sturgeon inhabiting the Yangtze River in China. In this study, the ultrastructure and morphology of spermatozoa was studied using transmission and scanning electron microscopy with a cryo-holder. The spermatozoon consisted of an elongated head with a distinct acrosome and nucleus region, a midpiece and a flagellum. The mean length of the head and midpiece, the flagellum and total length of spermatozoon were 4.48, 33.3 and 37.8 microm, respectively. The nucleus was an elongated trapezoid shape with anterior (acrosome) end narrower than the posterior. Granular material and an actin filament were observed within the anterior acrosome. Three to five endonuclear canals were present. The midpiece was eudipleural along its longitudinal axis. Compared to other sturgeon species, the data from the present study suggest a more recent evolutionary linkage between Chinese sturgeon and white sturgeon (Acipenser transmontanus Richardson 1836).     

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.     

The ultrastructure of amberjack (Seriola dumerilii) sperm

Scanning and transmission electron microscopy were used to investigate the fine structure of sperm of the Mediterranean amberjack Seriola dumerilii. Each spermatozoon has an ovoid head which lacks an acrosome, a short, irregularly-shaped midpiece and a long flagellar tail. The midpiece houses eight spherical mitochondria, which are separated from the axoneme by the cytoplasmic canal. The centrioles are arranged approximately at right angles to each other. The proximal centriole lies inside, and the distal centriole outside, the nuclear fossa. The flagellum is inserted eccentrically into the head and is tangential to the nucleus, so that the spermatozoon is asymmetrical. It contains the conventional 9 + 2 axoneme, shows intratubular differentiations in the A microtubules of doublets 1, 2, 5 and 6, and possesses one pair of lateral fins. On the basis of its ultrastructural organization, the amberjack sperm resembles type II sperm as defined previously, except for the presence of the proximal centriole inside the nuclear fossa. This could result from a partial rotation of the nucleus during spermiogenesis.     

Spermiogenesis and fine structure of the spermatozoon in a headstander, Chilodus punctatus (Teleostei, Characiformes, Anostomidae)

The main characteristic features of spermiogenesis in Chilodus punctatus (Characiformes) are rotation of the nucleus, development of a nuclear fossa, which extends as a narrow invagination deep into the nucleus and the way in which flagellum is formed. The chromatin condensation proceeds during the spermiogenesis from heterogeneous through homogenous and granular to a highly compact one present in the mature spermatozoon. Mature Ch. punctatus spermatozoon shows a spherical nucleus, short midpiece and flagellum with lateral fins. The centrioles are in perpendicular arrangement and are located in the deep nuclear fossa, which extends towards the anterior pole of the nucleus. The midpiece contains a few mitochondria, which are separated from the anterior fragment of flagellum by the cytoplasmic channel. Spermiogenesis and spermatozoon ultrastructure conform to the pattern observed in other ostariophysans, but for the first time the presence of lateral fins along flagellum has been documented in a representative of Characiformes.     

Morphology and ultrastructure of Siberian sturgeon (Acipenser baerii) spermatozoa using scanning and transmission electron microscopy

BACKGROUND INFORMATION: Available data concerning the sperm morphology of teleost fishes demonstrate wide variation. In the present study, the spermatozoa of Siberian sturgeon (Acipenser baerii Brandt, 1869), a chondrostean fish, was investigated. In contrast with teleost fish, chondrostean spermatozoa have a head with a distinct acrosome, whereas other structures, such as a midpiece and a single flagellum, are present in spermatozoa of most species. RESULTS: The average length of the head including the acrosome and the midpiece was 7.01+/-0.83 microm. Ten posterolateral projections derived from the acrosome were present on a subacrosomal region, with mean lengths of 0.94+/-0.15 microm and widths of 0.93+/-0.11 microm. The nucleus consisted of electrodense homogeneous nuclear chromatin. Three intertwining endonuclear canals, bound by membranes, traversed the nucleus longitudinally from the acrosomal end to the basal nuclear fossa region. There were between three and six mitochondria, two types of centrioles (proximal and distal) in the midpiece and two vacuoles composed of lipid droplets. The flagellum (44.75+/-4.93 microm in length), originating from the centriolar apparatus, had a typical 9+2 eukaryotic flagellar organization. In addition, there was an extracellular cytoplasm canal between the cytoplasmic sheath and the flagellum. CONCLUSIONS: A principal components analysis explained the individual morphological variation fairly well. Of the total accumulated variance, 41.45% was accounted for by parameters related to the head and midpiece of the sperm and the length of the flagellum. Comparing the present study with previous studies of morphology of sturgeon spermatozoa, there were large inter- or intra-specific differences that could be valuable taxonomically.     

Fine structure of spermatozoa in the common pandora (Pagellus erythrinus Linnaeus, 1758) (Perciformes, Sparidae)

Scanning and transmission electron microscopy were used to investigate the fine structure of the sperm of the Sparid fish Pagellus erythrinus L. The spermatozoon of pandora has a spherical head lacking an acrosome, a cone-shaped midpiece and a long tail. The midpiece houses a single mitochondrion. The centriolar complex lies inside the nuclear fossa and is composed of a proximal and a distal centriole which are arranged at right angles to each other. The flagellum is inserted medio-laterally into the head, contains the conventional 9+2 axoneme and possesses one pair of lateral fins. On the basis of its ultrastructural organization, the pandora sperm can be regarded as an evolved form of the primitive spermatozoon found in Teleosts. According to the morphological classification proposed by Mattei (1970), the sperm of pandora belongs to a "type I" designation, like that of the other Sparid fish.     

Ultrastructure of grey mullet (Mugil cephalus,Linnaeus, 1758) spermatozoa as revealed from light,scanning and transmission electron microscopy

Spermatozoa morphology and fine structure were studied in the grey mullet, Mugil cephalus using light, scanning and transmission electron microscopy. Light microscopy observations indicate a semi‐cystic type of spermatogenesis in the testis. The electron microscopy micrograph showed that the spermatozoon of M. cephalus is uniflagellated (total length 5.78 ± 1.26 μm), differentiated into an ovoid‐shaped head without acrosome (1.80 ± 0.35 μm in length and 1.91 ± 0.30 μm in diameter), with a short midpiece and a long cylindrical flagellar tail (length 3.60 ± 0.50 μm). The midpiece is characterized by the presence of four to five vacuoles, a cytoplasmic canal, two centriole and two spherical mitochondria having a flat type of cristae. Chromatin granules of the nucleus form an electron‐dense homogeneous mass. The flagellum consists of nine peripheral microtubules and a central pair (9 + 2) surrounded by the plasma membrane with side fins. The results confirm that spermatozoa of M. cephalus are perciform or teleostean type II. Information generated from the present study will be useful in taxonomic classification, cryopreservation and breeding work.     

An Ultrastructural Study of the Spermatozoa from Prionospio cf. queenslandica and Tripolydora sp.: Two Spionid Polychaetes with Different Reproductive Methods

The fine structure of the spermatozoa of two spionids is described. The spermatozoon of Prionospio cf. queenslandica is typical of an animal utilizing external fertilization, in having a subspheroidal nucleus, a midpiece composed of unmodified rounded mitochondria surrounding two centrioles and a free flagellum. The acrosome is unusual in showing bilateral symmetry. The spermatozoon of Tripolydora sp. resembles that of spionids utilizing spermatophores, in possessing an extremely elongate nucleus and midpiece. The nucleus is penetrated by the 9+2 axoneme for its entire length, linking with a single centriole at the anterior end. Platelets surround the nucleus and intermingle with the mitochondria of the midpiece, which terminates with an annulus. The acrosome shows some internal vesiculation and substructuring. Sperm structure in relation to reproductive methods is discussed and the view of external fertilization as primitive is questioned.     

Ultrastructural study of spermatozoa of the paddlefish, Polyodon spathula

Paddlefish, Polyodon spathula, spermatozoa were examined by transmission electron microscopy. Their structure has the same characteristic architectural features as sturgeon spermatozoa. Paddlefish spermatozoa are of the primitive type and consist of a rod-shaped head, a midpiece and a long flagellum. The head is about 5.15 mm in length and contains the nucleus and an apical acrosomal complex. Inside the nucleus there are three nuclear channels that begin in the subacrosomal area and have a triple helical arrangement. An nuclear fossa is present centrally, at the posterior end of the nucleus. The midpiece contains a pair of centrioles in a perpendicular arrangement, mitochondria and a narrow cytoplasmic sleeve. The flagellum has a central axoneme with a 9 + 2 pattern and two lateral projections or fins.     

Fine structure of spermatozoa in the gilthead sea bream (Sparus aurata Linnaeus, 1758) (Perciformes, Sparidae)

Scanning and transmission electron microscopy were used to investigate the fine structure of the sperm of the sparid fish Sparus aurata L. The mature spermatozoon of gilthead sea bream belongs, like that of the other sparid fish, to a "type I" as defined by Mattei (1970). It has a spherical head which lacks an acrosome, a short, irregularly-shaped midpiece and a long cylindrical tail. The nucleus reveals a deep invagination (nuclear fossa) in which the centriolar complex is located. The two centrioles are approximately perpendicular to each other and show a conventional "9+0" pattern. The proximal centriole is associated with a cross-striated cylindrical body lying inside a peculiar satellite nuclear notch which appears as a narrow invagination of the nuclear fossa. The distal centriole is attached to the nuclear envelope by means of a lateral plate and radial fibres made of an electron-dense material. The short midpiece houses one mitochondrion. The flagellum is inserted perpendicularly into the base of the nucleus and contains the conventional 9+2 axoneme.     

Fine structure of spermatozoa of Chondrostoma nasus and Rutilus meidingerii (Teleostei, Cyprinidae), as revealed by scanning and transmission electron microscopy

Fürböck, S., Patzner, R.A. and Lahnsteiner, F. 2008. Fine structure of spermatozoa of Chondrostoma nasus and Rutilus meidingerii (Teleostei, Cyprinidae), as revealed by scanning and transmission electron microscopy. — Acta Zoologica (Stockholm) 91 : 88–95
The fine structure of spermatozoa of sneep or nase, Chondrostoma nasus , and lake chub, Rutilus meidingerii , was investigated by means of scanning and transmission electron microscopy. The uniflagellate spermatozoa of C. nasus lacked an acrosome. The flagellum contained the conventional nine peripheral doublets and one central pair of microtubules (9 + 2 pattern) and lacked lateral fins. The uniflagellate spermatozoa of R. meidingerii were made up of a head, also without an acrosome. For both species the sperm tail was covered by a plasma membrane. The midpiece of C. nasus contained five or six mitochondria on average, vesicles and glycogen granules, whereas the midpiece of R. meidingerii had seven mitochondria of a spherical or ovoid shape. The centriolar complex was located caudolaterally with respect to the nucleus. In C. nasus , the centrioles were orientated at an angle of 125° to each other, whereas the centrioles of R. meidingerii were at an angle of 110°. The fine structure of C. nasus and R. meidingerii spermatozoa showed species-specific differences in the position of the proximal centriole relative to the distal centriole, the position and number of mitochondria, size of the head and the length of the flagellum. (Correction added on 11 June 2009, after first online publication: The word 'axoneme' was deleted from the sentence 'The flagellum contained the conventional nine peripheral doublets and one central pair of microtubules (9 + 2 pattern) axoneme and lacked lateral fins.')     

Spermatozoa morphology and ultrastructure in Nile perch,Lates niloticus (Linnaeus, 1758)

Lates niloticus is a valuable commercial fish species with good potential for aquaculture. However, there is limited information on the type and structure of the Nile perch spermatozoon, which could potentially aid in culture of this species. Here, we describe the spermatozoon ultrastructure in L. niloticus using transmission and scanning electron microscopy. The spermatozoon had a round head-shape, medio-laterally flat, no acrosome, a short midpiece located laterally to the nucleus, uniflagella with one wing. The head of the spermatozoon contained the nucleus, centriolar system, proximal part of the flagellum, and cytoplasmic channel. Centrioles were arranged at an angle of 90° to each other, forming a T-shape, parallel to the nucleus. The midpiece was cylindrical, loaded with cytoplasm, five to seven spherical mitochondria; and the flagellum’s plasma membrane extended to form one lateral wing. The spermatozoa were classified as type II spermatozoa. L. niloticus spermatozoon differed from that of its Australian congener L. calcarifer, especially in the centriole arrangement and nuclear shape, length of the midpiece and the number of mitochondria and lateral wings.     

An ultrastructural study of spermiatogenesis and spermatozoal morphology in Sparganophilus tamesis (Sparganophilidae, Oligochaeta, Annelida)

Spermatogenesis in Sparganophilus tamesis results in a filiform spermatozoon of the advanced type. Structures in proximal-distal sequence are the slender acrosome, the extremely elongate nucleus, the short cylindrical midpiece and the long flagellum. The acrosome is unique in those Lumbricina so far studied in persistence of the subvesicular space in the anterior (proximal) bulb formed by the primary acrosome vesicle, external to the acrosome tube and in extension of the acrosome rod into this proximal subvesicular space. A further unusual feature is the very long basal chamber in the acrosome tube, distal to the rod, as in the Phreodrilidae. The acrosome tube has a distal limen and its junction with the nucleus is domed. There is little similarity with the acrosome of the Lumbricidae, a family with which the Sparganophilidae have recently been grouped. The midpiece has the highest number of mitochondria yet recorded for oligochaetes. The number is deduced to be eight, of which seven are normally visible in cross section because one of the mitochondrial loci consists, uniquely for the Oligochaeta, of two mitochondria aligned longitudinally in tandem. The structure of the flagellum, including the arrangement of its peripheral glycogen granules, is typical for oligochaetes. The spermatozoon is straight, lacking a spiral coil or keel. These results are discussed in relation to oligochaete phylogeny.     

圆斑星鲽精子的超微结构及核前区特殊结构

分别以扫描电镜和透射电镜方法研究了圆斑星鲽 (Veraspervariegates)精子的超微结构。头部呈圆形、中段不发达 ,具有多个未分化的圆形小线粒体、鞭毛结构极简单 ,具有 9 2型的轴丝等特征 ,均表示圆斑星鲽的精子属于简单的原始类型 ,与多数其它高等鱼类精子结构相似。但是 ,圆斑星鲽精子核前部的凹陷 ,即不含染色质的电子透明区 ,以及核前区的囊泡结构却未见在其它新鳍鱼类精子中报道。圆斑星鲽精子核前凹陷开口于核前端稍偏处 ,凹陷呈不规则状 ,可深入到核的中央。凹陷处与染色质区无界膜分隔。凹陷区的前部及其开口处常有多个小的具单层界膜的囊泡 ,有时可见在凹陷区的开口处汇集成一个大泡。在某些处理过程中 ,例如在冷冻 -解冻过程中 ,囊泡可能丢失 ,而在精子顶端留下一个凹坑。尽管顶体在现存最早的新鳍鱼类 ,如雀鳝鱼及弓鳍鱼中已经完全消失 ,但考虑甚至在某些纯真骨鱼 ,如鲑形目中的螈鱼精子上 ,顶体仍然存在 ,而在其它一些纯真骨鱼精子或精子细胞中也存在顶体或顶体遗迹等事实。我们推测在圆斑星鲽精子中的上述特殊结构也是顶体的一种遗迹 ,但也不排除其是向外释放核内物质的一种途径的可能性     

The ultrastructure of spermiogenesis and spermatozoa in Diplomystes mesembrinus

Spermiogenesis in Diplomystes mesembrinus , one of the most primitive species from the Siluriformes, occurs in cysts. Differentiation of spermatids is characterized by chromatin compaction, flagellum development, nuclear fossa formation, rotation of the nucleus, and excess cytoplasm elimination. The spermatozoon head is round, the nucleus contains highly condensed chromatin clusters, the midpiece is short, the axoneme shows a 9 +2 pattern with two discrete lateral projections, and the acrosome is absent. The nuclear fossa penetrates deeply into the nucleus, including the centriolar complex and the start of the axoneme. The single large C-shaped mitochondrion surrounds the initial segment of the axoneme. The structural features of D. mesembrinus spermatozoon are similar to the Clupeiformes.     

Spermiogenesis and sperm ultrastructure in Cichla intermedia with some considerations about Labroidei spermatozoa (Teleostei, Perciformes, Cichlidae)

Spermiogenesis and spermatozoal structure were studied in Cichla intermedia, a primitive species of Neotropical Cichlids. The analysis shows that spermiogenesis is characterized by chromatin compaction, flagellum development, nuclear rotation, nuclear fossa formation and residual cytoplasm elimination. In the spermatozoa, the head is round, the nucleus contains highly condensed filamentous clusters of chromatin and an acrosome is absent. The nuclear fossa is slightly eccentric and shows a projection that penetrates into the nuclear outline. The proximal centriole is located in the initial segment of the nuclear fossa. The midpiece and the cytoplasmic channel are long. The mitochondria, about 10 in number, are round or slightly elongated, disposed in two layers around the initial segment of the flagellum. The flagellum has a classical 9+2 axoneme and two lateral fins. The data available show that no characteristics of spermiogenesis or spermatozoa are exclusively found in members of the suborder Labroidei. However, three characteristics seem to be exclusively observed in Cichlidae: (1) compact filamentous clusters of chromatin; (2) slightly eccentric nuclear fossa; and, (3) number of mitochondria.     

黄颡鱼(Pseudobagrus fulvidraco)精子的超微结构

黄颡鱼精子由头部、中段和鞭毛(尾部)三部分组成。头部的主要结构是细胞核。核中浓缩了的染色质呈颗粒状。染色质中有核泡存在。核泡中有致密颗粒状物。植入窝里井状,从核后端往前深陷入核的中央。中段的中心粒复合体位于植入窝中,结构独特。近端中心粒和基体首尾相对,排在同一直线上。某些精子的近端中心粒的中央腔中能见到一、二个粗大的颗粒状物。基体的中央腔中有一对中央微管。近端中心粒和基体之间有中心粒间体将两者隔开。中段的袖套连接于细胞核之后,其中分布着线粒体和一些囊泡。近袖套内膜处的细胞质中有一层膜与袖套内膜平行。鞭毛细长,其起始端位于袖套腔中。鞭毛上长有两排侧鳍。侧鳍呈波纹状,分居轴丝两侧,大致与轴丝的两条中央微管同在一个平面上。侧鳍的基部有囊泡。     

Sperm biology and control of reproduction in sturgeon: (II) sperm morphology, acrosome reaction, motility and cryopreservation

In the present review, sperm morphology, acrosome reaction, motility, short-term storage and cryopreservation are summarized and discussed in sturgeon (Chondrostei, Acipenseriformes). The elongated head of spermatozoon comprises an acrosome with 8?C12 posterolateral projections. Usually three endonuclear canals are observed in the nucleus. Proximal and distal centrioles and 3?C6 mitochondria are located in the midpiece region. The flagellum consists of an axoneme with a typical ??9?+?2?? structure of microtubules and presents a ribon-like structure due to two lateral membranous fins. Egg water, Ca²⁺ and Mg²⁺ can trigger acrosome reaction. Trypsin- and chymotrypsin-like activities are reported in sturgeon sperm. These physiological properties of sturgeon sperm are identified as serine activity with 33?kDa molecular mass and can be inhibited by their respective inhibitors. The K⁺ prevents sperm activation in seminal plasma, and hypo-osmolality or decrease of extracellular K⁺ triggers sperm activation. Extracellular Ca²⁺ is involved in flagellar beating pattern and sperm velocity. After activation, sperm motility, velocity, and flagellar beating frequency, wavelength and amplitude decrease, while number of waves and curvature increase. Sturgeon sperm can be stored for several days at 4?°C; however it is better to add K⁺ into the immobilizing medium because it prevents sperm activation during incubation. Regarding sperm cryopreservation, methanol is a better cryoprotectant than DMSO. Either short-term storage or cryopreservation of sperm generates damage to spermatozoa that lead to reduction of sperm motility performance. Some studies suggest using an activation medium containing Ca²⁺ for enhancing sperm motility performance of incubated or frozen-thawed sperm.