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Summary Knowledge of the morphological properties, species specific differences, development, and function of the sturgeon egg envelope is of importance for a better understanding of sturgeon reproduction as well as for improvement of the caviar quality. The structure of the egg envelope is similar among the various species, comprising an external envelope (thecal cells, basal lamina, and follicular epithelium), a five-layered oocyte envelope (adhesive layer, alveolar layer, epilayer, and zona radiata externa and interna) and a layer of oocyte matrix and cortical granules. Egg diameters (1.5–4.9 mm), structure and number of the micropyles (2–52), and the size of the micropylar field distinguish eggs of the various species. The development of the egg envelope within the ovary comprises five stages, with further changes following fertilization with the formation of a fertilization cone. The mechanism of polyspermy block in sturgeon eggs and the role of the micropyle and cortical granules in polyspermy block are also described in this review. This review provides information on the morphology and the developmental stages of the egg envelope that will further the understanding of egg biology of acipenserid species. Standardization of terminology describing the egg envelope would minimize confusion and be helpful for future work on acipenserid eggs.

Summary Embryonic and larval development of the tench, Tinca tinca, is described, along with the origin and migration routes of germ cell lineage. Primordial germ cells (PGCs) potentially transmit genetic information to the next generation, and represent a powerful tool for creating a germ-line chimera within fish species. PGCs were identified by injecting synthesized mRNA, combining green fluorescent protein and the zebrafish nos1 3′UTR, under the blastodisc of embryos at the 1–4 cell stage. Developmental stages were divided into five periods defined by morphological features: cleavage (40 min–5 h post-fertilization (hpf), blastula (3.6–12 hpf), gastrula (12–20 hpf), segmentation (20–65 hpf), and hatching (65–188 hpf). The migration pathways of fluorescent PGCs were detected from 100% epiboly (18 hpf) to the end of the hatching period (184 hpf) in 69.3% of injected embryos, which migrated to the site of future gonads. Each hatching larva possessed 3–10 labeled PGCs with 95.1% of these cells localized at the genital ridge. These data may have use in practical aquaculture as well as in research to investigate germ-line chimerism in tench.

Summary Diploid spermatozoa were obtained from sex-reversed clonal diploid males and neo-tetraploid which derived from normal diploid × natural tetraploid cross followed by the 2nd polar body release inhibition. The spermatozoa from sex-reversed clonal diploid males exhibited a significant reduction in motility when compared with those from normal diploid and neo-tetraploid males. Electron microscopy revealed that diploid spermatozoa from sex-reversed clonal diploid and neo-tetraploid males exhibited normal shape similar to haploid spermatozoa from normal diploid males, except for larger sperm-head size and longer flagellum. Considering flow-cytometric results, volume of mitochondrial mass per spermatozoon was also increased in proportion to the elevation of ploidy status from haploid to diploid sperm. Diploid spermatozoa from neo-tetraploid increased the number of mitochondria and the ATP content, but those from sex-reversed clonal diploid males did not show such results.

Summary Physico-chemical properties (spermatozoa motility, spermatozoa concentration, seminal plasma protein concentration, osmolality, pH, ions) and sperm protein profiles were evaluated in three Acipenseriforme species [Siberian sturgeon (Acipenser baerii), sterlet (Acipenser ruthenus) and paddlefish (Polyodon spathula)]. The spermatozoa velocity was observed significantly highest in sterlet and lowest in Siberian sturgeon (P

Summary Siberian sturgeon Acipenser baerii is supposed to by species of functionally tetraploidy (4n). Large-scale screening of ploidy levels of various sturgeon stocks revealed one hexaploid (6n) male specimen producing triploid spermatozoa. Spermatozoa of three tetraploid individuals were compared with those of the hexaploid specimen in terms of ultrastructure and motility features. All evaluated morphometrical characteristics of the acrosome, the head, the midpiece and the flagellum showed significantly higher values in spermatozoa of 6n in comparison with 4n Siberian sturgeon males. Mean values of velocities at the beginning of activation differed highly significant between spermatozoa of 6n (155.19 and 158.22 μm s−1) and 4n males (181.05 and 179.21 μm s−1) in time 15 and 30 s post activation. Nevertheless their velocities did not show significant differences between spermatozoa of 6n (149.35 and 154.16 μm s−1) and 4n (158.00 and 152.66 μm s−1) in 30 and 45 s post activation. It was supposed that the bigger head of 6n male spermatozoa inhibited motility at the beginning of activation, but later the longer flagellum and bigger midpiece with higher number of mitochondria can partially balance the increased sizes of heads in spermatozoa movement of male with higher ploidy level.

Summary Sturgeon gametes are unique in that their spermatozoa possess acrosome containing acrosomal enzymes whereas their eggs are perforated by numerous micropyles. Thus the function of acrosome, which undergoes acrosomal reaction and filament formation, is unclear. The acrosomal reaction of sterlet Acipenser ruthenus spermatozoa was induced by sperm exposure to the solution containing Ca2+ and high pH. The rate of affected spermatozoa was evaluated using Soybean Trypsin Inhibitor-Alexa conjugate fluorescent staining. Fertilization and hatching test using sperm of this way disrupted acrosome and non-treated sperm as a control proofed necessity of acrosome integrity for fertilization. Increasing percentage of spermatozoa with disrupted acrosome highly decreased percentage of hatching, in spite of electron microscopy verification that the spermatozoa bearing such disrupted acrosomes were able to reach the micropyle. In addition the significant positive correlation between the ability of spermatozoa to induce acrosomal reaction by activation solution and sperm fertilizing ability suggested that spermatozoa, which are able to activate the acrosomal reaction, are more successful in fertilization.

Summary Morphology and fine structure of Barbus barbus L 1758 spermatozoa were studied using scanning (SEM) and transmission (TEM) electron microscopy. The results confirm that spermatozoa exhibit morphological features typical to all teleost fishes. They are differentiated into a head, a midpiece and a flagellum with the typical ‘9 + 2’ pairs of microtubules. Both dynein arms are present in the flagellum. The spermatozoa have spherical nuclei, 4–6 mitochondria located in the postnuclear cytoplasmic region and centriolar complex (proximal and distal centrioles). Total length, head width, length of midpiece and length of flagellum were measured to be 56.35 ± 7.42, 1.80 ± 0.06, 0.48 ± 0.14 and 54.30 ± 6.97 μm, respectively. Highly significant linear correlation was observed between posterior and anterior width of midpiece (P

Summary The present study was carried out with two sturgeon species, Siberian sturgeon (Acipenser baerii) and sterlet (A. ruthenus) to compare spermatological parameters to better understand inter-species differences. Significant differences between morphometric features were observed such as acrosome length, acrosome width, head length, midpiece width and flagellar length, while midpiece length did not reveal such differences. The sterlet has a shorter spermatozoon than the Siberian sturgeon. Ultrastructural parameters vary significantly in terms of length of the nucleus, diameter of the endonuclear canals (EC), size of posterolateral projections (PP) and diameter of flagellum. Mean values for density of spermatozoa in the semen, seminal plasma pH, osmolality (mOsmol kg−1), along with Ca2+, Na+, K+, Cl− ions concentrations (mm) were determined to be 0.61 ± 0.37 × 109, 8.16 ± 0.18, 77.20 ± 52.28, 0.24 ± 0.06, 31.39 ± 10.21, 3.51 ± 1.10, 14.00 ± 4.30 in A. baerii and 0.41 ± 0.32 × 109, 8.13 ± 0.19, 50.74 ± 6.27, 0.16 ± 0.11, 20.11 ± 3.78, 1.26 ± 0.54, 6.11 ± 0.60 in A. ruthenus, respectively. Significant differences were observed in Na+, K+ and Cl− concentrations in the seminal plasma as well as in sperm velocity. The percentage of motile spermatozoa did not show any significant difference between the two species. Comparing the results of this study with published literature data on sturgeon spermatozoa reveals that morphological and ultrastructural parameters of spermatozoa together with some parameters of the seminal fluid and spermatozoa velocity can be used in comparative spermatology to better understand inter-species differences. The observed biochemical and physiological differences should be also considered for the development of methods for controlled reproduction and for sperm cryopreservation techniques.

Summary Trypsin-like activity, similar to acrosin, is present in sturgeon spermatozoa and can be a potential target for trypsin inhibitors. The objective of this work was to use a fluorescent soybean trypsin inhibitor (SBTI) conjugate with the Alexa Fluor® 488 dye for visualization of the sturgeon acrosome. After incubation with SBTI-Alexa, a strong signal was observed both in the acrosome and midpiece or implantation fossa region. We have also found that SBTI-Alexa staining can be combined with PI viability test. Detailed examination of staining pattern revealed that SBTI-Alexa can stain either acrosome or whole sperm. Staining of whole sperm correlated with dead staining (r2 = 0.94, P