In vitro maturation of the potential for movement of carp spermatozoa

Common carp (Cyprinus carpio) sperm reduction during short-term in vitro storage at 4 °C

This study was designed to optimize a short-term storage protocol for common carp sperm at 4 °C under aerobic condition. Sperm from individual males were collected directly with or without extenders. The results demonstrated that in general, it was similar effect to collect sperm directly in extenders and keeping sperm for 0.5 h after collection without extenders. Sperm was diluted with eight selected extenders (sperm: extender = 2:1, 1:1 and 1:9) and undiluted sperm was used as a control. Sperm and seminal plasma parameters (sperm motility, velocity, membrane integrity, sperm concentration, osmolality and pH in seminal plasma) were evaluated in sperm stored on ice under aerobic conditions at 0, 2, 4, 6 and 8 days post stripping (DPS) using the computer- assisted sperm analysis system. Results showed that 1:1 and 2:1 dilution maintained higher sperm function and more sperm for a longer period. After 8 DPS, the best sperm quality and quantity was recorded in the common carp seminal plasma supplemented with 50 mM NaCl, Cejko extender (2 mM CaCl₂, 1 mM MgSO₄, 20 mM Tris, 110 mM NaCl, 40 mM KCl, pH 7.5 and 310 mOsm/kg) supplemented with/without 25 mM KCl/NaCl. The reduction of spermatozoa number with time during short-term storage but varied according to different dilution ratios and extenders. At 8 DPS, sperm count has dropped by 22.9 % in a dilution of 1:1 compared to 50.3 % in sperm without dilution. Extenders with diluted 1:1, especially Cejko solution, largely postponed sperm reduction, 21.3 % compared to 55.5 % for sperm stored without extenders.

Fish sperm motility analysis: the central role of the flagellum

Motility analysis of spermatozoa relies on the investigation of either head trajectories or flagellum characteristics. Those two sets of parameters are far from being independent, the flagellum playing the role of motor, whereas the head plays a passive role of cargo. Therefore, quantitative descriptions of head trajectories represent a simplification of the complex pattern of whole sperm cell motion, resulting from the waves developed by the flagellum. The flagellum itself responds to a large variety of signals that precisely control its axoneme to allow activation, acceleration, slowing down or reorientation of the whole spermatozoon. Thus, it is obvious that analysis of flagellum characteristics provides information on the original source of movement and orientation of the sperm cell and presents additional parameters that enrich the panoply of quantitative descriptors of sperm motility. In this review, we briefly describe the methodologies used to obtain good-quality images of fish spermatozoa (head and especially flagellum) while they move fast and the methods developed for their analysis. The paper also aims to establish a link between classical analyses by computer-aided sperm analysis (CASA) and the descriptors generated by fish sperm flagellum analysis, and emphasises the information to be gained regarding motility performance from flagellum motion data.

Sperm motility in fishes: (III) diversity of regulatory signals from membrane to the axoneme

Fish spermatozoa acquire potential for motility in the sperm duct where they are immotile. Osmolality of the seminal plasma is a key factor to maintain spermatozoa in the quiescent state in either freshwater or marine fishes. However, potassium (K⁺) ions prevent spermatozoa motility in salmonid and sturgeon fishes, while CO₂ inhibits spermatozoa motility in flatfishes. Once, spermatozoa are released at spawning, their motility is initiated in hypo-osmotic and hyper-osmotic environments in freshwater and marine fishes, respectively. Some substances produced by the testes (a progestin), or released from oocytes (peptides) induce spermatozoa hypermotility in some marine fishes including the Atlantic croaker and Pacific herrings, respectively. Duration of spermatozoa motility is short, lasting for a few seconds to few minutes in most fishes due to rapid depletion of energy required for the beating of the motility apparatus called axoneme. In the osmotic-activated spermatozoa, K⁺ and water effluxes occur in freshwater and marine fishes, respectively, which trigger spermatozoa motility signaling. In general, initiation of axonemal beating is associated with an increase in intracellular calcium (Ca²⁺) ions in spermatozoa of both freshwater and marine fishes and a post- or pre-increase in intracellular pH, while cyclic adenosine monophosphate (cAMP) remains unchanged. However, axonemal beating is cAMP-dependent in demembranated spermatozoa of salmonid and sturgeon fishes. Calcium from extracellular environment or intracellular stores supply required Ca²⁺ concentration for axonemal beating. Several axonemal proteins have been so far identified in fishes that are activated by Ca²⁺ and cAMP, directly or mediated by protein kinase C and protein kinase A, respectively. The present study reviews differences and similarities in complex regulatory signals controlling spermatozoa motility initiation in fishes, and notes physiological mechanisms that await elucidation.

Fish sperm biology in relation to urogenital system structure

Morphology of the urogenital system has evolved during fish speciation. Chondrostei (sturgeons and paddlefishes) possess an excretory system which is called "primitive" in that the sperm ducts enter the kidneys and share the excretory ducts where sperm is mixed with urine before it is released into the spawning environment. Further, in this group of fishes there are also physiological characteristics which are associated with these anatomical features where the mixing of sperm and urine is a prerequisite for the final sperm maturation rather than contamination. In the Holostei (gars and bowfins) which are closely related to the Chondrostei, sperm also naturally mixed with urine, but the physiological role of such mixing for sperm biology has not been described. In contrast, urinary and sperm ducts in the more evolved Teleostei are completely separate, and sperm and urine are not mixed before being released during spawning. Thus, urine constitutes an inappropriate environment which can be a source of problems when sperm is collected during fisheries practices. In this review, the consequences of such divergent conditions in the urogenital anatomy will be considered in relation to general features of fish sperm biology and in relation to aquaculture and fisheries practices.

Evaluation of seminal plasma composition and spermatozoa quality parameters of silver barb, Barbonymus gonionotus Bleeker, 1850

Seminal composition and semen quality are the important determinants in assessing the reproductive performance of different fishes. This study was carried out to evaluate the seminal composition and sperm quality of Barbonymus gonionotus. The seminal plasma contained 17.2 ± 0.34 mmol/l, 20.9 ± 0.48 mmol/l, 0.72 ± 0.04 mmol/l, 3.8 ± 0.2 mmol/l, and 1.49 ± 0.02 g/dl of Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, and total protein, respectively. The physical spermatological parameters, such as sperm volume, sperm motility, motility duration, sperm density, osmolality, and pH values were 1.55 ± 0.15 ml, 89 ± 2%, 391.9 ± 8.5 s, 2.8 ± 0.2 × 10¹⁰ /ml, 400.6 ± 5.1 mmol/kg, and 8.75 ± 0.10, respectively. In correlation matrix, the K⁺ (R² = 0.39, P < 0.01) and Ca⁺⁺ (R² = 0.27, P < 0.05) ions and osmolality (R² = 0.29, P < 0.05) showed significant positive correlations with sperm motility. Similarly, fertilization rate significantly influenced by sperm motility (R² = 0.26, P < 0.05) and K⁺ (R² = 0.30, P < 0.05) and Ca⁺⁺ (R² = 0.26, P < 0.05) ions. Also, osmolality significantly and negatively correlated with Mg⁺⁺ (R² = 0.33, P < 0.05) and sperm motility duration (R² = 0.28, P < 0.05). Therefore, based on this results, it can be concluded that seminal plasma ions, K⁺ and Ca⁺⁺ and osmolality are the key factors for the determination of sperm quality of silver barb, and these parameters could be considered during standardization of artificial fertilization or cryopreservation technique of silver barb spermatozoa.

Optimisation of sodium and potassium concentrations and pH in the artificial seminal plasma of common carp Cyprinus carpio L

The effect of sodium and potassium concentrations as well as optimal pH on the motility of common carp Cyprinus carpio L. sperm during short-term storage in artificial seminal plasma (ASP) was investigated. Sperm was collected from individual males (n = 5) and each sample diluted tenfold (1:9) in ASP (sperm:extender) containing 2 mM CaCl₂, 1 mM Mg₂SO₄ and 20 mM Tris at pH 8.0 and supplemented by the following concentrations of sodium and potassium (mM/mM): 0/150, 20/130, 40/110, 75/75, 110/40, 130/20 and 150/0. The osmolality of all ASP variants was set at 310 mOsm kg^-1. Sperm motility was measured using a CASA system during 72 h of storage. Immediately after dilution, sperm motility was high (90%) both in each variant and in the control group (fresh sperm). After 72-h storage, the highest sperm motility was noted in ASP containing 110 mM NaCl and 40 mM KCl. No differences were found in the motility of samples preserved within the pH range of 7.0-9.0. Our data suggest that for the short-term storage of common carp sperm, whereas the pH of the solution does not play a crucial role, a specific potassium concentration of around 40 mM is required.

Activation of free sperm and dissociation of sperm bundles (spermatozeugmata) of an endangered viviparous fish, Xenotoca eiseni

Knowledge of sperm motility activation for viviparous fishes has been limited to study of several species in Poeciliidae, and the dissociation of sperm bundles is even less understood. The goal of this study was to use the endangered Redtail Splitfin (Xenotoca eiseni) as a model to investigate the activation of sperm from viviparous fishes by study of free sperm and spermatozeugmata (unencapsulated sperm bundles). The specific objectives were to evaluate the effects of: (1) osmotic pressure and refrigerated storage (4 °C) on activation of free sperm, (2) osmotic pressure, ions, and pH on dissociation of spermatozeugmata, and (3) CaCl₂ concentration and pH on sperm membrane integrity. Free sperm were activated in Ca²⁺-free Hanks' balanced salt solution at 81-516 mOsmol/kg. The highest motility (19 ± 6%) was at 305 mOsmol/kg and swim remained for 84 h. Glucose (300-700 mOsmol/kg), NaCl (50-600 mOsmol/kg), and KCl, MgCl₂, and MnCl₂ at 5-160 mM activated sperm within spermatozeugmata, but did not dissociate spermatozeugmata. CaCl₂ at 5-160 mM dissociated spermatozeugmata within 10 min. Solutions of NaCl-NaOH at pH 11.6 to 12.4 dissociated spermatozeugmata within 1 min. The percentage of viable cells had no significant differences (P = 0.2033) among different concentrations of CaCl₂, but it was lower (P < 0.0001) at pH 12.5 than at pH between 7.0 and 12.0. Overall, this study provided a foundation for quality evaluation of sperm and spermatozeugmata from livebearing fishes, and for development of germplasm repositories for imperiled goodeids.

Changes to Extender, Cryoprotective Medium, and In Vitro Fertilization Improve Zebrafish Sperm Cryopreservation

Sperm cryopreservation is a highly efficient method for preserving genetic resources. It extends the reproductive period of males and significantly reduces costs normally associated with maintenance of live animal colonies. However, previous zebrafish (Danio rerio) cryopreservation methods have produced variable outcomes and low post-thaw fertilization rates. To improve post-thaw fertilization rates after cryopreservation, we developed a new extender and cryoprotective medium (CPM), introduced quality assessment (QA), determined the optimal cooling rate, and improved the post-thaw in vitro fertilization process. We found that the hypertonic extender E400 preserved motility of sperm held on ice for at least 6 h. We implemented QA by measuring sperm cell densities with a NanoDrop spectrophotometer and sperm motility with computer-assisted sperm analysis (CASA). We developed a CPM, RMMB, which contains raffinose, skim milk, methanol, and bicine buffer. Post-thaw motility indicated that the optimal cooling rate in two types of cryogenic vials was between 10 and 15°C/min. Test thaws from this method produced average motility of 20% ± 13% and an average post-thaw fertilization rate of 68% ± 16%.

Frenetic activation of fish spermatozoa flagella entails short-term motility, portending their precocious decadence

In most species, fish spermatozoa activate their motility on contact with the external medium (sea or fresh water depending of their reproductive habitat). Their flagella immediately develop waves propagated at high beat frequency (up to 70 beats s(-1)), which propel these sperm cells at high velocity (6-10 mm min(-1)), but for a quite short period of time, usually limited to minutes. Their specific inability to restore their energy content (mostly adenosine triphosphate) fast enough relatively to their high rate of energy consumption by flagellar contributes mainly to the activity arrest of motility, as the spermatozoa need to rely on early accumulated energy prior to activation. This review of the published data explains the present understanding of physico-chemical mechanisms by which flagellar motility is activated (mostly through osmotic and ionic regulation) and then propels sperm cells at speed. It aims also to describe the gradual arrest of their motility much of which occurs within a few minutes.

Marine fish spermatozoa: racing ephemeral swimmers

After a long period of spermatogenesis (several weeks to months), marine fish spermatozoa are delivered at male spawning in seawater (SW) at the same time as ova. In some fish species, as the ova micropyle closes quickly after release, these minute unicells, the spermatozoa, have to accomplish their task of reaching the micropyle within a very brief period (several seconds to minutes), for delivery of the haploid male genetic information to the ova. To achieve this goal, their high-performance motile equipment, the flagellum, must fully activate immediately on contact with the SW and then propel the sperm cell at an unusually high initial velocity. The cost of such 'hyperactivity' is a very rapid consumption of intracellular ATP that outstrips the supply. The spermatozoa become rapidly exhausted because mitochondria cannot compensate for this very fast flagellar energy consumption. Therefore, any spermatozoon ends up with two possibilities: either becoming exhausted and immotile or reaching the egg micropyle within its very short period of forward motility (in the range of tens of seconds) before micropyle closure in relation to both contact of SW and cortical reaction. The aim of the present review is to present step by step the successive events occurring in marine fish spermatozoa from activation until their full arrest of motility. The present knowledge of activation mechanisms is summarized, as well as a description of the motility parameters characterizing the motility period. As a complement, in vitro results on axonemal motility obtained after demembranation of flagella bring further understanding. The description of the sperm energetic content (ATP and other high energy compounds) and its evolution during the swimming period is also discussed. A general model aiming to explain all the successive cellular events occurring immediately after the activation is presented. This model is proposed as a guideline for understanding the events governing the sperm lifespan in the marine fish species that reproduce through external fertilization.

Nucleotide content, oxidative phosphorylation, morphology, and fertilizing capacity of turbot (Psetta maxima) spermatozoa during the motility period

The interdependence between motility, respiration, ATP production, and utilization was investigated in intact spermatozoa of turbot (Psetta maxima), a marine teleost. When spermatozoa were diluted in a hyperosmotic medium (>300 mOsmol/kg), they immediately became motile, and the intracellular concentration of ATP as well as the adenylate energy charge ratio dropped concomitant with the straight-line velocity. The ADP and AMP levels increased from 1.4 to 8.0 nmole/10(8) cells and from 0.6 to 6.0 nmole/10(8) cells, respectively. Moreover, 31P-NMR spectra recorded prior to the swimming phase revealed the presence of phosphomonoesters (PMEs) and phosphodiesters (PDEs), intracellular inorganic phosphate (Pi), and phosphocreatine (PCr). At the end of the motility period, PCr, PDE, and PME decreased, while the Pi level increased markedly. Following initiation of motility, O2 consumption of spermatozoa increased from 34.9 to 124.8 O2 nmole/10(9) spermatozoa/min. FCCP, an uncoupler of oxidative phosphorylation, did not significantly affect the respiratory rate of motile spermatozoa. Ouabain, a specific inhibitor of (Na+/K+)/ATPase, slightly decreased the respiration rate of motile spermatozoa, indicating that the major part of ATP catabolism was linked to dynein ATPase. Inhibitors of the respiratory chain (KCN, NaN3, NaHCO3-, oligomycin) reduced sperm respiration, percentage of motile cells, velocity, and adenylate contents. Following the reactivation of motility of demembranated spermatozoa, KCN, NaN3, NaHCO3- altered the flagellar beat frequency, demonstrating that these respiratory inhibitors possess action sites other than mitochondria. Mitochondrial oxidative phosphorylation is highly requested to produce energy required during motion. Nevertheless it is insufficient to maintain endogenous ATP stores. A second phase of motility was induced by a transfer of exhausted spermatozoa into an ionic medium of low osmolality (200 mOsmol/kg) for 30 min. Spermatozoa, once reactivated in AM, recovered 55% of initial motility and 31% of initial fertilization rate. In hypo-osmotic medium, mitochondrial oxidative phosphorylation also induced ATP regeneration. Following activation of movement, several morphological changes were observed in the mitochondria and the midpiece.

Morphological and kinetic changes of carp (Cyprinus carpio) spermatozoa after initiation of motility in distilled water

Studies on the flagellar movement of carp spermatozoa induced by dilution in distilled water allowed us to describe a sequence of early, rapid morphological and kinetic changes which begin at the very tip of the flagellum. They cause the progressive folding of the axoneme which ends stuck to the head within 90-120 seconds after the initiation of motility. However, the axonemal machinery remains functional as the folding can be reversed after transfer back into a high osmolality medium and partially folded flagella were able to propagate efficient waves along the non-folded proximal portion of the axoneme. The data also revealed that the membrane area of the terminal piece exhibits strong sensitivity to hypotonicity. These results suggest that in the normal freshwater medium, the brief swimming period allowing fertilization of oocytes is limited by the osmotic stress induced coiling of the carp sperm tail and not by ATP stores.

Ultrastructural study of osmolality effect on spermatozoa of three marine teleosts

With particular emphasis on mitochondria that may provide endogenous energy for spermatozoan motility, the morphological changes of the spermatozoa of three marine teleosts, black porgy (Acanthopagrus schlegelli), black grouper (Epinephelus malabaricus), and Atlantic croaker (Micropogonias undulatus), were compared either after activation in artificial sea water or when immersed in various osmotic pressure media. The midpieces of these three teleosts spermatozoa are composed of mitochondria surrounding the flagellum. Each mitochondrion is enclosed by distinct outer and inner membranes. The inner membrane separates the organelle's volume into two phases: the matrix and the intermembrane space. The inner membrane displays numerous infolding cristae that vary in number and shape and extend into the matrix. Following activation with artificial sea water, spermatozoa became motile and both the size and number of mitochondria decrease and then totally disappear. The present study strongly suggests that an energy source(s), responsible for motility, is located within the mitochondria in the midpiece of these three marine teleost spermatozoa.

Relationship between sperm ATP content and motility of carp spermatozoa

Carp spermatozoa are immotile in seminal plasma or in saline solution of high osmolality (&gt; 400 mosmol kg-1). These ‘quiescent’ spermatozoa initiate a progressive forward motility when transferred in freshwater or in saline solution with low osmolality (&lt; 160 mosmol kg-1). In this study we investigated ‘in vitro’ the relationship between sperm ATP content (measured by bioluminescence) and sperm motility (analysed by videomicroscopy). Sperm ATP content remained high in the immobilizing medium (200 mM KCl, Tris 30 mM, pH 8.0) where no flagellar movement occurs. Dilution of these spermatozoa in the activating medium (45 mM NaCl, 5 mM KCl, Tris 30 mM, pH 8.0) triggered forward motility which varied with temperature. At 20 degrees C, sperm ATP content decreased rapidly during the progressive forward motility phase from 12 to 4 nmol/10(8) spermatozoa, concomitantly with decreases in velocity (130 to 10 microns s-1) and the beat frequency (50 to 7 Hz). An inhibitor of mitochondrial respiration (KCN 10 mM) produced a drop in sperm ATP content irrespective of the incubation medium (activating or immobilizing). A second phase of sperm motility in the activating medium was induced following a previous transfer of spermatozoa into a medium of high osmolality for a few minutes prior to the second phase. Within 10 minutes, spermatozoa recover 90% of the initial ATP level as well as forward motility. These results suggest that motility of carp spermatozoa depends on sperm ATP synthesized by mitochondrial respiration mainly stored before activation. In low osmolality conditions, the mitochondrial oxidative phosphorylation is unable to compensate for the ATP hydrolysis required to sustain motility.(ABSTRACT TRUNCATED AT 250 WORDS)