The effect of temperature on sperm motility and enzymatic activity in brown trout Salmo trutta, burbot Lota lota and grayling Thymallus thymallus

Hormone-Driven Temperature Optimization for Elevated Reproduction in Goldfish (Carassius auratus) under Laboratory Conditions

This study investigates the efficacy of hormone-induced artificial reproduction in goldfish (Carassius auratus) under controlled temperatures. Ovaprim injections significantly enhanced ovulation and sperm production compared to controls. Medium temperature (22 °C) produced the highest ovulation rates, fastest ovulation timing, and optimal sperm quality (motility and morphology) compared to high (28 °C) and low (16 °C) temperature groups. The low-temperature group exhibited reduced sperm motility duration and higher rates of sperm and larvae damage. The sperm volume of the high-temperature group was higher, but their post-injection survival rates were lower. Furthermore, the lowest spawning rate and low egg quality were noted in the high temperature. Cryopreservation using extender E4 (15% DMSO) exhibited superior post-thaw sperm motility and achieved higher fertilization rates. Fertilization rates, embryo development, and larval survival were all highest at the medium temperature. Larvae hatched from fresh sperm at medium temperature exhibited faster growth and fewer deformities. These findings suggest that hormone stimulation coupled with a medium temperature regimen is critical for successful artificial reproduction in goldfish. Cryopreservation with extender E4 holds promise for sperm banking; however, further optimization is necessary to improve fertilization success with thawed sperm. Future research could explore the influence of temperature on sperm physiology and refine cryopreservation protocols to enhance fertilization rates.

Change in the swimming pattern of Salmo salar spermatozoa caused by the high temperature of the sperm motility activation medium

Fish are ectotherms and many have an external reproductive mode. An environmental factor which triggers fish reproductive activity in fish is water temperature. However, climate change is causing increasingly frequent events in which the water temperature varies rapidly; as a result, both in hatchery and in natural conditions, fish sperm are exposed to varying environmental temperatures during their journey toward the egg. This study was based on two experiments: The first experiment was designed to determine how storage at 4 °C for four days affected the sperm functions of Atlantic salmon (Salmo salar) sperm collected by either abdominal massage (stripping/Pure) or testicular dissection (testicular macerate/Macerated). Further, computer-assisted semen analysis (CASA) was used to compare sperm velocity parameters (VCL, VSL, and VAP) and progressivity (STR, LIN, and WOB) after motility activation at different temperatures (8 and 16 °C) of sperm collected by both methods (Pure vs Macerated). The results show that spermatozoa from Macerated samples maintained a higher sperm function when stored at 4 °C for 4 days compared to Pure sperm samples. In the second experiment, CASA determined that all parameters for sperm velocity (VCL, VSL, and VAP) and progressivity (STR (50%/55%), LIN (25%-32%), and WOB (51%-57%) were affected by activation temperature (P < 0.05) and that the motility patterns after activation at 16 °C (P < 0.05), specifically the LIN or STR swimming trajectories of the sperm differed between the two groups. In conclusion, the sperm quality of testicular Macerate was superior to that of Pure sperm abdominal mass, based on the higher quality of various sperm functions during short-term storage. Moreover, there was a significant effect of the temperature of the activation medium on sperm speed and progressivity (motility pattern) in the collected samples of testicular macerate. The sensitivity of Salmo salar spermatozoa to elevated temperature varies markedly between collection methods (Pure and Macerated).

Pre-fertilization gamete thermal environment influences reproductive success, unmasking opposing sex-specific responses in Atlantic salmon (Salmo salar)

The environment gametes perform in just before fertilization is increasingly recognized to affect offspring fitness, yet the contributions of male and female gametes and their adaptive significance remain largely unexplored. Here, we investigated gametic thermal plasticity and its effects on hatching success and embryo performance in Atlantic salmon (Salmo salar). Eggs and sperm were incubated overnight at 2°C or 8°C, temperatures within the optimal thermal range of this species. Crosses between warm- and cold-incubated gametes were compared using a full-factorial design, with half of each clutch reared in cold temperatures and the other in warm temperatures. This allowed disentangling single-sex interaction effects when pre-fertilization temperature of gametes mismatched embryonic conditions. Pre-fertilization temperature influenced hatch timing and synchrony, and matching sperm and embryo temperatures resulted in earlier hatching. Warm incubation benefited eggs but harmed sperm, reducing the hatching success and, overall, gametic thermal plasticity did not enhance offspring fitness, indicating vulnerability to thermal changes. We highlight the sensitivity of male gametes to higher temperatures, and that gamete acclimation may not effectively buffer against deleterious effects of thermal fluctuations. From an applied angle, we propose the differential storage of male and female gametes as a tool to enhance sustainability within the hatcheries.

The impact of time and environmental factors on the mitochondrial vesicle and subsequent motility of amphibian sperm

For amphibian species that display external fertilization in an aquatic environment, hypoosmotic shock to sperm cells can quickly result in damage to cellular structure and function. This study sought to determine how fertilization media osmolality, temperature, and time impact the stability of the mitochondrial vesicle's association with the sperm head and thus motility and quality of forward progression. The presence of the mitochondrial vesicle and its relationship with sperm motility and quality of forward progression were analyzed in sperm samples from the Fowler's toad (Anaxyrus fowleri) (n = 10) when held for six hours under two temperatures and four osmolalities. Results indicated that the presence of the mitochondrial vesicle is needed for sperm motility over time (p < 0.001), where higher osmolalities (p < 0.001) and lower temperatures (p < 0.001) correlated with maintaining the vesicle attachment to the spermatozoa. The higher osmolality of spermic urine was the most important factor for maintaining higher quality of forward progressive motility (p < 0.01) of spermatozoa. Sperm samples held at 4 °C and 40 mOsm/kg had the longest half-life for motility (540 min) and quality of forward progression (276 min), whereas sperm held at 22 °C and 2.5 mOsm/kg had the shortest half-life for motility (7 min) and quality of forward progression (18 min). Special attention should be given to the osmolality and temperature of fertilization solutions, or breeding tank water, when developing cold storage protocols for toad sperm or reproducing animals to ensure the retention of the mitochondrial vesicle for maximum fertilization capability.

Multiscale oscillations of the annual course of temperature affect the spawning events of rudd (Scardinus erythrophthalmus)

Identifying climate impacts on ecosystems and their components requires observing time series of sufficient length to ensure adequate statistical power and reasonable coverage of the historical range of variability inherent in the system. The complexity of the hierarchy of climate effects reflected in temporal patterns in time series creates a need to be accurately modeled. The life cycle phenomena of living organisms, including fish spawning, have the character of one-time or time-limited events in time. An approach to finding the relationship between continuous components of time dynamics of environment properties and life cycle events of living organisms was proposed. This approach allowed us to evaluate the role of temperature patterns in the phenology of spawning rudd (Scardinus erythrophthalmus Linnaeus, 1758) in the Dnipro River basin water bodies. The atmospheric temperature time series may be decomposed into the following components: trend, annual cycle, episodic component, harmonic component, extreme events, and noise. Systematically low water temperatures at the beginning of the spawning period were observed in the Protoka River system and the Obukhov floodplain, and systematically elevated temperatures were recorded in the Dnipro River. The annual temperature dynamics was shown to be presented as a composition of oscillatory processes of different scale levels. The sinusoidal trend was previously extracted from the temperature series data. The average annual temperature, amplitude, and phase shift were calculated on the basis of the sinusoidal regression model. The residuals of the sinusoidal trend were processed by means of redundancy analysis with variables derived from symmetric distance-based Moran’s eigenvector maps as explanatory predictors. A set of 104 orthogonal dbMEM variables was extracted from the annual time series. These temporal variables were divided into the broad-, medium-, and fine-scale components. The parameters of temperature dynamics and biotope type are able to explain 51–72% of variability of spawning event. The time of spawning in water bodies corresponds to the time of spawning start: the earlier spawning starts, the earlier it ends. The duration of the spawning season is influenced by the patterns of different scale levels, as well as the amplitude and shift of phases. In this case, the duration of spawning in all water bodies does not differ. Spawning temperature depends on medium- and fine-scale temperature patterns, but does not depend on the characteristics of the sinusoidal annual trend. The annual temperature variation has been shown to be such that it can be decomposed into a sinusoidal trend, patterns of a multiscale nature, and a random fraction. Over the time range studied, the trend of increasing mean annual temperature was not statistically significant for spawning events. The sinusoidal trend explains 78.3–87.6% of the temperature variations and depends on the mean annual temperature, the amplitude of temperature variations during the year, and the earlier or later seasons of the year. Amplitude and phase shift play a role in describing spawning phenology. The residuals of the sinusoidal trend have been explained using dbMEM variables. This variation was decomposed into large-scale, medium-scale, and small-scale components. Winter and spring temperature fluctuations prior to spawning initiation had the greatest effect on spawning. Water temperature determines the lower possible limit for the start of spawning, but the actual start of spawning is determined by the preceding temperature dynamics. The results of the study have implications for understanding the dynamics of fish populations and assessing the influence of environmental conditions on the harmonization of the various components of ecosystems.

The Physiological and Evolutionary Ecology of Sperm Thermal Performance

Ongoing anthropogenic climate change has increased attention on the ecological and evolutionary consequences of thermal variation. Most research in this field has focused on the physiology and behavior of diploid whole organisms. The thermal performance of haploid gamete stages directly tied to reproductive success has received comparatively little attention, especially in the context of the evolutionary ecology of wild (i.e., not domesticated) organisms. Here, we review evidence for the effects of temperature on sperm phenotypes, emphasizing data from wild organisms whenever possible. We find that temperature effects on sperm are pervasive, and that above normal temperatures in particular are detrimental. That said, there is evidence that sperm traits can evolve adaptively in response to temperature change, and that adaptive phenotypic plasticity in sperm traits is also possible. We place results in the context of thermal performance curves, and encourage this framework to be used as a guide for experimental design to maximize ecological relevance as well as the comparability of results across studies. We also highlight gaps in our understanding of sperm thermal performance that require attention to more fully understand thermal adaptation and the consequences of global change.

Plate-Based Respirometry to Assess Thermal Sensitivity of Zebrafish Embryo Bioenergetics in situ

Oxygen consumption allows measuring the metabolic activity of organisms. Here, we adopted the multi-well plate-based respirometry of the extracellular flux analyzer (Seahorse XF96) to investigate the effect of temperature on the bioenergetics of zebrafish embryos (Danio rerio) in situ. We show that the removal of the embryonic chorion is beneficial for oxygen consumption rates (OCR) and penetration of various mitochondrial inhibitors, and confirm that sedation reduces the variability of OCR. At 48h post-fertilization, embryos (maintained at a routine temperature of 28°C) were exposed to different medium temperatures ranging from 18°C to 37°C for 20h prior OCR measurement. Measurement temperatures from 18°C to 45°C in the XF96 were achieved by lowering the room temperature and active in-built heating. At 18°C assay temperature, basal OCR was low due to decreased ATP-linked respiration, which was not limited by mitochondrial power, as seen in substantial spare respiratory capacity. Basal OCR of the embryos increased with assay temperature and were stable up to 37°C assay temperature, with pre-exposure of 37°C resulting in more thermo-resistant basal OCR measured at 41°C. Adverse effects of the mitochondrial inhibitor oligomycin were seen at 37°C and chemical uncouplers disrupted substrate oxidation gradually with increasing assay temperature. Proton leak respiration increased at assay temperatures above 28°C and compromised the efficiency of ATP production, calculated as coupling efficiency. Thus, temperature impacts mitochondrial respiration by reduced cellular ATP turnover at lower temperatures and by increased proton leak at higher temperatures. This conclusion is coherent with the assessment of heart rate, an independent indicator of systemic metabolic rate, which increased with exposure temperature, peaking at 28°C, and decreased at higher temperatures. Collectively, plate-based respirometry allows assessing distinct parts of mitochondrial energy transduction in zebrafish embryos and investigating the effect of temperature and temperature acclimation on mitochondrial bioenergetics in situ.

Bioenergetic Pathways in the Sperm of an Under-Ice Spawning Fish, Burbot (Lota lota): The Role of Mitochondrial Respiration in a Varying Thermal Environment

Regarding the sperm of cold-water fish, the contributions of different bioenergetic pathways, including mitochondrial respiration, to energy production at the spawning temperature and its adaptation at the maximum critical temperature (CTmax) are unclear. The roles of glycolysis, fatty acid oxidation, oxidative phosphorylation (OXPHOS) at 4 °C, and OXPHOS at 15 °C for energy production in burbot (Lota lota) spermatozoa were studied by motility and the oxygen consumption rate (OCR) (with and without pathway inhibitors and the OXPHOS uncoupler). At both temperatures, the effects of the inhibitors and the uncoupler on the motility duration, curvilinear velocity, and track linearity were insignificant; in addition, the OCRs in activation and non-activation media differed insignificantly and were not enhanced after uncoupler treatment. After inhibitor treatment in both media, OXPHOS was insignificantly different at the 2, 30, and 60 s time points at 4 °C but was reduced significantly at the 30 and 60 s time points after treatment with sodium azide at 15 °C. In conclusion, for burbot sperm at both the spawning temperature and the CTmax, the energy synthesized via OXPHOS during motility was insufficient. Therefore, the majority of the energy required to sustain motility was derived from pre-accumulated energy produced and stored during the quiescent state of the spermatozoa.

Short-term storage of tiger salamander (Ambystoma tigrinum) spermatozoa: The effect of collection type, temperature and time

The aims of this project were to characterize tiger salamander (Ambystoma tigrinum) spermatozoa motility over time, when excreted as either milt or spermic urine prior to packaging into a spermatophore, and to determine the effect of temperature on sperm motility. A split-plot design was utilized to assess the motility of the two pre-spermatophore sample types at two temperatures, 0°C and 20°C (n = 10 for each treatment). Spermiation was induced through exogenous hormone treatment of luteinizing hormone releasing hormone analog in order to collect both milt and spermic urine, which were evaluated for motility, divided into two separate aliquots, and subsequently stored in either an ice-bath (0°C) or on the benchtop (20°C). The decay rate of sperm motility was assessed by reevaluating subsamples at 0.5, 1, 2, 3, 5, 7, and 24 hours following the initial assessment. Results showed that sperm stored at 0°C had significantly higher progressive, non-progressive, and total motility for both sperm collection types over time. An interaction was found between collection type and time, with milt exhibiting lower initial motility that was more sustainable over time, compared to spermic urine. For both milt and spermic urine, motility decreased rapidly with storage duration, indicating samples should be used as soon as possible to maximize motility for in-vitro fertilization and cryopreservation. This is the first study to describe the differences in sperm motility between milt and spermic urine from an internally fertilizing caudate and demonstrates the benefits of near freezing temperatures on sperm longevity.

Cryoprotective activity of phosphorus-containing phenol

The antioxidant and cryoprotective efficiencies of a 3,5-di-tert-butyl-4-hydroxyphenyl)methylenediphosphonic acid (MDPA) differ significantly for sperm cells of various species of sturgeon fish (Russian sturgeon, beluga and Stellate sturgeon). The ability of phosphorus-containing phenol MDPA to decrease the level of lipid peroxidation of sperm, beneficial effect on the activity indicators of the sperm of native sturgeon and of the defrosted one after deep freezing as well as on the fertility of sperm cells was shown.

Energy pathways associated with sustained spermatozoon motility in the endangered Siberian sturgeon Acipenser baerii

Sturgeon spermatozoa are unique for their sustained motility. We investigated the relative importance of bioenergetic pathways in the energy supply of Siberian sturgeon Acipenser baerii spermatozoa during motile and immotile states. Spermatozoon motility and oxygen consumption rate (OCR) were analysed following exposure to inhibitors of oxidative phosphorylation (sodium azide, NaN₃ ), glycolysis (2-deoxy-D-glucose, DOG) and β-oxidation of fatty acids (sodium fluoride, NaF), and to an uncoupler of oxidative phosphorylation (carbonyl cyanide m-chlorophenyl hydrazine, CCCP). No significant difference in curvilinear velocity was observed after addition of these reagents to activation medium (AM) or nonactivation medium (NAM) for incubation. Incubation of spermatozoa in NAM containing CCCP or NaN₃ resulted in significantly decreased motility duration compared to controls. The OCR of sturgeon spermatozoa in AM (11.9 ± 1.4 nmol O₂ min^-1 (10⁹  spz)^-1 ) was significantly higher than in NAM (8.2 ± 1.5 nmol O₂ min^-1 (10⁹  spz)^-1 ). The OCR significantly declined with addition of NaN₃ to AM and NAM. No significant difference in motility parameters or OCR was observed with NaF or DOG. These results suggest active oxidative phosphorylation in both immotile and motile spermatozoa. Nevertheless, mitochondrial respiration occurring during motility is not sufficient to meet the high energy demands, and the energy required for sustained motility of Siberian sturgeon spermatozoa is derived from adenosine triphosphate accumulated during the quiescent state.

In vitro antioxidant enzyme activity and sperm motility at different temperatures in sterlet Acipenser ruthenus and rainbow trout Oncorhynchus mykiss

Influence of in vitro temperature on sperm antioxidant enzyme activity, thiobarbituric acid-reactive substance (TBARS) content and motility parameters was evaluated in sterlet Acipenser ruthenus and rainbow trout Oncorhynchus mykiss. Sperm activation was conducted at 4, 14 and 24 °C in both species. Duration of motility was significantly longer at 4 °C than at 14 and 24 °C in both species. At 60 s post-activation, the velocity of sterlet spermatozoa was highest at 24 °C. This trend continued to 420 s post-activation. In rainbow trout, at 10 s post-activation, the highest velocity was observed at 14 °C. Significantly higher catalase activity was seen at 4 °C in both species. No significant difference in spermatozoon superoxide dismutase activity among temperatures was observed. In sterlet, TBARS content was significantly higher at 24 °C compared to other temperatures, but, in rainbow trout, it was highest at 4 °C. The results presume species-specific level of antioxidant enzyme activity and TBARS content at studied temperatures.

Effects of temperature on sperm motility of burbot Lota lota: spontaneous activation and calcium dependency

Several factors regulating activation of spermatozoon motility in Eurasian burbot, Lota lota, including osmolality, calcium (Ca²⁺ ) ions, and temperature were investigated. Spermatozoon motility in Eurasian burbot, Lota lota was assessed at 4 and 30°C in seminal fluid, isotonic media (with and without Ca²⁺ ) and hypotonic media (with and without Ca²⁺ ). Spermatozoa were spontaneously activated in seminal fluid at 20°C and the maximum motility was recorded at 30°C, which is out of the spawning temperature range, indicating that no risk of activation occurs during routine semen handling in artificial insemination. Initiation of spermatozoon motility in L. lota is mediated by Ca²⁺ and sensitivity to Ca²⁺ is dependent on temperature.

Formation of an antioxidant profile in the sea trout (Salmo trutta m. trutta L.) from the Slupia River

Using a stage- and sex-based multivariate significance tests on the sea trout Salmo trutta m. trutta L. model, we show dependencies in the balance between lipid peroxidation processes, levels of carbonyl derivatives, and activity of antioxidant enzymes (superoxide dismutase SOD, catalase CAT, glutathione reductase GR, and peroxidase GPx) in the processes of antioxidant profile formation during the fish growing process. The study was aimed at examination of the relationships between the biomarkers of oxidative stress estimated by the total antioxidant status as well as the dependencies between the sex (male, female) and developmental stage of the wild sea trout from the Slupia River and its catchment area rivers. Functioning of the pro/antioxidant balance of the liver tissue reflected the course of the individual developmental stages of the trout and was associated with significant intensification of lipoperoxidation, oxidative modification of proteins, and reduction of the total antioxidant capacity of fish along with age. Formation of a holistic model for the analysis of the involvement of all parameters of antioxidant protection in all stages of development and sex allowed us to obtain the following rank order for the level of lipoperoxidation processes, modified proteins, and antioxidant enzyme complex: CAT > SOD > GPx > GR and TBARS > OMP KD > TAC > OMP AD.

Swimming at different temperatures: The lipid composition of sperm from three freshwater fish species determined by mass spectrometry and nuclear magnetic resonance spectroscopy

The spawning behavior of different fish species is as diverse as their habitats. A lot of factors influence the (phospho)lipid composition of fish sperm, including the water temperature at which spawning takes place. Therefore, this study aimed on the elucidation of the phospholipid composition of sperm from three fish species from different orders (common carp - Cyprinus carpio, northern pike - Esox lucius and burbot - Lota lota) with different spawning temperatures by nuclear magnetic resonance spectroscopy (NMR), matrix-assisted laser desorption/ionization mass spectrometry and thin-layer chromatography (TLC) coupled to electrospray ionization mass spectrometry as well as gas chromatography. Next to the lipid composition that was different for carp, northern pike and burbot, regarding the moieties of the different (phospho)lipid classes (particularly sphingomyelin and acidic phospholipids) and the saturation degree of the fatty acyl residues, there were differences observed depending on the analytical method that was used. The results from TLC and NMR investigations differed regarding the amounts of the different phospholipids. Reasons for these discrepancies are discussed in detail.

Sperm motility of the Nile tilapia (Oreochromis niloticus): Effects of temperature on the swimming characteristics

Results of previous studies with different fish species, mostly from temperate- or cold-water habitats, indicate a species-specific diversity regarding the relationship between environmental temperature and values for sperm motility variables. In the current study, there was appraisal of environmental temperature effects on sperm motility of tilapia Oreochromis niloticus, a tropical fish species selected because of its aquaculture importance and capacity to reproduce in a broad range of water temperatures. Effects of environmental temperature on the spermatozoa motility characteristics were studied by temperature-controlled video-microscopy and CASA analysis at temperature range from 5 to 50 °C. It appeared that the Nile tilapia spermatozoa exhibit an unexpected capacity to express very different velocity characteristics over this temperature range. In the lower temperature range (5-10 °C), the percentage of motile cells was markedly variable among males. An abrupt increase in the linearity index was observed between 15 and 20 °C suggesting a physiological threshold in sperm movement at about 20 °C which is the minimum temperature for reproduction in the Nile tilapia. With faster spermatozoa velocity, there was a reduction of the motility duration at the greater temperatures. Initially, there is an increase in sperm velocity as the temperature increased until the maximal velocity occurred at 40 to 50 °C which is a temperature beyond that which occurs in natural spawning conditions. Results of the present study clearly indicate the importance of considering ambient temperature when charactering sperm motility and in determining optimal temperature conditions for fertilization in fish.

Sperm pre-fertilization thermal environment shapes offspring phenotype and performance

The sperm pre-fertilization environment has recently been suggested to mediate remarkable transgenerational consequences for offspring phenotype (transgenerational plasticity, TGB), but the adaptive significance of the process has remained unclear. Here, we studied the transgenerational effects of sperm pre-fertilization thermal environment in a cold-adapted salmonid, the European whitefish (Coregonus lavaretus). We used a full-factorial breeding design where the eggs of five females were fertilized with the milt of 10 males that had been pre-incubated at two different temperatures (3.5°C and 6.5°C) for 15 h prior to fertilization. Thermal manipulation did not affect sperm motility, cell size, fertilization success or embryo mortality. However, offspring that were fertilized with 6.5°C-exposed milt were smaller and had poorer swimming performance than their full-siblings that had been fertilized with the 3.5°C-exposed milt. Furthermore, the effect of milt treatment on embryo mortality varied among different females (treatment×female interaction) and male-female combinations (treatment×female×male interaction). Together, these results indicate that sperm pre-fertilization thermal environment shapes offspring phenotype and post-hatching performance and modifies both the magnitude of female (dam) effects and the compatibility of the gametes. Generally, our results suggest that short-term changes in sperm thermal conditions may have negative impact for offspring fitness. Thus, sperm thermal environment may have an important role in determining the adaptation potential of organisms to climate change. Detailed mechanism(s) behind our findings require further attention.

Spermatozoa quality and sperm lipid composition in intensively cultured and wild burbot (Lota lota)

The aim of this study was to compare the spermatozoa quality parameters in spermatozoa of RAS (Recirculating Aquaculture System; RAS group) cultured (commercial pellets) and natural condition cultured (WILD group) burbot Lota lota (live prey, Pseudorasbora parva). Seven of nine fish of the RAS group produced sperm, with sperm from only four of the fish having a motility of >5%. Sperm were collected from all nine fish of the WILD group, and sperm of six of the fish from the WILD group had motility of about 100% and three had sperm with 50% to 60% motility. Spermatozoa from the RAS group had a delay in activation compared to the WILD group. Fish from the RAS group also had a lesser volume of sperm (1.8 ± 1.2 mL) collected compared to the WILD group (3.6 ± 1.2 mL). Compared to the RAS group, sperm of the WILD group had a greater proportion of saturated fatty acids (SFA), as well as the phospholipid, phosphatidylethanolamine. The findings indicate that fish grown in natural conditions may be more suitable as broodstock. Ongoing research to develop methods of enhancing reproductive performance of burbot broodstock cultured in RAS is needed to investigate whether the quality of sperm can be improved by adjusting environmental conditions, diet, or combination of these factors.

Sperm in hot water: direct and indirect thermal challenges interact to impact on brown trout sperm quality

Climate change alters the thermal habitat of aquatic species on a global scale, generating novel environmental challenges during all life stages, including reproduction. Changes in water temperature profoundly influence the performance of ectothermic aquatic organisms. This is an especially crucial issue for migratory fish, because they traverse multiple environments in order to reproduce. In externally fertilizing migratory fish, gametes are affected by water temperature indirectly, within the reproductive organ in which they are produced during migration, as well as directly, upon release into the surrounding medium at the spawning grounds. Both direct (after release) and indirect (during production) thermal impacts on gamete quality have been investigated, but never in conjunction. Here, we assessed the cumulative influence of temperature on brown trout, Salmo trutta, sperm quality during sperm production (male acclimation temperature) as well as upon release (sperm activation water temperature) on two consecutive dates during the brown trout spawning season. Early in the season, warm acclimation of males reduced their fertilization probability (lower sperm velocity) when compared with cold-acclimated males, especially when the activation water temperature was also increased beyond the thermal optimum (resulting in a lower proportion of motile sperm with lower velocity). Later in the season, sperm quality was unaffected by acclimation temperature and thermal sensitivity of sperm was reduced. These results give novel insights into the complex impacts of climate change on fish sperm, with implications for the reproduction and management of hatchery and wild trout populations in future climate scenarios.

Effects of storage time on the motility, mortality and calcium levels of Atlantic salmon Salmo salar spermatozoa

This study estimates spermatozoa mortality, morphology, motility and intracellular calcium levels in Atlantic salmon Salmo salar milt after prolonged storage. Milt samples were preserved at 4° C for 25 days and then evaluated for mortality. Motility remained high for the first 3 days and the mortality was low during the first 5 days of storage. A decrease of >50% in calcium content was observed after 5 days of storage. When spermatozoa were activated, calcium levels increased >200% in relative fluorescence units (RFU); this rate of increase was lost when the samples were stored for extended periods of time and was only partially manifested in a zero calcium solution. The results suggest that in vitro storage of S. salar spermatozoa at 4° C for a period of 3 days preserves motility and limits mortality to levels similar to those of fresh spermatozoa. This method also maintains intracellular calcium storage critical for spermatozoa performance.

Analysis of common carp Cyprinus carpio sperm motility and lipid composition using different in vitro temperatures

In fish, sperm quality is frequently associated with sperm motility variables. The response of sperm motility to different temperatures varies among species and plasma membrane lipid composition may contribute to variations in findings in previous research. In the present study, sperm motility and lipid composition were analysed between motile or immotile carp Cyprinus carpio sperm at different in vitro temperatures (4, 14 and 24°C). The duration of the period over which sperm motility is sustained was longer at 4°C compared with 14 and 24°C; while sperm velocity was greatest at 24°C. Motile sperm had lesser proportions of 18:3 (n-3) and 22:6 (n-3) fatty acids at 24°C relative to immotile sperm. There was no difference in fatty acid composition of motile and immotile sperm at 4 and 14°C. The total phospholipid content was less in motile than in immotile sperm at 24°C. At 24°C, phosphatidylcholine and phosphatidylserine proportions were less in motile than immotile sperm. It is concluded that lipid composition of motile carp sperm is affected by temperature, with greater temperatures associated with reduced lipid content, elevation of sperm curvilinear velocity and a decreased duration of the period over which motility is sustained.

Temporal plasticity in thermal-habitat selection of burbot Lota lota a diel-migrating winter-specialist

In this study, animal-borne telemetry with temperature sensors was coupled with extensive habitat temperature monitoring in a dimictic reservoir, to test the following hypotheses: behavioural thermoregulation occurs throughout the year and temperature selection varies on a diel and seasonal basis, in a winter-specialist diel-migrating fish. Burbot Lota lota demonstrated nightly behavioural thermoregulation throughout the year, with a large seasonal shift between selection for very cold temperatures (<2° C) optimal for reproduction during the spawning period and selection for warmer temperatures (12-14° C) optimal for hunting and feeding during non-reproductive periods. During daylight hours, while L. lota avoided habitats warmer than optimal for reproduction and feeding during the spawning and non-reproductive periods, respectively, active selection was limited to selection for 4-6° C habitat during the prespawning period. Although behavioural thermoregulation explained the night-time migration, behavioural thermoregulation only partially explained daytime behaviour, indicating that diel migration is best explained by a combination of factors. Thus, thermal-habitat selection was a good predictor of night-time habitat occupancy in a diel-migrating species. Together, these results show that thermal-habitat selection by fishes may be important throughout the year and a more seasonally plastic behaviour than previously recognized.

Enzyme activity in energy supply of spermatozoon motility in two taxonomically distant fish species (sterlet Acipenser ruthenus, Acipenseriformes and common carp Cyprinus carpio, Cypriniformes)

As spermatozoon motility duration differs significantly among fish species, the mechanism of ATP generation-regeneration and its distribution along the flagellum may be species-dependent. The present study compared the role of creatine kinase (CK) with that of adenylate kinase (AK) in ATP regeneration during motility of demembranated spermatozoa of taxonomically distant fish species, sterlet, and common carp, allowing investigation for the presence of the creatine-phosphocreatine (PCr) shuttle in sterlet spermatozoa. The flagellar beat frequency of demembranated spermatozoa was measured in reactivating media in the presence or absence of ATP, ADP, PCr, and CK and AK inhibitors. After demembranation, AK, CK, and total ATPase activity was measured in spermatozoon extracts. Beat frequency of demembranated spermatozoa was found to be positively correlated with ATP levels in reactivating medium and to reach a plateau at 0.8 mM and 0.6 mM ATP for carp and sterlet, respectively. It was shown for the first time that sterlet axonemal dynein ATPases have a higher affinity for ATP than do those of carp. Supplementation of reactivating medium with ADP and PCr without ATP resulted in beat frequencies comparable to that measured with 0.3 to 0.5-mM ATP for both studied species. The presence of the PCr-CK phosphagen system and its essential role in ATP regeneration were first confirmed for sturgeon spermatozoa. The inhibition of CK exerted a high impact on spermatozoon energy supply in both species, whereas the inhibition of AK was more pronounced in sterlet than in carp. This was confirmed by the quantification of enzyme activity in spermatozoon extracts. We concluded that spermatozoa of these taxonomically distant species use similar systems to supply energy for flagella motility, but with different efficacy.

Thermosensitive ion channel TRPV1 is endogenously expressed in the sperm of a fresh water teleost fish (Labeo rohita) and regulates sperm motility

Sperm cells exhibit extremely high sensitivity in response to slight changes in temperature, osmotic pressure and/or presence of various chemical stimuli. In most cases throughout the evolution, these physico-chemical stimuli trigger Ca (2+)-signaling and subsequently alter structure, cellular function, motility and survival of the sperm cells. Few reports have recently demonstrated the presence of Transient Receptor Potential (TRP) channels in the sperm cells from higher eukaryotes, mainly from higher mammals. In this work, we have explored if the sperm cells from lower vertebrates can also have thermo-sensitive TRP channels. In this paper, we demonstrate the endogenous presence of one specific thermo-sensitive ion channel, namely Transient Receptor Potential Vanilloid family member sub type 1 (TRPV1) in the sperm cells collected from fresh water teleost fish, Labeo rohita. By using western blot analysis, fluorescence assisted cell sorting (FACS) and confocal microscopy; we confirm the presence of this non-selective cation channel. Activation of TRPV1 by an endogenous activator NADA significantly increases the quality as well as the duration of fish sperm movement. The sperm cell specific expression of TRPV1 matches well with our in silico sequence analysis. The results demonstrate that TRPV1 gene is conserved in various fishes, ranging from 1-3 in copy number, and it originated by fish-specific duplication events within the last 320 million years (MY). To the best of our knowledge, this is the first report demonstrating the presence of any thermo-sensitive TRP channels in the sperm cells of early vertebrates as well as of aquatic animals, which undergo external fertilization in fresh water. This observation may have implications in the aquaculture, breeding of several fresh water and marine fish species and cryopreservation of fish sperms.

The effects of elevated temperature on the sexual traits, immunology and survivorship of a tropical ectotherm

In 2007, the Intergovernmental Panel on Climate Change projected an average global air temperature increase of 1.1-6.4°C by the end of the 21st century. Although the tropics are predicted to experience less extreme temperature increases than regions of higher latitude, tropical ectotherms live close to their thermal limits, and are thus particularly vulnerable to increases in temperature. In this study, we examined how predicted patterns of global warming will affect survival and sexual traits in the Trinidadian guppy (Poecilia reticulata). Guppies were exposed from birth to one of four temperature treatments: 23, 25 (control), 28 or 30°C. We measured brood survival and, at sexual maturity, male ornamentation, sperm traits and immune response. Our results show that increases in temperature result in guppies that have shorter, slower sperm but that there is an optimum temperature for ornamental hue at 28°C. Given the importance of sperm quality for reproduction, these results suggest population viability could be affected by warming. However, we found no difference in brood survival or immune response to a novel antigen across the treatments, indicating that survival may not be as vulnerable as previously thought. Overall, our data suggest that male sexual traits, and in particular sperm performance, are more sensitive than survival to a warming environment.