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The aim of this experiment was to assess the effect of media viscosity on ram sperm motility, kinematics and rheotaxis in vitro by using methylcellulose as a media thickener. Frozen–thawed semen of three rams was thawed and diluted in Tyrode's albumin lactate pyruvate (TALP) media supplemented with 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6% and 0.7% w/v of methylcellulose. Sperm motility and kinematic characteristics were analysed using computer‐assisted sperm analysis (CASA). The rheotactic behaviour was assessed in a microfluidic channel, and the number of spermatozoa that passed the 10 mm point of a microfluidic channel over a 2min period against a flow rate of 30 μm/sec was assessed. The use of media with higher viscosity (higher levels of methylcellulose) resulted in significantly lower (p <.05) sperm motility and kinematic parameters. Moreover, higher levels of methylcellulose reduced (p <.05) the number of spermatozoa that exhibited positive rheotaxis. In conclusion, viscosity affected the kinematic properties and rheotactic behaviour of ram sperm. [ABSTRACT FROM AUTHOR]

Background: Obtaining functional sperm cells is the first step to treat infertility. With the ever‐increasing trend in male infertility, clinicians require access to effective solutions that are able to single out the most viable spermatozoa, which would max out the chance for a successful pregnancy. The new generation techniques for sperm selection involve microfluidics, which offers laminar flow and low Reynolds number within the platforms can provide unprecedented opportunities for sperm selection. Previous studies showed that microfluidic platforms can provide a novel approach to this challenge and since then researchers across the globe have attacked this problem from multiple angles. Objective: In this review, we seek to provide a much‐needed bridge between the technical and medical aspects of microfluidic sperm selection. Here, we provide an up‐to‐date list on microfluidic sperm selection procedures and its application in assisted reproductive technology laboratories. Search method: A literature search was performed in Web of Science, PubMed, and Scopus to select papers reporting microfluidic sperm selection using the keywords: microfluidic sperm selection, self‐motility, non‐motile sperm selection, boundary following, rheotaxis, chemotaxis, and thermotaxis. Papers published before March 31, 2023 were selected. Outcomes: Our results show that most studies have used motility‐based properties for sperm selection. However, microfluidic platforms are ripe for making use of other properties such as chemotaxis and especially rheotaxis. We have identified that low throughput is one of the major hurdles to current microfluidic sperm selection chips, which can be solved via parallelization. Conclusion: Future work needs to be performed on numerical simulation of the microfluidics chip prior to fabrication as well as relevant clinical assessment after the selection procedure. This would require a close collaboration and understanding among engineers, biologists, and medical professionals. It is interesting that in spite of two decades of microfluidics sperm selection, numerical simulation and clinical studies are lagging behind. It is expected that microfluidic sperm selection platforms will play a major role in the development of fully integrated start‐to‐finish assisted reproductive technology systems. [ABSTRACT FROM AUTHOR]

Several factors influence whether an organism remains in its local habitat. Parasites can, for example, influence host movement by impacting their behavior, physiology, and morphology. In rivers, fish that swim efficiently against the current are able to maintain their position without being displaced downstream, a behavior referred to as positive rheotaxis. We hypothesized that both the presence and number of ectoparasites on a host would affect the ability of fish to avoid downstream displacement and thus prevent them from remaining in their habitat. We used the guppy‐Gyrodactylus host‐ectoparasite model to test whether parasite presence and parasite load had an effect on fish rheotaxis. We quantified rheotaxis of sham‐infected and parasite‐infected fish in a circular flow tank in the laboratory prior to infection and 5–6 days postinfection. Both parasite‐infected and sham‐infected individuals expressed similar levels of positive rheotaxis prior to infection and after infection. However, with increasing parasite numbers, guppies covered less distance in the upstream direction and spent more time in slower flow zones. These results suggest that higher numbers of Gyrodactylus ectoparasites negatively influence rheotactic movements. Further research is needed to understand the ecological and evolutionary implications of this ectoparasite on fish movement. [ABSTRACT FROM AUTHOR]

Throughout the world, louver‐bypass systems are a common method for fish protection at water diversion sites. Their performance has been evaluated for pelagic, strong‐swimming teleost fishes, but limited information exists regarding the effectiveness of louvers for guiding sturgeon, despite being a globally threatened taxon. This study used controlled laboratory experiments to quantify louver efficiency for juvenile green sturgeon under a range of conditions. Fish guidance efficiency was influenced most strongly by fish size and approach velocity, with poor efficiency for small fish at high velocities. Low velocities and, to a lesser extent, daylight conditions allowed a greater proportion of fish to remain upstream of the louver at all sizes. High velocities resulted in the greatest contact rate between the sturgeon and louver face. Louvers can be effective for benthic, weak‐swimming fish, but site‐ and species‐specific needs should always be considered in the development or operation of a louver guidance system. [ABSTRACT FROM AUTHOR]

Herein, the microfluidic device technique was used to investigate the effects of GDF‐9 concentrations and exposure time on the ram sperm positive rheotaxis (PR). Semen was collected from six rams and utilized for PR, motility and sperm kinetic parameter analysis using a computer‐assisted sperm analysis program with controlled flow velocity following 0, 10, 20 or 30 min of incubation at 37°C with GDF‐9 (200 , 400 or 600 ng/ml; semen sample without GDF‐9 was used as a control). Results revealed that there was not an interaction between effects of GDF‐9 concentrations and incubation duration on PR% (p =.457) and TM% (p =.099). A simple main effects analysis showed that GDF‐9 concentrations had an effect on PR% (p =.003). However, the incubation duration did not have an effect on PR% (p =.101). GDF‐9 concentrations had not an effect on TM% (p =.817). By contrast, the incubation duration affected on TM% (p =.026). A higher PR% was found (p <.05) at 200 ng GDF‐9 after 10 min (46.7 ± 10.3) and 20 min (45.5 ± 11.5) of incubation. After 30 min of incubation, the PR% was found lowest (p <.05) at 400 ng of GDF‐9 (30.6 ± 14.1) and 600 ng of GDF‐9 (32.2 ± 9.6). There was no difference (p >.05) in the sperm kinetic parameters between the four treatment groups. In conclusion, the ram sperms had the best rheotaxis properties after 10 and 20 min of incubation with 200 ng of GDF‐9 and were sensitive to high concretions. [ABSTRACT FROM AUTHOR]

Animals may signal behavioural responses to climate stressors. To date, there has been no study investigating the altered behaviour of birds due to the synergetic effects of wind, solar radiation and ambient temperature in natural environments. We analysed the body orientation of three close‐related Charadriiformes species with different body masses in response to wind speed, wind direction, sun position and ambient temperature on beaches in south‐eastern Brazil. We expected these birds to adjust their postures according to the intensity of climate stressors and their different body masses. We found that regardless of body mass, resting birds faced the wind according to its speed and reduced their surface area exposed to airflow. They also exhibited a perpendicular orientation to the sun in lower ambient temperatures, which correlated with higher wind speeds. The behavioural adjustments of resting birds to concomitant climate stressors may prevent body destabilization and promote thermoregulation and energy savings. [ABSTRACT FROM AUTHOR]

Social context may influence the perception of sensory cues and the ability to display refined behavioral responses. Previous work suggests that effective responses to environmental cues can be contingent on having a sufficient number of individuals in a group. Thus, the changes in group size may have profound impacts, particularly on the behavior of small social groups. Using zebrafish (Danio rerio), here we examined how changes in group size influence the ability to respond to changes in water flow. We found that fish in relatively larger groups displayed stronger rheotaxis even when comparing pairs of fish with groups of four fish, indicating that a small increase in group size can enhance the responsiveness to environmental change. Individual fish in relatively larger groups also spent less time in the energetically costly leading position than individuals in pairs, indicating that even a small increase in group size may provide energetic benefits. We also found that the shoal cohesion was dependent on the size of the group but within a given group size, shoal cohesion did not vary with the flow rate. Our study highlights that even a small change in group size could significantly affect the way social fish respond to the changes in water flow, which could be an important attribute that shapes the resilience of social animals in changing environments. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the effect of kisspeptin‐10 (Kp10) injection on semen characteristics, testosterone (T) production and sperm rheotaxis using microfluidic devices in immature ram. Computer‐assisted sperm analysis (CASA) with controlled flow velocity was used to explore the kinetic parameters of sperm and positive rheotaxis (PR %). PR % was defined as the number of PR sperms over the number of motile sperms. Healthy Ossimi rams were randomly divided into two groups; a saline‐treated control group and Kp10‐treated one (5 µg/kg body weight). Treatments were given by intramuscular injection once a week for 1 month. After 1 month, the semen was collected and evaluated weekly for 6 weeks, while the blood samples were collected every 2 weeks for the next 8 weeks. Semen properties were significantly affected by Kp10 injection (p <.01). The Kp10 increased the volume, sperm concentration and percentages of live sperm compared with those of control. Additionally, sperm trajectories and rheotaxis get improved by the injection of Kp10 with time. Furthermore, kisspeptin improved the secretion of testosterone levels throughout the period of study. In conclusion, injections of the Kp10 had a positive impact on semen characteristics as well as improved sperm rheotaxis of Ossimi rams in subtropics. [ABSTRACT FROM AUTHOR]

Immunity is a central component of fitness in wild animals, but its determinants are poorly understood. In particular, the importance of locomotory activity as a constraint on immunity is unresolved. Using a piscine model (Gasterosteus aculeatus), we combined a 25‐month observational time series for a wild lotic habitat with an open flume experiment to determine the influence of locomotor activity (countercurrent swimming) on natural variation in immune function. To maximize the detectability of effects in our flume experiment, we set flow velocity and duration (10 cm/s for 48 hr) just below the point at which exhaustion would ensue. Following this treatment, we measured expression in a set of immune‐associated genes and infectious disease resistance through a standard challenge with an ecologically relevant monogenean infection (Gyrodactylus gasterostei). In the wild, there was a strong association of water flow with the expression of immune‐associated genes, but this association became modest and more complex when adjusted for thermal effects. Our flume experiment, although statistically well‐powered and based on a scenario near the limits of swimming performance in stickleback, detected no countercurrent swimming effect on immune‐associated gene expression or infection resistance. The field association between flow rate and immune expression could thus be due to an indirect effect, and we tentatively advance hypotheses to explain this. This study clarifies the drivers of immune investment in wild vertebrates; although locomotor activity, within the normal natural range, may not directly influence immunocompetence, it may still correlate with other variables that do. [ABSTRACT FROM AUTHOR]

Contents The aim of the present research is to study the effect of pH values on the sperm rheotaxis properties. Semen collected from bulls was diluted with SOF medium (1:10). pH of the medium was adjusted using a digital pH meter to the following pH values: 6.0, 6.2, 6.4, 6.4, 6.8, 7.0. All kinetic parameters of sperm ( n = 3,385) were determined through a computer-assisted sperm analysis ( CASA) system using microfluidic devices with controlled flow velocity. The following parameters were determined: total motility ( TM%), positive rheotaxis ( PR%), straightline velocity ( VSL, μm/s), average path velocity ( VAP, μm/s), linearity ( LIN, as VSL/ VCL, %), beat cross-frequency ( BCF, Hz) and curvilinear velocity ( VCL, μm/s). Nitric oxide, calcium and potassium were estimated in semen at different pH values. To confirm the effect of nitric oxide and K+, we used sodium nitroprusside (an NO donor) and KCL as (a K+ donor) to see their effect on sperm PR%. The results showed no difference in TM% at pH (6-7). The PR% was the lowest at pH 6 and 7. The best parameters for the PR% were at pH 6.4-6.6. The concentration of Ca+2 did not change at different pH values. The mean NO values decreased with the increase of pH; however, the mean values of K+ increased with the increase of pH. Addition of high concentration of NO and K+ to the semen media at fixed pH level had a negative effect on TM% and PR%. In conclusion, the bull sperm had the best rheotaxis properties at pH 6.4-6.6 and sensitive to the change of seminal NO and K+. [ABSTRACT FROM AUTHOR]

Environmental cues that are associated with individual movement of threatened Gulf Sturgeon from upriver areas to nearshore and offshore winter feeding areas have been described throughout much of their range in the Gulf of Mexico. In this study, we focus on small-scale movement of Gulf Sturgeon between summer 'holding' areas and the fall staging area in the Pascagoula River system (Mississippi, USA). We evaluated a set of logistic regression models using Akaike's Information Criterion and found that relative changes in barometric pressure, time of day, and water temperature were cues for small-scale Gulf Sturgeon movements during fall outmigration. Numerous environmental cues appear to drive the activity of Gulf Sturgeon in staging areas, indicating the complexity of abiotic factors affecting the observed staging patterns during emigration. The identification of the environmental drivers that are associated with Gulf Sturgeon movement is particularly important if these known saline transition zones change spatially annually with variable rainfall or due to water withdrawals and are used by Gulf Sturgeon making osmotic adjustments while moving downriver. [ABSTRACT FROM AUTHOR]

To assess how flow affects school structure and threat detection, startle response rates of solitary and small groups of giant danio Devario aequipinnatus to visual looming stimuli were compared in flow and no-flow conditions. The instantaneous position and heading of each D. aequipinnatus was extracted from high-speed videos. Behavioural results indicate that (1) school structure is altered in flow such that D. aequipinnatus orient upstream while spanning out in a crosswise direction, (2) the probability of at least one D. aequipinnatus detecting the visual looming stimulus is higher in flow than no flow for both solitary D. aequipinnatus and groups of eight D. aequipinnatus; however, (3) the probability of three or more individuals responding is higher in no flow than in flow. These results indicate a higher probability of stimulus detection in flow but a higher probability of internal transmission of information in no flow. Finally, results were well predicted by a computational model of collective fright response that included the probability of direct detection (based on signal detection theory) and indirect detection ( i.e. via interactions between group members) of threatening stimuli. This model provides a new theoretical framework for analysing the collective transfer of information among groups of fishes and other organisms. [ABSTRACT FROM AUTHOR]

An experimental fishway was used to examine adult Pacific lamprey, Lampetra tridentata (Gairdner), behaviour in a series of attraction and passage-performance tests. Among all experiments, lamprey oriented to the fishway floor and walls and were attracted to both ambient and concentrated flow. When confronted with high-velocity areas (vertical-slot and submerged-orifice weirs), many lamprey failed to pass upstream. However, lamprey were able to find and take advantage of low-velocity refuges when they were provided. Lamprey climbed shallow- and steep-angled ramps when attraction cues were sufficient and other passage routes were restricted. The combined results demonstrated the passage challenges that fishways designed and operated for salmonids present to non-salmonid species. They also highlight the importance of evaluating trade-offs between fishway attraction and passage efficiency. The experiments were integrated with tagging studies and development of lamprey-specific passage structures, a research combination that provided an effective template for fishway performance evaluations. [ABSTRACT FROM AUTHOR]

The migration duration of European eel ( Anguilla anguilla) larvae (leptocephali) from the spawning areas in the Sargasso Sea to the European continental shelf remains highly controversial, with estimates varying from 6 months to more than 2 yr. We estimated the fastest migration period and the shortest distance travelled by eel larvae by simulating Lagrangian particles released in the Sargasso Sea and by simulating a range of larval behaviours (fixed-depth drift, vertical diurnal migration and active-depth selection to maximize current velocity). This enabled us to compute (i) a passive drift speed, and (ii) a hypothetic swimming speed needed for European eel larvae to cross the Atlantic in 6 months (i.e., the migration duration estimated from otolith daily growth increments). Our results show that the minimum travel time for an eel larva that is passively drifting was 10 months and 3 days. Active behaviours (vertical diurnal migration and rheotaxis) paradoxically increased the migration period. We found that for leptocephali to cross the Atlantic Ocean in 6 months, they would need to swim a minimum of 3.4 body lengths per second for 8200 km. No larvae have been observed with such swimming capabilities. These results provide evidence that leptocephali cannot cross the Atlantic in 6 months. [ABSTRACT FROM AUTHOR]

The downstream migration of juvenile salmonids has previously been considered predominantly passive. It has been argued that passive displacement during periods of darkness is, partially at least, a result of an inability to maintain a fixed position in the absence of visual cues. In this study, behaviour of juvenile Pacific salmonids was assessed under conditions of light and dark as they passed through an artificial channel and encountered a submerged weir. Results indicated that when light, fish formed schools and actively explored the channel. Conversely, when dark (infrared illumination only) they did not form schools, but maintained randomly distributed positions holding station against the flow. As a consequence, more fish approached and either passed, or rejected, the weir when light. The majority of fish that passed the weir did so within the first minute of each trial. Fish predominantly passed through the channel facing downstream and changed orientation prior to passing tail first over the weir crest in the presence and absence of visual cues. The orientation switch was less common when dark. This study shows, at a fine-resolution scale, that downstream movement of juvenile salmonids can be inhibited as fish exhibit alternative behaviours in the absence of visual cues. Downstream movement was not predominantly passive. Fish passage design should not be based on the assumption that downstream migration is passive. [ABSTRACT FROM AUTHOR]

To better understand migratory divergences among Anguilla anguilla glass eels, the behaviour of individuals caught at the time of their estuary entrance was studied through their response to a light:dark cycle and then to both water current reversal and light:dark cycle. In a first experiment, fish moving with the flow in response to dusk (M+ fish) and fish that had not exhibited any movement (M− fish) were distinguished. Anguilla anguilla from these two groups were then individually marked and their response to water current reversal compared. M+ individuals mainly exhibited negative rheotaxis with a tidal periodicity, whereas positive rheotaxis was mainly exhibited by M− individuals. Thus, M+ A. anguilla glass eels showing negative rheotaxis appear to have the strongest propensity to migrate, the converse applies to M− ones showing positive rheotaxis. A small percentage of individuals (5%) were hyperactive, alternately swimming with and against the current with almost no resting phase. These fish lost c. 2 mg wet mass day−1, whereas individuals which were almost inactive lost c. 1 mg day−1. Wet and dry mass changes in relation to activity levels were compared with previous experiments and it was concluded that A. anguilla glass eel energy status might be involved in differences in migratory tendencies but other factors that might be important are discussed. It is proposed that any decrease in A. anguilla glass eel energy stores associated with global warming might lead to an increase in the proportion of sedentary individuals and thus be involved in the decrease in the recruitment to freshwater habitats. [ABSTRACT FROM AUTHOR]

Epaulette sharks Hemiscyllium ocellatum in three treatments, pit organs (free neuromasts) ablated, sham-operated and normal (n = 8 for each treatment), showed a significant preference for facing upstream in a flume (P < 0·05). There were no significant differences in the mean angles or angular variances among treatments. Individuals with ablated pit organs, however, spent significantly less time moving around than controls (P < 0·05), suggesting that pit organs contributed to motivation for activity. Pit organs do not appear to make an important contribution to rheotaxis in H. ocellatum . It is suggested that this may be due to structural differences in the pit organs of H. ocellatum compared with other species. [ABSTRACT FROM AUTHOR]

The Sitka eddy is a mesoscale eddy, 300 km in diameter, that develops off SE Alaska in about one year in two. The eddy has surface currents exceeding 50 km day-1 and it has been suggested that the eddy could deflect migrating salmon to the south, thereby reducing the proportion of British Columbia (BC) sockeye salmon accessible to Alaskan fishers. We modelled its effects on the migration of sockeye salmon (Oncorhynchus nerka) returning to northern BC, using an individual-based model to simulate migration paths, migration timing and metabolic costs of salmon with different migration behaviours. Except when their migration behaviour included positive rheotaxis, salmon that encountered the eddy had faster migration times and lower metabolic costs than those that did not. The least complex migration behaviour, compass orientation with no rheotaxis, was only slightly less efficient in metabolic terms than the optimal migration paths determined by dynamic programming. Our simulations show that the Sitka eddy itself does not deflect migrating salmon to the south or south-east regardless of migration behaviour, but that by interrupting the normal northward flow of the Alaskan Current, the eddy could influence latitude of landfall of migrating salmon. [ABSTRACT FROM AUTHOR]

Slow currents are known to be an important factor conditioning the habitat of the freshwater snail Biomphalaria glabrata (Say), intermediate host of the human schitosome, Schistosoma mansoni (Sambon). (2)Field studies have shown that a wheatgerm bait can trigger positive rheotaxis in the snail, resulting in upstream migration of much as 30ft/snail/day (Etges & Frick 1966). If the identity and natural sources of these chemicals were known, an improvement in existing control techniques might be made. (3)In this paper laboratory experiments are described in which the aqueous extracts of eight macrophytes and four lettuce cultivars are compared and contrasted in their ability to elicit positive rheotaxis. (4)The results show that attractive chemicals occur in a wide variety of plant species. Some plants, however, yield extracts which elicit little or no rheotactic orientation. Evidence is presented which suggest that, for the emergents Apium nodiflorum (Umbelliferae) and Rorippa nasturtium-aquaticurm (Cruciferae), this difference is attributed to the presence of antagonistic substances, rather than the absence of attractants. (5)The relevance of these findings to the ecology and control of snails is discussed. [ABSTRACT FROM AUTHOR]

Freshwater Amphipoda, migrating upstream in running water, were collected in an automatic trap incorporating a trickle of water to which they react by positive rheotaxis. Some catches with 24-hour intervals as well as some with 2-hour intervals are shown. [ABSTRACT FROM AUTHOR]