Surfagon Effect on Rheoreaction of Young Brown Trout Salmo trutta

Journal of Ichthyology - The effect of surfagon injection (synthetic analog of gonadotropic-releasing hormone) on the kind and time of rheoreaction change in juvenile brown trout Salmo trutta is...     

On methods of determination of the rheoreaction type in fish

Type of rheoreaction is investigated in some species of salmonids, cyprinids, and percids. Three types of rheoreaction are discerned: positive (the fish prefer to move against the current), static (the fish retain their position in the current), and negative (the fish prefer to move downstream). It is shown that the type of rheoreaction is probabilistic and is determined by the motivational state of fish. Procedures used in investigation of the rheoreaction type are discussed.     

Rheoreaction as a mechanism of formation of phenotypic groups of underyearlings of the Atlantic salmon <Emphasis Type="Italic">Salmo salar</Emphasis>

Experimental investigation on rheoreaction as a behavioral mechanism in the formation of phenotypic groups of underyearlings of the Atlantic salmon Salmo salar is performed. Juveniles of the Atlantic salmon are investigated at the age 0+ from the coastal group and from the tributary group in the period of its primary distribution from redds. The underyearlings from the tributary group differ from the coastal fish in increased critical current velocity, the fact that among them the most portion of individuals have a positive type of rheoreacrtion, and the fact that they prefer currents more often. The behavioral mechanism of spatial separation of the spreading juveniles at confluence of two currents is revealed: stronger individuals with the positive type of rheoreaction and the expressed rheopreferendum mainly move against the flow at a higher speed and manage to get into a tributary. The weaker fish with static and negative dynamic types of rheoreaction, having no expressed rheopreferendum, prefer the flow with lower current rate and turn out to be in the coastal zone of the mainstream.     

Estimation of Surfagon Influence on the Gonadal State of Rainbow Trout <Emphasis Type="Italic">Parasalmo mykiss</Emphasis> (=<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) Juveniles at the Background of Temperature Stress

Regulatory effect of surfagon—a synthetic analog of gonadotropin-releasing hormone—on the gonad state of rainbow trout (Kamchatka steelhead Parasalmo mykiss (=Oncorhynchus mykiss)) juveniles is investigated. The juveniles were 2.5 months old and were exposed to brief (4 days) heat stress (19–20°C). The increase of water temperature was followed by anomalies of gonads after 1 month (destruction of sex cells and hypertrophy of connective tissue). In females, the increased water temperature activates sex redetermination: in ovaries, cysts containing destroyed spermatogonia are found. In 1.5 months, the exogenous application of surfagon was followed by acceleration of spermatogenesis in gonads of experimental fish (2.5 months old) and by a slight decrease of fraction of anomalies in structure of their testes compared with the gonads of fish not exposed to surfagon. Exposure of rainbow trout to surfagon prior to sex differentiation is more efficient than after it is completed.     

Patterns of movements of fish with negative type of rheoreaction

Experiments carried out on underyearlings of four fish species—roach Rutilus rutilus, carp Cyprinus carpio, bream Abramis brama, and perch Perca fluviatilis—at illumination of 200–300 lx showed that the specimens with negative type of rheoreaction move downstream mainly (47–93%) in the active form, with their heads downstream, and rarer (3–37%) in the active-passive form, with their tails downstream. Increase of motivation for downstream movement caused by starvation leads to a higher part of fish with an active form of movement and to greater speed of movement of underyearlings. Active downstream movement is a manifestation of rheoreaction.     

Rheoreaction type of early juveniles of sockeye salmon Oncorhynchus nerka in the Ozernaya River and Lake Kurilskoe

Rheoreaction of early juveniles of sockeye salmon Oncorhynchus nerka is experimentally investigated, including different spatial groups (denatant migrants, contranatant migrants, specimens living in bays and at closed river banks, juveniles from the coastal zone of the lake). Investigation is made in water of the river flowing from the lake and in water of the stream flowing into the lake. It is shown that the rheoreaction (the type of rheoreaction) is one of behavioral mechanisms performing feeding migration of early juveniles of sockeye salmon. Contranatant migrants that reached the feeding lake retain the positive type of rheoreaction, which favors the exit of juveniles from the zone of discharge exclusion and prevents the drift of juveniles to the river at night at poorer conditions for orientation. Juveniles placed into the water of the inflowing stream manifest a sharply negative rheoreaction type contributing to their rapid lakeward migration for feeding. In water of two steams (taking its beginning in the lake and flowing into it) such type of rheoreaction is observed which ensures migration of sockeye juveniles to their principal feeding water body-Lake Kurilskoe.     

Condition of Sex Glands in the Young of the Current Year of Rainbow Trout Subjected to Surfagon Injections

Condition of sex glands and thyroid and steroid hormone levels in the blood are assessed in the young of the current year of rainbow trout cultivated in the high-mountain area of South Vietnam and subjected to injections of surfagon (synthetic analogue of gonadotropin-releasing hormone). In the conditions of the trout hatchery (Vietnam), gonads of the young of the current year are characterized by substantial anomalies, including an appearance (in addition to females and males) of hermaphrodite and sterile individuals. A single injection of surfagon 1 month after hatching leads to stabilization of the development of sex glands and decrease of the proportion of sterile individuals (from 41 to 22%). This study is the first attempt of the assessment of the effect of the injection of gonadotropin-releasing hormone analogue on the development of sex glands in the early ontogeny of fishes.     

Development and application of methods for investigating the ratio of rheoreaction types of fish in a circular tank

Methods for evaluating the motivational component of the fish rheoreaction (ratio of rheoreaction types) are developed and tested in a circular hydrodynamic tank for three fish species (Danio rerio, Poecilia reticulata, and Inpaichthys kerri). Three rheoreaction types of fish were distinguished: a positive type (fish movements against water current), a negative type (fish movements along with water current), and a compensatory type (fish maintaining their position in relation to immobile reference points). The main distinguishing features of these new methods are unrestricted distance for fish movements, continuous monitoring of individual fish movements (video recording), and evaluation of ratio between the types of rheoreaction in terms of duration of demonstration of these types by each. The minimum required observation time and water current velocities are determined. It is shown that these methods can be used for investigating the types of rheoreaction in different fish species. Every single individual repeatedly demonstrated all these three rheoreaction types during the test.     

Neurotropic effects of luliberin analog in rats with different sensitivity to ethanol]

Luliberin's analogue (surfagon) has been established to activate shock-induced aggression of short-sleeping (SS) and long-sleeping (LS) rats in painful stress. The using of the castration and hypophysectomy has proved this effect to result from the direct neurotropic action of peptide. It has been shown, that SS rats differ from LS ones by more expressed reducing of painful aggressive and reference reactions after castration and hypophysectomy as well as by definitive peculiarities of peptidergic effects of surfagon.     

Effect of the intraventricular administration of gonadotropin-releasing hormone analogue on immune response and unspecific resistance in rats

Intraventricular administration of the synthetic analogue of gonadotropin-releasing hormone (surfagon) results in increased humoral immune response and neutrophile activation including phagocytic and special functional indices in rats. Since testosterone blood level is not changed it may be concluded that the surfagon effect is mediated by nervous mechanisms. The conclusion is also confirmed by the obtained data of the brain stress-limiting system activation manifested by the decrease of oxidative stress.     

The effect of the synthetic analogue of gonadoliberin on immune response and factors of nonspecific resistance in rats and mice

Gonadotropin-releasing hormone's synthetic analogue (surfagon) injected intraperitoneally exerted a dose-dependent influence on humoral immune response values in rats and on phagocytic and functional activity of neutrophiles in mice. Castration induced a reliable decrease of the immune response and character. It may be concluded that the surfagon effect is not mediated by steroids.     

Seasonal niche-tracking behaviour of two partially migratory passerines

Migratory birds spend periods of the year in different locations as a response to seasonal changes in environmental suitability. They are classified as either ‘niche-trackers’ or ‘niche-switchers’, depending on whether they track or switch environmental conditions throughout the year. However, the relationship between these strategies and their migratory behaviour is still unclear. Here we examine whether migratory European Robins Erithacus rubecula and Eurasian Blackcaps Sylvia atricapilla track environmental conditions between breeding and wintering areas and whether their behaviour differs from that of their sedentary counterparts. We used ringing data for both migratory and sedentary individuals wintering sympatrically in the Iberian Peninsula to assess the environmental conditions relating to their seasonal distributions. We explored seasonal niche-tracking using two multivariate analyses with alternative sets of predictor variables (landscape and climate) to generate different environmental scenarios. Our results show that migratory individuals track similar climatic conditions throughout their seasonal distributions, whereas sedentary birds cope with great variation in climate over the course of the year. In addition, migratory birds show less seasonal overlap in the landscape structure of their chosen habitats compared with sedentary individuals. These results suggest that there is a trade-off between, on the one hand, the cost for migrants of travelling long distances and, on the other, the increased flexibility required by sedentary birds if they are to tolerate a wider suite of environmental conditions within their permanent ranges. Given that sedentary populations in the southern Iberian Peninsula seem to be linked to populations of migratory individuals of these two species that started to move northwards after the last glacial cycle, the observed patterns suggest that migrant birds represent a fraction of the southern population that is specialized in the exploitation of a narrower range of environmental conditions.     

Assessing year-round habitat use by migratory sea ducks in a multi-species context reveals seasonal variation in habitat selection and partitioning

Long-distance migration presents complex conservation challenges, and migratory species often experience shortfalls in conservation due to the difficulty of identifying important locations and resources throughout the annual cycle. In order to prioritize habitats for conservation of migratory wildlife, it is necessary to understand how habitat needs change throughout the annual cycle, as well as to identify key habitat sites and features that concentrate large numbers of individuals and species. Among long-distance migrants, sea ducks have particularly complex migratory patterns, which often include distinct post-breeding molt sites as well as breeding, staging and wintering locations. Using a large set of individual tracking data (n = 476 individuals) from five species of sea ducks in eastern North America, we evaluated multi-species habitat suitability and partitioning across the breeding, post-breeding migration and molt, wintering and pre-breeding migration seasons. During breeding, species generally occupied distinct habitat areas, with the highest levels of multi-species overlap occurring in the Barrenlands west of Hudson Bay. Species generally preferred flatter areas closer to lakes with lower maximum temperatures relative to average conditions, but varied in distance to shore, elevation and precipitation. During non-breeding, species overlapped extensively during winter but diverged during migration. All species preferred shallow-water, nearshore habitats with high productivity, but varied in their relationships to salinity, temperature and bottom slope. Sea ducks selected most strongly for preferred habitats during post-breeding migration, with high partitioning among species; however, both selection and partitioning were weaker during pre-breeding migration. The addition of tidal current velocity, aquatic vegetation presence and bottom substrate improved non-breeding habitat models where available. Our results highlight the utility of multi-species, annual-cycle habitat assessments in identifying key habitat features and periods of vulnerability in order to optimize conservation strategies for migratory wildlife.     

Wind selection and drift compensation optimize migratory pathways in a high-flying moth

Numerous insect species undertake regular seasonal migrations in order to exploit temporary breeding habitats [1]. These migrations are often achieved by high-altitude windborne movement at night [2-6], facilitating rapid long-distance transport, but seemingly at the cost of frequent displacement in highly disadvantageous directions (the so-called "pied piper" phenomenon [7]). This has lead to uncertainty about the mechanisms migrant insects use to control their migratory directions [8, 9]. Here we show that, far from being at the mercy of the wind, nocturnal moths have unexpectedly complex behavioral mechanisms that guide their migratory flight paths in seasonally-favorable directions. Using entomological radar, we demonstrate that free-flying individuals of the migratory noctuid moth Autographa gamma actively select fast, high-altitude airstreams moving in a direction that is highly beneficial for their autumn migration. They also exhibit common orientation close to the downwind direction, thus maximizing the rectilinear distance traveled. Most unexpectedly, we find that when winds are not closely aligned with the moth's preferred heading (toward the SSW), they compensate for cross-wind drift, thus increasing the probability of reaching their overwintering range. We conclude that nocturnally migrating moths use a compass and an inherited preferred direction to optimize their migratory track.     

Temporal dynamics of migration‐linked genetic variation are driven by streamflows and riverscape permeability

Landscape permeability is often explored spatially, but may also vary temporally. Landscape permeability, including partial barriers, influences migratory animals that move across the landscape. Partial barriers are common in rivers where barrier passage varies with streamflow. We explore the influence of partial barriers on the spatial and temporal distribution of migration‐linked genotypes of Oncorhynchus mykiss, a salmonid fish with co‐occurring resident and migratory forms, in tributaries to the South Fork Eel River, California, USA, Elder and Fox Creeks. We genotyped >4,000 individuals using RAD‐capture and classified individuals as resident, heterozygous or migratory genotypes using life history‐associated loci. Across four years of study (2014–2017), the permeability of partial barriers varied across dry and wet years. In Elder Creek, the largest waterfall was passable for adults migrating up‐river 4–39 days each year. In this stream, the overall spatial pattern, with fewer migratory genotypes above the waterfall, remained true across dry and wet years (67%–76% of migratory alleles were downstream of the waterfall). We also observed a strong relationship between distance upstream and proportion of migratory alleles. In Fox Creek, the primary barrier is at the mouth, and we found that the migratory allele frequency varied with the annual timing of high flow events. In years when rain events occurred during the peak breeding season, migratory allele frequency was high (60%–68%), but otherwise it was low (30% in two years). We highlight that partial barriers and landscape permeability can be temporally dynamic, and this effect can be observed through changing genotype frequencies in migratory animals.     

Drivers and consequences of partial migration in an alpine bird species

1. Partial migration, where a portion of the population migrates between winter and summer (breeding) areas and the rest remain year‐round resident, is a common phenomenon across several taxonomic groups. Several hypotheses have been put forward to explain why some individuals migrate while others stay resident, as well as the fitness consequences of the different strategies. Yet, the drivers and consequences of the decision to migrate or not are poorly understood.
2. We used data from radio‐tagged female (n = 73) willow ptarmigan Lagopus lagopus in an alpine study area in Central Norway to test if (i) the decision to migrate was dependent on individual state variables (age and body weight), (ii) individuals repeated migratory decisions between seasons, and (iii) the choice of migratory strategy was related to reproductive success.
3. Partially supporting our prediction that migratory strategy depends on individual state, we found that juvenile birds with small body sizes were more likely to migrate, whereas large juveniles remained resident. For adult females, we found no relationship between the decision to migrate or stay resident and body weight. We found evidence for high individual repeatability of migratory decision between seasons. Migratory strategy did not explain variation in clutch size or nest fate among individuals, suggesting no direct influence of the chosen strategy on reproductive success.
4. Our results indicate that partial migration in willow ptarmigan is related to juvenile body weight, and that migratory behavior becomes a part of the individual life history as a fixed strategy. Nesting success was not affected by migratory strategy in our study population, but future studies should assess other traits to further test potential fitness consequences.

     

Effect of a luliberine analogue (surfagon) on food conditioning in rats with different sensitivity to ethanol

Food conditioning worsened following a luliberine analogue surfagon administration in short-sleeping (SS) rats. Castration mostly inhibited the peptide effect. The findings suggest a possibility of the peptide effect occurring even without steroids.     

The social context of cannibalism in migratory bands of the Mormon cricket

Cannibalism has been shown to be important to the collective motion of mass migratory bands of insects, such as locusts and Mormon crickets. These mobile groups consist of millions of individuals and are highly destructive to vegetation. Individuals move in response to attacks from approaching conspecifics and bite those ahead, resulting in further movement and encounters with others. Despite the importance of cannibalism, the way in which individuals make attack decisions and how the social context affects these cannibalistic interactions is unknown. This can be understood by examining the decisions made by individuals in response to others. We performed a field investigation which shows that adult Mormon crickets were more likely to approach and attack a stationary cricket that was side-on to the flow than either head- or abdomen-on, suggesting that individuals could reduce their risk of an attack by aligning with neighbours. We found strong social effects on cannibalistic behaviour: encounters lasted longer, were more likely to result in an attack, and attacks were more likely to be successful if other individuals were present around a stationary individual. This local aggregation appears to be driven by positive feedback whereby the presence of individuals attracts others, which can lead to further crowding. This work improves our understanding of the local social dynamics driving migratory band formation, maintenance and movement at the population level.     

Behavioral differentiation of underyearlings of the Black Sea salmon <Emphasis Type="Italic">Salmo trutta labrax</Emphasis>: Rheoreaction in the year preceding smoltification

Hatchery rearing underyearlings of the Black Sea salmon Salmo trutta labrax at the age of five-six months (nine-ten months before the beginning of smoltification) divide into two spatial groups—bottom group and pelagic group. This is caused by lack of territory (bottom area): the minority of fish are bottom-dwelling—such fish are territorial, they extrude the majority of individuals to the water column. It is determined experimentally that the bottom-dwelling fish belonging to the bottom group, in comparison with the fish of pelagic group, are characterized by higher critical flow velocities and lower locomotor activity in the rheogradient. Part of individuals with the static type of rheoreaction among them is higher. The fish from the pelagic group do not have such resource as individual territory. This fact modifies the probability of manifestation of resident and migrant behavior after starvation (during ten days). The individuals from the pelagic group demonstrate the behavior characteristic of future migrants (downstream movement) to a higher degree. The individuals from the bottom group, in comparison with pelagic fish, demonstrate, to a great degree, behavior typical for future residents (upstream movement).     

Migrating Birds as Dispersal Vehicles for West Nile Virus

Whereas migrating birds have been implicated in the spread of West Nile virus (WNV), there is no direct evidence of birds actively migrating while infectious. The role of birds in WNV dispersal is difficult to assess in the field. However, this role can be evaluated experimentally because birds in migratory disposition display increased locomotor activity or restlessness under captive conditions. We tested the following hypotheses: (1) migrating passerine birds continue to exhibit migratory activity while infectious with WNV and (2) the migratory state of the individual affects the magnitude of viremia. We examined the migratory activity of two neoarctic-neotropical passerine migrants, Swainson’s thrush (Catharus ustulatus) and gray catbird (Dumetella carolinensis), during acute WNV infection. All gray catbirds and six of nine Swainson’s thrushes exhibited migratory activity while infectious. Moreover, migratory status did not appear to influence viremia titers, as might be expected if individuals were immunosuppressed during migration. Therefore, we demonstrate that migrating passerine birds are potential dispersal vehicles for WNV.