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.     

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.     

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.     

Influence of surfagon on rheoreaction of juvenile rainbow trout

The rheoreaction of juvenile rainbow trout (aged 2 months) was studied 30–40 days after a single injection of surfagon (synthetic analogue of gonadotropin-releasing hormone). Individuals subjected to surfagon preferred to move against the water current both in normal and migratory state, while control (not injected) individuals preferred to move downstream. Surfagon strongly modified the rheoreaction of individuals in normal and migratory state.     

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.     

Type of rheoreaction in the early ontogenesis of roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.) as a factor determining its biotopic distribution

The specific features of rheoreaction in roach Rutilus rutilus (L.) larvae from open and protected shallows of the Rybinsk Reservoir have been studied. Data on length and weight of roach sampled at various habitats at B–E developmental stages are presented. It has been revealed that the type of roach larvae rheoreaction is a behavioral mechanism of their distribution over different types of habitats, not only in rivers but also in the waterbodies with slow water turnover rates—lakes and reservoirs. By the time of developmental stage E, this mechanism provides the sustainable spatial separation of juvenile fish, which in the future may lead to intrapopulation differentiation in roach.     

Behavior of trout fry Salmo gairdneri during swinging

Ten experimental and 10 control experiments on a parallel swing and 4 experiments on a rotating stand were carried out on the fries of the trout Salmo gairdneri, strain Rofor. Depending on changes of motor activity the fish could be divided into three groups: the "freezing" fish, in which the mean swimming rate dropped sharply with the beginning of swinging; (2) the shuttle-swimming fish, in which the mean swimming rate in the process of swinging practically did not change, but which with beginning of swinging started the from-wall-towall swimming in the horizontal plane by changing direction of the movement with a frequency close to the swinging frequency; (3) the "restless" fish, in which significant fluctuations of the meanswimming rate were observed. A decrease of the motor activity in the first group fish seems to be a protective reaction. By freezing, they decrease the vestibular apparatus stimulation. Analysis of the available data allows thinking that the shuttle swimming is based on an unconditional rheoreaction characteristic of pelagic fish. Its realization during swinging depends on activity of otolith organs that until now have not been considered a possible sensor for realization of the rheoreaction. Taking into account the principal role of otoliths in this process, we called this rheoreaction variant the otolithotropic reaction. With increase of stimulus strength, the shuttle movement frequency becomes equal to the stimulation frequency. At the same time, sharpness of the otolith reaction is gradually deteriorated, which, however, is not associated with fatigue of the fish. In fish of the third group, the behavioral changes that are as pronounced as those in fish of the two former groups were not revealed. However, it is to find out the character of behavior of this fish group with increase of time and amplitude of the variable acceleration. Thus, we have managed for the first time to describe a new fish reaction to swinging--the otolith reaction and to confirm the conclusion that the swinging affects the fish motor activity. We suggest that a sharp decrease of the mean swimming rate and a disturbance of otolith reaction are signs of the fish motion sickness.     

Behavior of trout fry <Emphasis Type="Italic">Salmo gairdneri</Emphasis> during swinging

Ten experimental and 10 control experiments on a parallel swing and 4 experiments on a rotating stand were carried out on fries of the trout Salmo gairdneri, strain Rofor. Depending on changes of motor activity the fish can be separated into three groups: (1) the “freezing” fish, in which the mean swimming rate dropped sharply with the beginning of swinging; (2) the shuttleswimming fish, in which the mean swimming rate in the process of swinging practically did not change, but which with beginning of swinging started the from-wall-to-wall swimming in the horizontal plane by changing direction of the movement with a frequency close to the swinging frequency; (3) the “restless” fish, in which significant fluctuations of the mean swimming rate were observed. A decrease of the motor activity in the first group fish seems to be a protective reaction. By “freezing,” they decrease the vestibular apparatus stimulation. Analysis of the available data allows thinking that the shuttle swimming is based on an unconditional rheoreaction characteristic of pelagic fish. Its realization during swinging depends on activity of otolith organs that until now have not been considered a possible sensor for realization of the rheoreaction. Taking into account the principal role of otoliths in this process, we called this rheoreaction variant the otolithotropic reaction. With increase of stimulus strength, the shuttle movement frequency becomes equal to stimulation frequency. At the same time, sharpness of the otolith reaction is gradually deteriorated, which, however, is not associated with the fatigue of the fish. In fish of the third group, the behavioral changes that are as pronounced as those in fish of the two former groups were not revealed. However, the character of behavior of this fish group with increase of time and amplitude of the variable acceleration is to be elucidated. Thus, we have managed for the first time to describe a new fish reaction to swinging—the otolith reaction and to confirm the conclusion that the swinging affects the fish motor activity [1]. We suggest that a sharp decrease of the mean swimming rate and a disturbance of otolith reaction are the signs of the fish motion sickness.     

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).     

Kin and familiarity influence association preferences and aggression in the mangrove killifish Kryptolebias marmoratus

Association preferences and aggression intensity were investigated in relation to kin and familiarity in the self-fertilizing, clonal vertebrate, the mangrove killifish Kryptolebias marmoratus. Results indicated that fish preferentially associated with and exhibited less intense aggression towards members of their own genotype (kin), compared to members of a different genotype (non-kin). Furthermore, when fish were presented with stimulus groups of the same genotype that were familiar or unfamiliar, fish preferentially associated with and exhibited lower aggression intensity directed towards familiar groups. These results indicate that this species prefer to associate with both kin and familiar individuals and modulate aggression accordingly. These results are discussed with reference to the adaptive benefits of kin recognition and preferences for familiars, and place results within the context of current knowledge of the ecology of K. marmoratus.     

Fish preference for hydraulic habitat in typical middle reaches of Yangtze River,China

This study presents a method of combining hydroacoustics and hydraulic data to estimate fish preference in a large and rapidly flowing river system. A typical middle reach of the Yangtze River with three islands and two wandering sections was taken as the research object to interpret schools of fish with different sizes and densities for their preference of physical habitat features such as water depth and velocity by using Geographic Information Systems (GIS). Fish density and size were determined based on the hydroacoustic data, and hydraulic variables were simultaneously collected using an Acoustic Doppler Current Profiler (ADCP) system. Results show that fish sizes are correlated with water depth and velocity and that fish density correlated only with water depth. Small fish prefer high water depth average velocity (WDAV), lower vertical average velocity (VAV), deep water, as well as a wide depth and velocity range; large fish prefer low WDAV, high VAV, deep water, and a narrow depth and velocity range. High fish densities appear around islands and areas with deep water. The results show that large fish may be sufficiently strong enough to select their preference for water depth and velocity. Areas of deep water can provide broad velocity diversity and more space to accommodate fish. The island littoral zone could provide a variety of habitats with a diverse pattern of depth and velocity for fish. This study provides a contributive method for the field habitat suitability assessment for fish.     

Experimental study of larval efficiency of Gambusia affinis holbrooki (GIRARD, 1859) (fish-Poecilidae)

Experimental study of efficiency of Gambusia affinis holbrooki (GIRARD, 1859) (Fish-Poecilidae). Gambusia affinis is a culiciphage fish which was introduced in Tunisia in 1929 to control mosquito larvae. In the present study, we confirm, under laboratory conditions, the good efficacy of Gambusia affinis against mosquito larvae. The consumption of larvae decreases with the evolution of larvae instars and increases, for the same instar, in relation with the fish size. In fact, the size of the prey is related to the predator's size: fish belonging to the length class [20-24 mm] prefer IIIrd instar, fish from class length [25-29 mm] prefer pupae and IVth instar. The trophic test shows that G. affinis has a clear preference for Culicidae larvae, except fish belonging to the 2 length classes [35-39 mm] and [40-44 mm] for which Culicidae and Ephemeroptera have similar preference. In addition, at high temperature (30 degrees C), Gambusia affinis has a higher efficiency.     

Comparison of behavioral and physiological–biochemical indices in fingerlings of roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.) from the Ild River and Ild Bay in the Rybinsk Reservoir

It is found that the size–mass, physiological–biochemical, and behavioral parameters in roach fingerlings from the upper and lower (mouth) reaches of the Ild River differed during the autumn season. Compared with the roach from the upper reach of the river, the fingerlings of the same age from the mouth part have larger lengths and weights and a higher concentration of cations in the body. In experiments, the fish from the mouth part selected a lower (~4°C) temperature and showed a lower resistance to the water flow. The reason for differences in behavioral responses in two groups of juveniles of roach is probably, on the one hand, their physiological and biochemical characteristics and, on the other hand, the motivational component of fish behavior in different environments—hydrological, thermal, and hydrochemical conditions and different food items in geographically remote parts of the same river. It is assumed that in autumn roach fingerlings migrate from the littoral of the mouth part of the river into deeper parts under a decrease in water temperature before the downstream migration of the fingerlings in the rivers. This is probably due to the earlier achievement of the migration status of fingerlings from the mouth part than that in fish from the upper reach of the river and due to the peculiarities of their physiological state. Negative rheoreaction, manifested in the experiment in ~80% of the fish from the bay of the reservoir and ~55% of the fish from river, confirms the fish readiness to migrate and is likely due to the behavioral mechanism of fish migration from the littoral and downstream the river.     

Choice of feeding station in Atlantic salmon, Salmo salar, parr: effects of predation risk, season and life history strategy

The current speed at which underyearling salmon parr held feeding stations was examined from late summer to early winter in laboratory flume tanks that offered a choice between (a) areas with high water flow, high food availability but high predation risk and (b) areas with low flow, little food but shelter from predators. In August, those fish that would become smolts aged 1 + (and which by late winter formed the upper modal group, UMG, of the bimodal size distribution) adopted positions in faster currents than did the fish which would take a further year to reach the smolt stage (the lower modal group, LMG). However, the chosen current speed of UMG fish decreased through the period of study, so that by December all fish were found in areas of low flow, and hence little food. Both date and water temperature had independent effects on the chosen current speed of UMG fish.
The effect of predation risk was investigated using a model trout. A brief sight of this predator caused 47% of fish that had been in the main, exposed currents to move to slacker, sheltered areas; they took 1 h, on average, to return to their previous position. The fish that remained in position upon seeing the predator reduced their rate of tail beating, presumably increasing crypticity. Eventual UMG parr were less likely than were LMG fish to move away upon seeing a predator. The fish moved to faster currents than normal 2–3 h after seeing the predator, possibly compensating for the earlier reduction in feeding rate.     

Effect of methyltestosterone on physiological state and rheoreaction of rainbow trout <Emphasis Type="Italic">Parasalmo mykiss</Emphasis> (=<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) under unfavorable keeping conditions

The effect of methyltestosterone given with feed during one and two months on the state of gonads, the level of thyroid, and sex steroid hormones in blood and on rheoreaction is studied in juvenile rainbow trout Parasalmo mykiss (=Oncorhynchus mykiss) raised under unfavorable conditions (tropics, Vietnam). In comparison with the control, in the experimental group, the part of sterile specimens was higher (83 vs. 35%), the part of males was lower (17 vs. 40%), while females and hermaphrodites were absent. At prolonged starvation (12 days), the experimental specimens demonstrated lower increase of the level of thyroid and sex steroid hormones in blood than that in the control specimens. Methyltestosterone modified the behavior of rainbow trout in water flow: delivery of the hormone in food during 1 month increased the part of fish moving against the flow and suppressed movement both upstream and downstream during 2 months. Thus, methyltestosterone negatively influences the physiological condition and adaptation capacity of rainbow trout.     

How should a clever baboon choose and move rocks?

Chacma baboons (Papio ursinus) intentionally overturn rocks to feed on the invertebrates beneath. However, baboons do not move all the rocks they encounter, with this presumably reflecting cost–benefit (or effort–reward) trade‐offs in their foraging behavior. We ask, how do “clever baboons” choose rock sizes and shapes and move these rocks? Using optimal foraging theory, we predicted that baboons would prefer to move medium‐sized rocks, a trade‐off between moving larger rocks that might require more effort to move, and smaller rocks that likely do not provide enough prey (the reward) to make the effort worthwhile. We also expected baboons to prefer rounded rocks as these will require less energy to move by rolling (rather than being flipped as for flat rocks) and that the effort of rock movement might be offset by moving rocks along the shortest axis. We show that baboons have clear preferences for specific rock sizes (medium‐sized) and shapes (angular and flat when these were medium‐sized), and the way in which rocks are moved (along the shortest axis). Prey occurred infrequently under rocks. The low predictability of prey beneath rocks suggests that such prey, when encountered, is of considerable value to baboons for them to expend the search effort, and also explains the extensive nature of rock movement by baboons in the landscape. Our study provides a novel application of the optimal foraging theory concept and has important implications for understanding and predicting how animals choose to move rocks.     

Distribution,population structure,and some biological distinctions of pikeperch <Emphasis Type="Italic">Sander lucioperca</Emphasis> of the channel part of the Akhtuba River (Volga-Akhtuba water system)

Biological traits (distribution, reproduction, age composition, body length and weight) of pikeperch Sander lucioperca from channel parts of the Akhtuba River, remote from the Volga Delta, are investigated. In the investigated stretch of the river, movements of most specimens of pikeperch are local and occur in the deep part (4?10 m) of the channel. Aggregations of fish are not confined to any definite points but move along the extensive stretch of broads. Pikeperch prefer near-bottom biotopes confined to the zone of stable hydrodynamic eddies in places of complicated bottom relief—transverse crests and longitudinal channel crests. For the first time, it is found that pikeperch in the under-ice period move to the shallow zone of submersed inshore shrubs. The age structure and body length and weight of pikeperch differ from those in the Volga Delta and correspond more to the populations from northern and northwestern parts of the species area. Pikeperch spawn only in temporary water bodies of the accessory system, within a short period at the temperature 11?17°С. The data on biology of pikeperch from the Akhtuba channel indicate the populational level of differences from the Volga Delta pikeperch.     

Water velocity shapes fish movement behavior

Stream and river ecosystems present fluvial fishes with a dynamic energy landscape because moving water generates heterogeneous flow fields that are rarely static in space and time. Fish movement behavior should be consistent with conserving energy in these dynamic flowing environments, but little evidence supporting this hypothesis exists. Here, we tested experimentally whether three general movement behaviors—against the current, with the current, or holding position (i.e., staying in one position and location)—were performed in a way consistent with minimizing the cost of swimming in a heterogeneous flow field. We tested the effects of water velocity on movement behavior across three age classes (0, 1, and 5 years) of two different fluvial specialist fishes, the pallid sturgeon (Scaphirhynchus albus) and shovelnose sturgeon (Scaphirhynchus platorynchus). Individuals from the three age classes were exposed to a continuous and dynamic velocity field ranging from 0.02 to 0.53 m s⁻¹, which represented natural benthic flow regimes occupied by these species in rivers. Both sturgeon species exhibited the same pattern with regard to their tendency to hold position, move upstream, or move downstream. Moving downstream was positively associated with velocity for all age groups. Moving upstream was inversely related to velocity for young fish, but as the fish aged, moving upstream was not related to water velocity. The oldest fish (age 5) moved upstream more frequently compared to the younger age classes. Holding position within a water current was the most frequent behavior and occurred with similar probability across the range of experimental velocity for youngest fish (age 0), but was inversely related to velocity in older fish. Our experiment across age classes suggests that the suite of swimming behaviors exhibited by fluvial specialists might have evolved to mitigate the energetic costs of complex energy landscapes generated by moving water to ultimately maximize net energy gain.     

Distribution, growth and movement of River Usk brown trout (Salmo trutta)

The River Usk catchment in South Wales supports mainly freshwater resident brown trout, with few anadromous fish. Electric fishing and netting revealed that age-class distribution differed between main river and tributary habitats, the latter environment acting as a nursery area for young fish. Few fry were found at main river sites. Age-class distribution also differed between tributary systems, and possible reasons are discussed. Trapping experiments indicated that trout move to main river habitat at 2+ yr. Lengths at age (back-calculated from scale reading) were similar for main river and tributary resident fish at 1 and 2 year, but main river fish were larger at 3 and 4 yr. This habitat shift and size difference is discussed with reference to current angling regulations.     

Effect of Diet Change on Rheoreaction in Young Rainbow Trout Oncorhynchus mykiss

Journal of Ichthyology - The motivational component of rheoreaction has been determined in 4-month-old juvenile rainbow trout Oncorhynchus mykiss on different diets. It is shown that the diet...