Microhabitats and diel downstream migration of young grayling (Thymallus thymallm L.)

SUMMARY. 1, Microhabitats chosen by young grayling ( Thymallus thymallus L.) were investigated by electrofishing. The first feeding habitat was marginal areas where water velocity did not exceed 15 cms⁻¹. Fry fed on drift in the first 10 cm of the water column below the surface. This location was very stable during the first weeks of growth (mid-April to mid-May). When they were 3–3.5 cm long, fry began using benthic areas and gradually moved away from the banks towards the channel.
2. A downstream migration was noted from the beginning of emergence (mid-April) to the end of May. This mainly nocturnal movement involved all fish sizes and caused a complete removal of young-of-the-year by June from the spawning tributary.     

Migration of smolts of Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta L.) in a chalkstream

Synopsis Migration of smolts in the River Piddle, Dorset, was studied over three years in relation to factors that could influence downstream movement. The river originates mostly from groundwater springs, resulting in stable flows and low turbidity except in very rainy weither. Fish were intercepted at the tidal limit in a fixed trap-net, and measurements of water temperature, discharge, turbidity, barometric pressure, rainfall and solar radiation taken nearby. Slightly increased turbidity and discharge following heavy rain initiated major movements during two nights of the total of 55 days studied. At other times large-scale movements rock place during sunny warm afternoons. Both solar radiation and water temperature were correlated with intensity and timing of movement. The pattern of migration is different from that reported on other rivers, reflecting the relatively stable flow regime of the chalkstream.     

The influence of water velocity on the downstream movement of alevins and fry of brown trout, Salmo trutta L.

Trout eggs were planted in four experimental stream channels, each channel being run at a different but constant discharge. Survival of the eggs to hatching was low and apparently unrelated to surface water velocity. However, movement of young trout out of channels was affected by water velocity, the higher the velocity the greater the proportion of trout that were lost. Virtually all fry moved out of a channel with a mean surface water velocity of 0.73 m s⁻¹. The rate of loss was not constant over the experiment but increased as the young trout entered the free-feeding stage. At the end of the experiment loss of fry, after abrupt increases in discharge, was demonstrated in the lower velocity channels.     

Stream channel experiments on downstream movement of recently emerged trout, Salmo trutta L., and salmon, S. salar L.—111. Effects of developmental stage and day and night upon dispersal

Four experimental stream channels were used to examine the temporal pattern of downstream dispersal of young salmon and trout at four constant water velocities from the time of emergence from the gravel onwards.
At low water velocities ( c . 8.0 cm s ⁻¹) young salmon showed a high rate of dispersal which was maintained until a very low population density was attained. At higher velocities salmon showed a lower rate of dispersal and the final population density was higher. Trout showed a low dispersal rate at low velocity and higher rates at higher velocities. However, the final trout population density was similar at all water velocities because the low dispersal rate observed at the low velocity persisted for a much longer period than did the higher values at the higher water velocities. The results do not support the view that young salmonids have a narrow and definable period of sensitivity to water velocity.
Dispersal rates were significantly higher by night than by day (P <0.001) at all velocities for both fish species.     

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.     

Movement rhythms in juvenile Atlantic salmon, Salmo salar L.

Nocturnal downstrean migration of juvenile Atlantic salmon is usually interpreted as increased locomotor activity. The frequency of downstream passages of 0–1 + salmon in an endless stream channel was greater by night than by day in both smoking and non-smolting fish in autumn and spring. Movement increased at dusk, and decreased after dawn. Mature male 1 + fish moved slightly less than immatures in October, but significantly more in November. Total movement frequency was lower at full moon than at other moon phases, and movement was reduced when the moon was up. Under turbid conditions by day, the threshold water velocity inducing nett downstream movement was 8.2 cm s⁻¹, and the relative velocity of fish swimming downstream was never more than one third that of fish holding station at the normal maximal flow of 25–30 cm s⁻¹.
At the end of their first growing season in October, fish which had been offered food continuously through 24 h did not differ in size from those fed by day only, but the latter were significantly larger than those offered food only at night.
We conclude that: (1) the fish fed actively by day, and not by night; (2) station-holding represented activity, and downstream nocturnal movement represented relative inactivity (displacement) which occurred on loss of visual orientation, hence migration resulted from reduced activity; (3) lack of displacement in early autumn has adaptive value for maturing fish, but not for non-spawners.     

Stream channel experiments on downstream movement of recently emerged trout, Salmo trutta L., and salmon, S. salar L.—11. Effects of constant and changing velocities and of day and night upon dispersal rate

Four experimental stream channels were used to study instantaneous downstream dispersal rates of young trout and salmon relative to day and night, constant low and high water velocities and changes of velocity from high to low and vice versa.
At high and low velocity for trout and at high velocity for salmon, the dispersal rate was higher by night than by day. Changes of velocity during daytime from high to low or low to high for trout and from high to low for salmon, were associated with much higher dispersal rates than were constant velocities.     

Stream channel experiments on downstream movement of recently emerged trout, Salmo trutta L. and salmon, S. salar L.—I. Effect of four different water velocity treatments upon dispersal rate

Four experimental stream channels were used to study instantaneous downstream dispersal rates of young trout, Salmo trutta L., and salmon, S. salur L ., relative to four different water velocities.
Young salmon showed a high rate of dispersal at a low velocity of 7.5 cm s⁻¹ and lower rates at higher velocities of 25 to 70cm s⁻¹. Trout showed their lowest rate at 25cm s⁻¹ with a slightly higher rate at 7.5 cm s⁻¹ and increasingly higher rates at velocities in excess of 25 cm s⁻¹. These results are consistent with field observations on the velocity preferences of young trout and salmon.     

OBSERVATIONS ON THE ROOT ANATOMY OF RICE (ORYZA SATIVA L.)

Rice plants were grown hydroponically and roots were prepared for light and electron microscopy using standard techniques. The roots are bounded by an epidermis, exodermis, and fibrous layer. The exodermis has a suberin lamella along its inner tangential wall. The fibrous layer is composed of thick-walled lignified cells with little pitting. The cortical parenchyma is compact when young, but expands and separates to form a zone of cell walls and air spaces in a spoked arrangement. Supporting columns of living parenchyma cells are occasionally present, particularly near lateral roots. The endodermis is typical for grasses with Casparian strips, suberin lamellae, and tertiary state walls with numerous pits. The pericycle and pith become sclerified. Protoxylem elements alternate with protophloem in the young root; later, early metaxylem, late metaxylem, and metaphloem proliferate. The exodermis, fibrous layer, lacunate cortex, and endodermis appear to present a formidable barrier to radial ion movement in the mature portions of the root.     

Transitions in nutation trajectory geometry in peppermint (Mentha x piperita L.) with respect to lunisolar acceleration

• Nutations of plant organs are significantly affected by the circatidal modulation in the gravitational force exerted by the Moon and Sun (lunisolar tidal acceleration, Etide). In a previous study on nutational rotations of stem apices, we observed abrupt alterations in their direction and irregularities of the recorded trajectories. Such transitions have not yet been analysed in detail.
• Peppermint plants were continuously recorded with time‐lapse photography and aligned with contemporaneous time courses of the Etide estimates. Each nutational stem tip movement path was assigned to one of two groups, depending on its geometry, as: (i) regular elliptical movements and (ii) irregular movements (with a random type of trajectory). Analyses of the correlation between the plant nutation trajectory parameters and Etide, as well as of the trajectory geometry of the individual plants were performed.
• The trajectory geometry of young mint stem apices was related to the velocity of the apex rotation and significantly affected by the gravitational force estimated from the Etide. A low velocity of nutational movement, associated with the random character of the trajectory, usually occurred simultaneously with local minima or maxima of Etide. As the mint plant ages, the transitions in the stem tip trajectory were limited; no correspondence with Etide dynamics was observed.
• The results indicate that the plant tip geometry path transitions with respect to the changing gradient of lunisolar tidal acceleration could be interpreted as manifestation of a continuous accommodation of the shoot apical part to the state of minimum energy dissipation.

     

Whole-tree level water balance and its implications on stomatal oscillations in orange trees [Citrus sinensis (L.) Osbeck] under natural climatic conditions

Sustained cyclic oscillations in stomatal conductance, leaf water potential, and sap flow were observed in young orange trees growing under natural conditions. The oscillations had an average period of approximately 70 min. Water uptake by the roots and loss by the leaves was characterized by large time lags which led to imbalances between water supply and demand in the leaves. The bulk of the lag in response between stomatal movements and the upstream water balance resided downstream of the branch, with branch level sap flow lagging behind the stomatal conductance by approximately 20 min while the stem sap flow had a much shorter time lag of only 5 min behind the branch sap flow. This imbalance between water uptake and loss caused transient changes in internal water deficits which were closely correlated to the dynamics of the leaf water potential. The hydraulic resistance of the whole tree fluctuated throughout the day, suggesting transient changes in the efficiency of water supply to the leaves. A simple whole-tree water balance model was applied to describe the dynamics of water transport in the young orange trees, and typical values of the hydraulic parameters of the transpiration stream were estimated. In addition to the hydro-passive stomatal movements, whole-tree water balance appears to be an important factor in the generation of stomatal oscillations.     

Sperm motility characteristics of wild Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta m. trutta L.) as a basis for milt selection

The aim of the study was to determine the sperm motility parameters in wild Atlantic salmon and sea trout to define criteria important for selection of milt for controlled fertilisation. Parameters for these species were determined in the fish migrating into north‐western rivers of Poland at spawning time. Eight motility parameters percentage of motile sperm (MOT), curvilinear velocity (VCL), average path velocity (VAP), straight line velocity (VSL), linearity (LIN), straightness (STR), amplitude of lateral head displacement (ALH), beat cross frequency (BCF) and motility duration were subjected to computer‐assisted sperm analysis (CASA). Milt of most individuals studied representing both salmon and trout showed spermatozoa density of 12–22 × 10⁹ ml^?1 and a high percentage of motile sperm (>70%). In general, spermatozoa swim progressively with slightly curved trajectories (mean STR = 70%, LIN = 65%) and velocity VCL of 180 μm s^?1 (salmon) and 190 μm s^?1 (trout), at 10 s post‐activation. Such sperm is easily accessible in the wild populations of salmon and sea trout and is recommended for use in reproduction trials. The spermatozoa of sea trout seem to show a greater tendency to follow curvilinear trajectories than those of salmon, both in the beginning and the final phase of motion. In the first phase of motility, the values and time dependencies of the motility parameters were similar in both species. In the end phase of movement differences in LIN and BCF time dependencies were found in the samples representing the two species. In salmon the linearity and beat cross frequency remained stable in this phase, contrary to the patterns in sea trout for which LIN decreased while BCF increased in the end period of movement. Durations of movement were similar in both species (ranges of 20–40 s).     

Effect of environment on the adaptive abilities of fry roach Rutilus rutilus (L.) (Cyprinidae) during early ontogenesis

In recent years a considerable decrease in the abundance of predatory fishes has been observed in spawning tributaries of the Rybinsk Reservoir caused by their intensive catching. The lack of encounters with predators before the downstream migration of young fish hampers the development of necessary skills of defensive behavior in the absence of predation experience. As a result, after downstream migration, the juveniles are incapable of adapting to the predation pressure in the reservoir and are subjected to intensive elimination. The adaptive potential of the roach Rutilus rutilus L. was experimentally studied in siblings raised from the larvae to the late fry stage both in the presence and absence of a predator. It has been found that the fry that was raised under different conditions differed in their adaptive potential in new environment conditions.     

The effect of moisture stress on stolon and adventitious root development in white clover (Trifolium repens L.)

Summary Humidity, at the young nodes of white clover stolones, varied by enclosing nodes in the atmosphere above a range of saturated solutions, inhibited root initiation at 85% RH or less. The threshold humidity for root initiation increased to about 93% on young nodes subject to moisture stress or old nodes on well watered plants in which root initiation had been previously suppressed by low humidity.Roots at old nodes and at the three youngest on stolons were either subject to moisture stress or adequately watered. Growth of young roots and N₂-fixation were more adversely affected by the direct effects of drought than by subjecting old roots to drought. Although old roots under stress affected new root growth and N₂-fixation, length of roots and lateral root number were little affected. By contrast stolon growth was affected more by stress to old roots than to young nodes, although after 6 weeks the contribution made by young roots to stolon growth was almost as high as old roots.The data suggest that deep roots at old nodes will allow clover stolons to grow during drought due to the high acropetal movement of water but initiation of roots and functioning of young roots at the soil surface will be adversely affected, with possible implications on the persistence of clover.     

Net ground speed of downstream migrating radio-tagged Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) smolts in relation to environmental factors

The downstream migration of Atlantic salmon (Salmo salarL.) and sea trout smolt (S. trutta L.) was investigated using radio telemetry in the spring of 1999 and 2000. Forty wild sea trout smolts, 20 F1 sea trout smolts, 20 hatchery salmon smolts and 20 salmon smolts from river stockings were radio tagged and released in the Danish River Lilleaa. The downstream migration of the different groups of fish was monitored by manual tracking and by three automatic listening stations. The downstream migration of radio tagged smolts of both species occurred concurrently with their untagged counterparts. The diel migration pattern of the radio tagged smolts was predominantly nocturnal in both species. Wild sea trout smolt migrated significantly faster than both the F1 trout and the introduced salmon. There was no correlation between net ground speed, gill Na⁺,K⁺-ATPase activity or fish length in any of the different groups. The migration speed of wild sea trout smolts was positively correlated with water discharge in both years. In F1 sea trout smolts, migration speed was positively correlated with temperature in 1999. The migration speed of salmon smolts did not correlate to any of the investigated parameters.     

Local growth differences in perch (Perca fluviatilis L.) in a Baltic archipelago

Data on the chemical composition of the hard water rivers Rhine and Rhone, published elsewhere, are stored in a new data bank, RRQUE. In this paper the seasonal variation in pH and concentrations of calcium, bicarbonate and sulphate at 7 stations in the Rhine and 7 in the Rhone are described. The concentrations of calcium, bicarbonate and sulphate show important increases with increasing distance from the source. In both rivers acidification gradually occurs downstream and is thought to be caused by the decomposition of disposed organic matter. It is shown that the normal seasonal patterns of these 4 chemical variables are negated by anthropogenic effects.     

Transport and metabolism of labelled abscisic acid in broad-bean plants (Vicia faba L.)

The movement of 2-¹⁴C-abscisic acid applied to a mature leaf of broad-bean plants ( Vicia faba L. cv. Aguadulce) was investigated by liquid scintillation counting and autoradiography. The radioactivity was readily transported into the whole plant by the phloem after 90 min. Thereafter, radioactivity moved towards the upper part of the plant, where it accumulated in the young growing leaves and in the apical bud. During transport, 2-¹⁴C- ABA was slightly metabolized, and a subsequent rapid metabolism occurred in the young leaves of the apical part of the plant and in the axillary buds released from apical dominance in decapitated plants. Transport of exogenous ABA from the apical bud presented the characteristics of a diffusion transport.     

加速流对鲢、鳙幼鱼下行过程中游泳行为的影响

研究以具有下行洄游需求的鲢(Hypophthalmichthys molitrix)、鳙(Aristichthys nobilis)幼鱼为实验对象, 分别在2种不同流态加速流(Ⅰ: 22—55 cm/s, Ⅱ: 25—60 cm/s)中进行下行实验, 对实验鱼在2种加速流中的游泳行为(下行率、下行方式及各区域游泳时间)进行定量分析并利用游泳停留时间百分比F_t衡量其偏好水流速度。结果显示: 加速流下鲢、鳙均表现出了直接下行与非直接下行两种行为。其中加速流Ⅰ中鲢、鳙直接下行率分别为35.71%、30.00%, Ⅱ中分别为45.83%、59.09%。非直接下行的鲢在2种加速流中小于30 cm/s流速区域的停留时间显著高于其他区域(P<0.05), 即鲢在实验条件下的偏好水流速度范围为小于30 cm/s; 非直接下行的鳙在加速流Ⅰ中小于30 cm/s及50—55 cm/s流速区域的停留时间显著高于其他区域(P<0.05), Ⅱ中小于30 cm/s流速区域的停留时间显著高于其他区域(P<0.05), 即鳙本实验条件下偏好水流速度范围为小于30 cm/s。将2种加速流流速相同区域合并分析发现鲢、鳙在小于30 cm/s和50—55 cm/s流速区域的停留时间存在显著性差异(P<0.05), 中间及高流速区域无明显性差异(P>0.1)。研究表明: 加速流对鲢、鳙下行游泳行为产生了影响且2种鱼在下行通过方式和偏好流速选择上存在一定的种间差异性。     

Key stimuli of prey for toads (Bufo bufo L.): Configuration and movement patterns

Summary The ability of the Common ToadBufo bufo (L.) to distinguish between a worm-like and an antiworm-like (e.g., a bar at right angles to its direction of motion) moving stripe is not generally altered by movement dynamics, such as velocity of motion or by particular movement patterns—so far as has been investigated. A small square stimulus, however, with its indifferent shape is more attractive as prey for the toad when displaced in a stepwise manner, rather than moved at corresponding continuous (constant) velocity. Step frequencies of 1 to 2 cps were found to have optimal releasing values.Supported by the Deutsche Forschungsgemeinschaft Ew 7/6     

Soil water dynamics in row and interrow positions in soybean (Glycine max L.)

Quantitative knowledge of infiltration processes and the mechanisms that control water movement in soil is necessary to properly manage water and chemical use in agricultural fields. The objective of this study was to compare the soil water content dynamics in row and interrow positions in a soybean crop (Glycine max L.) under conventional (plow) tillage. Two field plots (Beltsville silt loam soil, Fine-loamy mixed mesic Typic Fragiudult) were instrumented with Time Domain Reflectometry (TDR) probes at 0–10 cm, 0–25 cm and 0–40 cm depths. TDR probes were installed in the row and interrow positions. Soil water content was continuously monitored at 1 hour intervals. The distribution of infiltrated water and evapotranspiration showed strong row-interrow patterns. The row positions received significantly more water during precipitation than the interrow positions. Water loss, due to evapotranspiration, was also significantly greater in the row position than in the interrow position. Both plant and soil characteristics appeared to be important factors for infiltration and redistribution. The results of this study suggested that the presence of the crop canopy altered the surface boundary conditions of the soil and, hence, the volume of infiltrating water. Results of this study suggest that in order to model water movement in row crops, the ability to simulate canopy architecture and flow processes in two dimensions is necessary.