Locomotion of Gymnarchus Niloticus： Experiment and Kinematics

In addition to forward undulatory swimming, Gymnarchus niloticus can swim via undulations of the dorsal fin while the body axis remains straight; furthermore, it swims forward and backward in a similar way, which indicates that the undulation of the dorsal fin can simultaneously provide bidirectional propulsive and maneuvering forces with the help of the tail fin. A high-resolution Charge-Coupled Device （CCD） imaging camera system is used to record kinematics of steady swimming as well as maneuvering in G. niloticus. Based on experimental data, this paper discusses the kinematics （cruising speed, wave speed, cycle frequency, amplitude, lateral displacement） of forward as well as backward swimming and maneuvering. During forward swimming, the propulsive force is generated mainly by undulations of the dorsal fin while the body axis remains straight. The kinematic parameters （wave speed, wavelength, cycle frequency, amplitude） have statistically significant correlations with cruising speed. In addition, the yaw at the head is minimal during steady swimming. From experimental data, the maximal lateral displacement of head is not more than 1% of the body length, while the maximal lateral displacement of the whole body is not more than 5% of the body length. Another important feature is that G. niloticus swims backwards using an undulatory mechanism that resembles the forward undulatory swimming mechanism. In backward swimming, the increase of lateral displacement of the head is comparatively significant; the amplitude profiles of the propulsive wave along the dorsal fin are significantly different from those in forward swimming. When G. niloticus does fast maneuvering, its body is first bent into either a C shape or an S shape, then it is rapidly unwound in a travelling wave fashion. It rarely maneuvers without the help of the tail fin and body bending.     

The ontogeny of the locomotor wave in sevruga fish (Acipenser stellatus Pall.)

Continuous filming of the swimming movements of sevruga prelarvae (Acipenser stellatus Pall.) was performed over the first to the fifteenth post-hatching days. These data were used to determine three locomotor characteristics: {f(v, θ), A(v, θ), w(v, θ)} where f is the frequency of the transverse oscillations; A is the amplitude of the tail fin movements; w is the speed of the locomotor wave; v is the speed of the locomotion; and θ is the number of days during which the filming was carried out. In addition, the comparison of two characteristics was performed. These are the step length L(v, θ) and the wavelength λ(v, θ), where L ≡ vT is the distance that a fish covers in time T ≡ 1/f and λ is λ ≡ wT. The results led to the conclusion that the prelarva swimming movements achieve the carangiform mode by the end of the second week. This is characteristic of adults and coincides with the beginning of external feeding. The mode is represented by an equation that follows from the generalized Bainbridge’s law: f = f ₀ + f ₁ v/H. The equation includes one anatomical parameter H of total length and two kinematic parameters f ₀ and f ₁, which can be calculated by the linear approximation method. These are the kinematic parameters that are changed in the early ontogenesis when 1 ≤ θ ≤ 15. However, the parameters become stable when θ ≥ 15. This means that the parameter values are constant and similar to those of adult fish. The similar properties of stabilization and variability have the kinematic parameters of other locomotor characteristics.

     

Disturbance and the structure of coral reef fish communities on the reef slope

Three levels of physical disturbance were applied to corals in permanent 10x10 m quadrats along a section of fringing reef at Lizard Island on the Great Barrier Reef to investigate the response of fish assemblages. Tabular and corymbose corals were overturned and left in situ, reducing total hard coral cover from ˜55% to ˜47%, ˜43%, and ˜34%. Despite pre-existing associations with benthic cover, all fish groups examined (pomacentrids, labrids, chaetodontids, and acanthurids) were resistent to benthic disturbances at the level and scale at which they were applied. Partial Mantel's tests, in combination with partial Canonical Correspondence Analysis enabled spatial and temporal variation to be factored out from experimental effects. Most of the variation in the fish community could be assigned to spatio-temporal variables, indicating that spatial structure over the reef landscape may moderate localised disturbance effects. This study indicates that coral reef fish assemblages may be more resistant to disturbance than many correlative studies would suggest, and highlights a need for further information on levels and scales of natural habitat disturbance in order to apply a structured approach to the experimental investigation of the importance of habitat in structuring coral-reef fish assemblages.     

Optimal shape and motion of undulatory swimming organisms

Undulatory swimming animals exhibit diverse ranges of body shapes and motion patterns and are often considered as having superior locomotory performance. The extent to which morphological traits of swimming animals have evolved owing to primarily locomotion considerations is, however, not clear. To shed some light on that question, we present here the optimal shape and motion of undulatory swimming organisms obtained by optimizing locomotive performance measures within the framework of a combined hydrodynamical, structural and novel muscular model. We develop a muscular model for periodic muscle contraction which provides relevant kinematic and energetic quantities required to describe swimming. Using an evolutionary algorithm, we performed a multi-objective optimization for achieving maximum sustained swimming speed U and minimum cost of transport (COT)--two conflicting locomotive performance measures that have been conjectured as likely to increase fitness for survival. Starting from an initial population of random characteristics, our results show that, for a range of size scales, fish-like body shapes and motion indeed emerge when U and COT are optimized. Inherent boundary-layer-dependent allometric scaling between body mass and kinematic and energetic quantities of the optimal populations is observed. The trade-off between U and COT affects the geometry, kinematics and energetics of swimming organisms. Our results are corroborated by empirical data from swimming animals over nine orders of magnitude in size, supporting the notion that optimizing U and COT could be the driving force of evolution in many species.     

An Ecological Risk Assessment of Formaldehyde

A multi-tiered environmental risk assessment of formaldehyde determined the possibility of harmful effects on organisms in certain environmental compartments in Canada. A review of the relevant information indicates that biota are exposed to formaldehyde primarily in air and, to a lesser extent, in water. Worst-case scenarios predict that the estimated exposure values likely to be encountered in Canada for water and air are not expected to exceed estimated no-effects values. Therefore, the environmental risks associated with concentrations of formaldehyde likely to be found in Canada are low.     

Volumetric imaging of fish locomotion

Fishes use multiple flexible fins in order to move and maintain stability in a complex fluid environment. We used a new approach, a volumetric velocimetry imaging system, to provide the first instantaneous three-dimensional views of wake structures as they are produced by freely swimming fishes. This new technology allowed us to demonstrate conclusively the linked ring vortex wake pattern that is produced by the symmetrical (homocercal) tail of fishes, and to visualize for the first time the three-dimensional vortex wake interaction between the dorsal and anal fins and the tail. We found that the dorsal and anal fin wakes were rapidly (within one tail beat) assimilated into the caudal fin vortex wake. These results show that volumetric imaging of biologically generated flow patterns can reveal new features of locomotor dynamics, and provides an avenue for future investigations of the diversity of fish swimming patterns and their hydrodynamic consequences.     

Studies on the proteolytic enzymes of invertebrates constituting fish food

Studies were carried out on the proteolytic activity of trypsin and pepsin-like enzymes of invertebrates consituting fish food. Relations between proteolytic activity of enzymes, pH, and temperature were established.     

Ecotoxicological studies with the freshwater rotifer Brachionus calyciflorus

The use of the freshwater rotifer Brachionus calyciflorus as a test organism for ecotoxicological studies was examined. Changes in the feeding-, swimming behavior- and demographic characteristics of the rotifers exposed to increasing concentrations of copper (Cu) were studied and the relationships between the different test parameters and their ecological relevance evaluated.Relatively simple short-term bioassay methods were developed to measure the swimming activity (2 hours) and the filtration (5 hours) rate. Life-table experiments were performed to asses the long-term effects of Cu on the rotifers. Significant reductions in the filtration rate, the swimming activity and the demographic parameter r were observed at 20, 12 and 5 g 1^–1 of Cu, respectively. The implications and the possible ecotoxicological applications of the results are discussed.     

Effects of temperature on larval fish swimming performance: the importance of physics to physiology

Temperature influences both the physiology offish larvae and the physics of the flow conditions under which they swim. For small larvae in low Reynolds number (Re) hydrodynamic environments dominated by frictional drag, temperature‐induced changes in the physics of water flow have the greatest effect on swimming performance. For larger larvae, in higher Re environments, temperature‐induced changes in physiology become more important as larvae swim faster and changes in swimming patterns and mechanics occur. Physiological rates at different temperatures have been quantified using Q₁₀s with the assumption that temperature only affected physiological variables. Consequently, Q₁₀s that did not consider temperature‐induced changes in viscosity overestimated the effect of temperature on physiology by 58% and 56% in cold‐water herring and cod larvae respectively. In contrast, in warm‐water Danube bleak larvae, Q₁₀s overestimated temperature‐induced effects on physiology by only 5–7%. This may be because in warm water, temperature‐induced changes affect viscosity to a smaller degree than in cold water. Temperature also affects muscle contractility and efficiency and at high swimming velocities, efficiency decreases more rapidly in cold‐exposed than in warm‐exposed muscle fibres. Further experiments are needed to determine whether temperature acts differently on swimming metabolism in different thermal environments. While hydrodynamic factors appear to be very important to larval fish swimming performance in cold water, they appear to lose importance in warm water where temperature effects on physiology dominate. This may suggest that major differences exist among locomotory capacities of larval fish that inhabit cold, temperate waters compared to those that live in warm tropical waters. It is possible that fish larvae may have developed strategies that affect dispersal and recruitment in different aquatic habitats in order to cope not only with temperature‐induced physiological challenges, but physical challenges as well.     

Mesozoic plate tectonic reconstruction of the Carpathian region

Palaeomagnetic, palaeobiogeographic and structural comparisons of different parts of the Alpine-Carpathian region suggest that four terranes comprise this area: the Alcapa, Tisza, Dacia and Adria terranes. These terranes are composed of different Mesozoic continental and oceanic fragments that were each assembled during a complex Late Jurassic-Cretaceous-Palaeogene history. Palaeomagnetic and tectonic data suggest that the Carpathians are built up by two major oroclinal bends. The Alcapa bend has the Meliata oceanic unit, correlated with the Dinaric Vardar ophiolite, in its core. It is composed of the Western Carpathians, Eastern Alps and Southern Alcapa units (Transdanubian Range, Bükk). This terrane finds its continuation in the High Karst margin of the Dinarides. Further elements of the Alcapa terrane are thought to be derived from collided microcontinents: Czorsztyn in the N and a carbonate unit (Tisza?) in the SE. The Tisza-Dacia bend has the Vardar oceanic unit in its core. It is composed of the Bihor and Getic microcontinents. This terrane finds its continuation in the Serbo-Macedonian Massif of the Balkans.The Bihor-Getic microcontinent originally laid east of the Western Carpathians and filled the present Carpathian embayment in the Late Palaeozoic-Early Mesozoic. The Vardar ocean occupied an intermediate position between the Western Carpathian-Austroalpine-Transdanubian-High Karst margin and the Bihor-Getic-Serbo-Macedonian microcontinent. The Vardar and Pindos oceans were opened in the heart of the Mediterranean-Adriatic microcontinent in the Late Permian-Middle Triassic. Vardar subducted by the end of Jurassic, causing the Bihor-Getic-Serbo-Macedonian microcontinent to collide with the internal Dinaric-Western Carpathian margin.An external Penninic-Váhic ocean tract began opening in the Early Jurassic, separating the Austroalpine-Western Carpathian microcontinent (and its fauna) from the European shelf. Further east, the Severin-Ceahlau-Magura also began opening in the Early Jurassic, but final separation of the Bihor-Getic ribbon (and its fauna) from the European shelf did not take place until the late Middle Jurassic.The Alcapa and the Tisza-Dacia were bending during the Albian-Maastrichtian. The two oroclinal bends were finally opposed and pushed into the gates of the Carpathian embayment during the Palaeogene and Neogene. At that time, the main N-S shortening in distant Alpine and Hellenic sectors was linked by a broader right-lateral shear zone along the former Vardar suture.     

长江天鹅洲故道和老河故道水生生物多样性的比较研究

本文报道了长江中游开敞式天鹅洲故道和封闭式老河故道浮游植物、浮游动物、底栖动物及水生维管束植物四大类水生生物多样性的异同和变化。浮游植物、浮游动物和水生维管束植物的多样性都是老河故道高于天鹅洲故道,底栖动物的多样性则是天鹅洲故道高于老河故道。预期随着天鹅洲故道由开敞式向封闭式的演变,其水生生物的多样性也将不断增大     

Effects of waves on the early growth of Vallisneria americana

1. The impacts of 0.15-m waves on the survival and short-term growth and development of young Vallisneria americana plants were studied in experimental raceways. Young plants were planted at three depths within both wave and control raceways. Wave events were designed to simulate wave disturbances caused by boat traffic and were generated five or six times each day during the 67-day experimental growth period. The 0.15-m waves generated produced a maximum shear velocity of about 1.4 m s⁻¹ as they swept over the plants. 2. All plants survived at all depths in both treatments. However, plants exposed to the waves accumulated significantly less total mass than controls. The total mass accumulation of wave-exposed plants was only 50% of that of undisturbed plants. In addition, the plants experiencing the waves had significantly shorter leaves and produced significantly fewer daughter plants. 3. While plants under both wave and no wave treatments had a similar relative growth rate and both showed a net positive growth over the experimental period, those exposed to frequent wave energy developed more slowly due to continuous leaf loss caused by the waves. Plants exposed to even modest wave energy may spread more slowly and be less resilient to recovery from other forms of disturbance.     

Frenetic activation of fish spermatozoa flagella entails short-term motility, portending their precocious decadence

In most species, fish spermatozoa activate their motility on contact with the external medium (sea or fresh water depending of their reproductive habitat). Their flagella immediately develop waves propagated at high beat frequency (up to 70 beats s⁻¹), which propel these sperm cells at high velocity (6–10 mm min⁻¹), but for a quite short period of time, usually limited to minutes. Their specific inability to restore their energy content (mostly adenosine triphosphate) fast enough relatively to their high rate of energy consumption by flagellar contributes mainly to the activity arrest of motility, as the spermatozoa need to rely on early accumulated energy prior to activation. This review of the published data explains the present understanding of physico-chemical mechanisms by which flagellar motility is activated (mostly through osmotic and ionic regulation) and then propels sperm cells at speed. It aims also to describe the gradual arrest of their motility much of which occurs within a few minutes.     

The contribution of setal blades to effective swimming in the aquatic mite Limnochares americana (Acari: Prostigmata: Limnocharidae)

Two rows (anterior and posterior) of long fine setae inserted on the 3rd, 4th and 5th segments of the last two pairs of legs of L. americana form functional swimming blades. Each swimming setal is mounted in a mobile basal socket, and the structure of the setal base and socket configuration ensure that the blades will be passively erected during the leg's power stroke to provide increased thrust and collapsed during the recovery stroke to reduce water resistance. The erect swimming blades increase the effective area for thrust by approximately 500%, making it possible for the mite to lift itself off the bottom. The IVth legs contribute the greater proportion of the thrust developed during paddling, and the 4th segment (genu) bears the largest swimming blades on both legs.     

Drag reduction of fish skin mucus: Relationship to mode of swimming and size

Drag reduction by skin mucus was measured from Gulf of Eilat fish. Activity of burst swimmers was greater than manoeuvre swimming fish. Large fish from the same species had higher mucus drag reducing activity than smaller specimens.     

Further comment on drag and reconfiguration of macrophytes

1. The paper by Sand‐Jensen (2003 , Freshwater Biology, 48 , 271), and the subsequent comment and reply ( Sukhodolov, 2005 , Freshwater Biology, 50 , 194; Sand‐Jensen, 2005 , Freshwater Biology, 50 , 196), are discussed. I present partial theory describing how the macrophyte bending angle changes with increased flow velocity, demonstrating a nonlinear relation. 2. While Sand‐Jensen (2005) is correct that plant wetted area is the only characteristic area that can be measured easily, some other measure of the exposure area of the plant stand to the flow may be preferable. The relationship in Sand‐Jensen (2003) between the dimensionless drag coefficient and flow velocity depends on the definition of characteristic area. Hence, the analysis involving the drag parameter in Sand‐Jensen (2003) should be interpreted with care.     

An Ecological Risk Assessment of Air Emissions of Trace Metals from Copper and Zinc Production Facilities

Trace metals are components of releases to air emitted by copper and zinc production facilities in Canada. Six metals (copper, zinc, nickel, lead, cadmium, and arsenic) are examined as part of an overall environmental assessment of these releases. Estimates of metal deposition rates to soils and surface waters were derived from monitoring data in the vicinity of the production facilities and also through dispersion modelling studies. Fate and transport modelling of the metals deposited allowed an estimation of critical loads. Estimated annual deposition rates were compared with 25^th-percentile critical loads typically representative of effects on sensitive organisms under 25% of conditions in sandy soils or circumneutral to acidic lake waters. The results of the comparison suggest that there is a potential for adverse effects on aquatic and/or soil-dwelling organisms from exposure to steadystate concentrations of metals in the vicinity of copper and zinc production facilities. Approaches of particular significance in these assessments include probabilistic estimation of critical loads for metals, allowance for the speciation of metals defining the bioavailable fraction and limiting critical effect levels to the high end of natural background metal concentrations.