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.     

Swimming performance and metabolism of 0+ year Thymallus arcticus

The prolonged swimming speed and metabolic rate of 0+ year Arctic grayling Thymallus articus were examined with respect to current velocity, water temperature and fish size, and compared to conditions fish occupy in the river. Oxygen consumption (mg O₂ h⁻¹) increased with fish mass and temperature (6–23° C), with a steep increase in metabolic rate between 12 and 16° C. Absolute prolonged swimming speed (cm s⁻¹) increased rapidly with fish size (total length, L _T, and mass), however, fish in the natural stream habitat occupied current velocities between 15 and 25 cm s⁻¹ or 4  L _T s⁻¹, approximately half their potential prolonged swimming speed (10  L _T s⁻¹).     

An application of the plaster dissolution method for quantifying water velocity in the shallow hyporheic zone of an Appalachian stream system

1. A method for quantifying interstitial water velocity based on the dissolution rate of plaster of Paris standards was developed as part of a study of vertical, longitudinal (1–4 order sites) and seasonal variation in the biotic and physical characteristics of the shallow hyporheic zone (0–30 cm) of a headwater stream system in West Virginia, U.S.A.
2. A calibration model was developed using a water velocity simulation tank to relate mass loss of plaster standards to water velocity and temperature. The model was then used to calculate water velocity through artificial substrata embedded in the shallow hyporheic zone of four stream reaches based on in situ mass loss of plaster standards.
3. Water velocity in the hyporheic zone increased with stream order, was highest in early spring and winter during high stream base flows, and decreased with depth into the substratum. There was a strong interaction between depth and season: during periods of high stream discharge, water velocity through the upper level of the shallow hyporheic zone (0–10 cm into the substrate) increased disproportionately more than velocity at greater depths. Mean interstitial velocity in March ranged from 0 cm s^–1 in the lowest level (20–30 cm) to 3.5 cm s^–1 at the upper level (0–10 cm) at the first‐order site, and from 2.5 cm s^–1 (20–30 cm) to 9.5 cm s^–1 (0–10 cm s^–1) at the fourth‐order site. Gradients in stream discharge and sediment permeability accounted for treatment effects.
4. Use of calibrated data improved the ability to resolve among‐season differences in interstitial water movement over the use of uncalibrated mass loss data. For some applications of the plaster standard method, empirical calibration may not be necessary.     

Micro-environmental characteristics of filamentous algal communities in flowing freshwaters

SUMMARY. 1. Filamentous algae in flowing freshwaters can represent a spatially and temporally distinct sub-habitat for epiphytic diatom communities. This sub-habitat is described in a low discharge, spring-fed stream with extensive filamentous green algal mats, and in a tuft of Cladophora glomerata (L.) Kützing from a large river.
2. Oxygen micro-electrodes, a thermistor current velocity probe, a standard pH probe and water chemistry were employed to assess spatial heterogeneity. Temporal patterns of epiphyte colonization were evaluated on filamentous artificial substrates.
3. There were steep spatial gradients in the low discharge stream. At mid-day, O₂ ranged from 0–1.5 times air-saturated O₂ concentrations, pH varied from 7.25–8.0, and current velocity spanned 0–0.5 m s⁻¹. Areas near the surface of algal mats had high O₂, pH and current velocity. These patterns were correlated with epiphyte community structure.
4. In the interior of C. glomerata tufts O₂ concentration was raised and current velocity depressed compared to the surrounding water, even when external current velocity was as high as 0.4 m s⁻¹.
5. After thirty-five days of colonization of artificial substrate in the low discharge environment, epiphyte communities were similar to those on filamentous atgae. Epiphyte diversity on artificial substrates subsequently decreased compared to natural substrates as did the similarity between the types on substrates, suggesting that microscale renewal of epiphyte habitat (growth of filamentous algae) maintains high epiphytic diversity.     

Behaviour and performance of juvenile shortnose sturgeon Acipenser brevirostrum at different water velocities

Critical swimming speeds (mean ± s . e .) for juvenile shortnose sturgeon Acipenser brevirostrum were 34·4 cm s⁻¹± 1·7 (2·18 ± 0·09 body lengths, BL s⁻¹). Swimming challenges at 10, 20 and 30 cm s⁻¹ revealed that juvenile A. brevirostrum are relatively poor swimmers, and that the fish did not significantly modify their swimming behaviour, although they spent more time substratum skimming ( i.e. contact with flume floor) at 30 cm s⁻¹ relative to 10 cm s⁻¹. When present, these behavioural responses are probably related to morphological features, such as flattened rostrum, large pectoral fins, flattened body shape and heterocercal tail, and may be important to reduce the costs of swimming.     

Resistance of a cased caddis larva to accidental entry into the drift: the contribution of active and passive elements

SUMMARY. . 1. The resistance to passive entry into the drift of first to fifth instar larvae of Allogamus auricollis (Pictet, 1834), a case-bearing caddis-fly, was investigated in the laboratory using an artifical stream channel.
2. Dead larvae in their cases were exposed to different current speeds. When the heads of the larvae were directed towards the water flow (frontal position), the current necessary to wash larvae away ranged from 3 cm s^-l (first instars) to 21 cm s^-1 for fifth instars. When the larvae were at right angles to the current (lateral position), these speeds were 2 and 9cm s^-1, respectively. In terms of force (Newtons), this passive resistance to drift ranged from 0.3x10^-6 N (first instar, frontal position) to 307.0x10^-6 N (fifth instar, frontal position). The data obtained in the experiments were in good agreement with values calculated from hydrodynamic equations, using biometric parameters of the larvae.
3. Total resistance to drift was studied by exposing living larvae to different current speeds. The speed just sufficient to wash larvae away ranged from 13 cm s^-1 in the first instar to 27.9 cm s^-1 in the fifth instar (frontal position). In terms of force, the total resistance to drift varied between 5.3x10^-6 N (first instar) and 547.5x10^-6 N (last instar).
4. The difference between total and passive resistance to drift was defined as'active resistance to drift', and is due to the effectiveness of a larva's attachment to the substrate. It ranged from 3.5x10^-6 N (first instar) to 222.8X 10^-6 N (last instar).     

Swimming performance of European eel (Anguilla anguilla (L.)) elvers

To determine the relation between swimming endurance time and burst swimming speed, elvers of the European eel, Anguilla anguilla (L.), were made to swim at speeds from 3.6 to 7.2 L (body lengths) s⁻¹ in both fresh and sea water. Swimming endurance time of elvers averaging 7.2 cm total length decreased logarithmically with increased swimming speed from 3.0 min at 3.5 L s⁻¹ to 0.7 min at 5.0 L s⁻¹, and again logarithmically but with a lesser slope to 0.27 min at 7.5 L s⁻¹. No differences were found between fresh and sea water elvers. In still water, elvers could swim at high speeds for about 10–45m before exhaustion, depending upon speed. Elvers would be able to make virtually no progress against water currents >50 cm s⁻¹. Drift in coastal water currents and selective tidal transport probably involve swimming speeds below those tested in this study. Migration into freshwater streams undoubtedly involves avoidance of free stream speeds and a combination of burst and sustained swimming.     

Hydroacoustic measurement of swimming speed of North Sea saithe in the field

Saithe Pollachius virens , tracked diurnally with a split-beam echosounder, showed no relationship between size and swimming speed. The average and the median swimming speeds were 1·05 m s⁻¹(±0·09 m s⁻¹) and 0·93 m s⁻¹, respectively. However, ping-to-ping speeds up to 3·34 m s⁻¹ were measured for 25–29 cm fish, whose swimming speeds were significantly higher at night (1·08 m s⁻¹) than during the day (0·72 m s⁻¹). The high average swimming speed could be related to the foraging or streaming part of the population and not to potential weakness of the methodology. However, the uncertainty of target location increased with depth and resulted in calculated average swimming speeds of 0·15 m s⁻¹ even for a stationary target. With increasing swimming speed the average error decreased to 0 m s⁻¹ for speeds >0·34 m s⁻¹. Species identity was verified by trawling in a pelagic layer and on the bottom.     

Phenology of Sirodotia suecica (Batrachospermaceae, Rhodophyta) in a high-altitude stream in central Mexico

The morphology and phenology of a monoecious population of Sirodotia suecica Kylin was evaluated seasonally in a central Mexican fifth-order high-altitude stream. Abundance of gametophytes is positively correlated with concentrations of total dissolved solids, specific conductivity and total ionic concentration; being present the whole dry season and disappearing in the rainy season. The gametophytes grew in eutrophic circumstances and particular microhabitat conditions: high current velocity (66–122 cm s⁻¹), low irradiance (75–263 µmol photons m⁻² s⁻¹) and shallow depth (7–26 cm). Percent cover of gametophytes ranged from 5–90% and significant differences in abundance were not observed when alga was present. Some morphological and reproductive characteristics seem to be adaptations to high current velocity: abundant secondary branches, spermatangia and carpogonia. 'Chantransia' stage, microscopic creeping filaments associated with the base of the gametophyte, were not observed in natural conditions. In terms of reproductive success, the population studied can be regarded as highly efficient, considering the high fertilized carpogonia rate, similar to monoecious populations in lotic habitats. However S. suecica was not common in the study region because it was restricted to particular microhabitat conditions.     

The swimming abilities of recently settled post-larvae of Sillaginodes punctata

Sixty-four post-larvae of the King George whiting Sillaginodes punctata were tested in swimming chambers, against one of five flow-through velocities (2, 4, 6, 8 or 10 cm s ⁻¹) for up to a maximum of 120 min. Fish were determined by regression to have an FV₅₀ (50% fatigue velocity) of 6.0 cm s⁻¹. No fish survived the full 120 min at 10 cm s⁻¹. Sixteen individuals were tested in a swimming chamber against a flow-through velocity of 6 cm s ⁻¹ and allowed to swim to exhaustion. Fish swam between 25 and 538 min with a peak at c . 6–8 h. Total swimming time was not correlated with standard length of fish although the size range examined was narrow. Relative to recent studies on the swimming abilities of late-stage larvae of reef fishes, this study indicates that post-larval King George whiting are weak swimmers. The weak swimming ability of post-larval King George whiting is consistent with studies showing passive dispersal and recruitment of this species.     

Characteristics of dispersal in the eastern mosquitofish Gambusia holbrooki

The demographic and genetic characteristics of dispersing Gambusia holbrooki were examined relative to changes in stream flow velocity, flow direction, and rapid saltwater inundation. Dispersal of all G. holbrooki sex classes decreased as flow velocity increased, dispersal for a given flow velocity being greater in female, than male and juvenile fish respectively. Juveniles and males dispersed at low (9 mm s⁻¹) but not high (109 mm s ¹) flow. Females dispersed at both flow rates. Dispersing adults were not larger than non-dispersing adults of the same sex. Direction of dispersal was sex and size dependent, but independent of flow velocity. Larger females (>22 mm) moved preferentially downstream, while smaller females (17–22 mm) remained stationary or moved in the upstream direction. Males dispersed equally in both directions. No relationship was found between dispersal characteristics and the presence of high salt concentrations. Movement patterns at high flow were independent of glucose-6-phosphate isomerase ( GPI-2* ) alleles carried by dispersing individuals. Significant non-random dispersal of sex or size cohorts, and the interaction of dispersal with flow velocity have significant implications for the maintenance of genetic diversity in stream ecosystems, particularly where localized selection or genetic drift may alter the genetic constitution of specific sex or size cohorts. The applicability of these results to field populations is discussed.     

High- and Low-Affinity Transport of D-Glucose from Blood to Brain

Abstract: Measurements of the unidirectional blood-brain glucose flux in rat were incompatible with a single set of kinetic constants for transendothelial transport. At least two transfer mechanisms were present: a high-affinity, low-capacity system, and a low-affinity, high-capacity system. The low-affinity system did not represent passive diffusion because it distinguished between D-and L-glucose. The T_max and K _m, for the high-affinity system were 0.16 mmol 100 g⁻¹ min⁻¹ and 1 mM; for the low-affinity system, ∼ 5 mmol 100 g⁻¹ min⁻¹ and ∼ 1 M. With these values, physiological glucose concentrations were not sufficient to saturate the low-affinity system. In normoglycemia, therefore, three independent pathways of glucose transport from blood to brain appear to exist: a high-affinity facilitated diffusion pathway of apparent permeability 235·10⁻⁷ cm s⁻¹, a specific but nonsaturable diffusion pathway of permeability 85·10⁻⁷ cm s^−l, and a nonspecifc passive diffusion pathway of permeability 2·10⁻⁷ cm s⁻¹.     

Dispersion and spatial orientation of Gerris remigis in response to water current: a comparison of pre- and post-diapause adults

ABSTRACT. The movements and orientation of adult Gerris remigis Say (Hemiptera; Gerridae) were examined in an artificial stream to determine the mechanisms by which these stream-dwelling waterstriders compensate for and/or avoid downstream drift, and to compare the movement tendency of pre- and post-diapause adults. G. remigis respond to current by turning to face directly into the current (rotational orientation), intermittently rowing against the current (translational orientation), and moving onto land to avoid the current. These rotational and translational responses enable G. remigis to maintain their positions in currents =S10 cm s^-1. However, avoidance increases with current speed, and few animals are found where currents exceed 10 cm s^-1. These observations correlate well with the observed distribution of adult G. remigis in a natural stream.
Comparisons between life stages reveal that post-diapause adults move more, and are more susceptible to drift than pre-diapause adults. Post-diapause adults also avoid even slight currents (<5 cm s^_1) by seeking land, while pre-diapause adults do not show a significant preference for land until currents exceed 10 cm s^-1. These data suggest that previously reported differences in the movement tendency of pre- and post-diapause adults in the field may reflect physiologically-based behavioural differences between these two life stages rather than merely direct responses to environmental cues.     

Migrational swimming speeds of the American shad, Alosa sapidissima, in the Connecticut River, Massachusetts, U.S.A.

Of 91 sonic-tagged American shad, 78 were tracked upriver to their spawning grounds. The remaining 13 tagged shad dropped back downstream over a dam or moved downstream through the adjacent canal system. Sonic-tagged shad swam upstream individually. 'Apparent' swimming speeds (the time to travel between two points) during daylight hours ranged from 11 to 93 cm s⁻¹ when water temperatures were below 20°C and from 9.8 to 64 cm s⁻¹ when water temperatures exceeded 20°C. Swimming speeds at night ranged from 8 to 53 cm s⁻¹. As the flow rate increased, shad swam faster. A major flood, producing flows reaching 300 cm s⁻¹, flushed all sonic-tagged shad away.     

Hydraulic microdistribution patterns of larval fire salamanders (Salamandra salamandra salamandra) in the Weidlingbach near Vienna, Austria

1. This study examined the longitudinal distribution of larval fire salamanders ( Salamandra salamandra salamandra L.) in the Weidlingbach system, a first- to fourth-order tributary of the Danube near Vienna, Austria. On the microhabitat scale, actual current velocities, Reynolds numbers and Froude numbers at larval locations were measured and larval positions mapped.
2. Larval densities were highest in shallow first- and second-order tributaries where mean current speeds were less than 20 cm s⁻¹, mean Reynolds numbers were less than 12 000 and mean Froude numbers were less than 0.30. Young larvae appeared on 26 April, fully grown larvae were observed from 11 May and larvae started metamorphosis from 27 June. Young adults left the brook between 26 August and 8 September. A severe flood on 25 May significantly reduced larval density, especially at sites near the source.
3. At a given sampling station young larvae favoured microhabitats exposed to only minor hydraulic stress. As larvae grew, they also colonized microhabitats with moderate current velocity (4–15 cm s⁻¹). At sites with generally low discharge, larvae were distributed over a wider range of current velocities than at sites with higher discharge; at the latter, larvae were constricted to sheltered microhabitats.     

Is tilting behaviour at low swimming speeds unique to negatively buoyant fish? Observations on steelhead trout,Oncorhynchus mykiss,and bluegill,Lepomis macrochirus

When swimming at low speeds, steelhead trout and bluegill sunfish tilted the body at an angle to the mean swimming direction. Trout swam using continuous body/caudal fin undulation, with a positive (head-up) tilt angle ( 0 , degrees) that decreased with swimming speed ( u , cm s⁻¹) according to: 0 =(164±96).u^{(−1.14±0.41)} (regression coefficients; mean±2 s.e. ). Bluegill swimming gaits were more diverse and negative (head down) tilt angles were usual. Tilt angle was −3·0 ± 0.9° in pectoral fin swimming at speeds of approximately 0.2–1.7 body length s⁻¹ (Ls⁻¹; 3–24 cm s⁻¹), −4.5 ±2.6° during pectoral fin plus body/caudal fin swimming at 1·2–1·7 L s⁻¹ (17–24cm s⁻¹), and −5.0± 1.0° during continuous body/caudal fin swimming at 1.6 and 2.5 L s⁻¹ (22 and 35cm s⁻¹). At higher speeds, bluegill used burst-and-coast swimming for which the tilt angle was 0.1±0.6°. These observations suggest that tilting is a general phenomenon of low speed swimming at which stabilizers lose their effectiveness. Tilting is interpreted as an active compensatory mechanism associated with increased drag and concomitant increased propulsor velocities to provide better stabilizing forces. Increased drag associated with trimming also explains the well-known observation that the relationship between tail-beat frequency and swimming speed does not pass through the origin. Energy dissipated because of the drag increases at low swimming speeds is presumably smaller than that which would occur with unstable swimming.     

Seasonal dynamics of invertebrate drift in a Hong Kong stream

Drift samples were taken with paired nets on 19 occasions over a 12-month period in Tai Po Kau Forest Stream (TPKFS), Hong Kong. Mean drift density (±1 S.E.) was 277·9 ± 25·0 individuals 100 m^-3; peaks in density were apparent during autumn and spring. One hundred and two taxa were recovered from the drift, and the total number of taxa drifting was positively related to water temperatures. Over 99% of the aquatic animals collected in drift samples were insects, 10 taxa of which constituted 67·3% of the entire catch. Baetid mayflies dominated the composition of the drift, comprising 40·4% of individuals caught.
Seasonal changes in the drift of individual taxa were evident, reflecting significant relationships between drift densities and water temperature: Simulium T₁ (Diptera). Anisocentropus maculatus (Trichoptera) and Amphinemura chui (Plecoptera) drifted most in winter, whereas Chimarra T₁, Polymorphanisus astictus (Trichoptera), Helodes #1 and cf. Rhantus sp. (Coleoptera) were most numerous in summer. Drifting mayflies showed spring ( Indobaetis sp., Cinygmina T₁, Serratella T₂), autumn ( Baetiella sp., Pseudocloeon T₂), or spring and autumn ( Baetis nr pseudofrequentus ) peaks which were not clearly related to water temperature. In only two cases ( A. maculatus and P. astictus ) was TPKFS drift seasonality associated with life-cycle events. Overall, there was no evidence of community-level trends in the periodicity of stream drift in this seasonal tropical habitat.     

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.     

Sperm structure and motility of the freshwater teleost Cottus gobio

When motility of spermatozoa of Cottos gobio was initiated with distilled water, the motility rate decreased to 0% within 1 min, and significant signs of osmotic alterations were observed at the end of the motility period. By contrast, in 50 mmol 1⁻¹ NaCl solution, the motility rate persisted for 120–140 min. In both distilled water and in 50 mmol 1⁻¹ NaCl solution, the main swimming type of spermatozoa was linear motion during the whole motility period. The initial swimming velocity (50.0 ± 2.1 μm s⁻¹) measured 10 s after motility initiation was similar in both distilled water and in 50 mmol 1⁻¹ NaCl solution. In distilled water, the velocity decreased to <20 μm s⁻¹ (locally motile) during the first minute of the motility phase. In 50 mmol 1⁻¹ NaCl solutions, it remained at a constant level during the first 60 min of the motility period, but then started to decrease to <20 μm s⁻¹ after 120 min. When 5 mmol 1⁻¹ potassium cyanide, antimycin or atractyloside was added to the 50 mmol 1⁻¹ NaCl solution, the motility period was reduced to ≤2min. Ten millimoles per litre 2-deoxy-D-glucose, malonate or a mixture of 5 mmol 1⁻¹ atractyloside and 5 mmol 1⁻¹ carnithine did not effect the duration of the motility period. This indicates that sperm energy metabolism depends mainly on respiration rate and fatty acid metabolism.     

Spectacular abundance of ciliates in anoxic pond water: contribution of symbiont photosynthesis to host respiratory oxygen requirements

Abstract: Very large numbers (3466 ml⁻¹) of ciliated protozoa were found living beneath the oxic-anoxic boundary in a stratified freshwater pond. Most ciliates (96%) contained symbiotic algae ( Chlorella spp.). Peak abundance was in anoxic water with almost 1 mol free CO₂ m⁻³ and a midday irradiance of 6 μmol photon m⁻² s⁻¹. Photosynthetic rate measurements of metalimnetic water indicated a light compensation point of 1.7 μmol photon m⁻² s⁻¹ which represents 0.6% of sub-surface light. We calculate that photosynthetic evolution of O₂ by symbionts is sufficient to meet the demand of the host ciliates for 13 to 14 hours each day. Each 'photosynthetic ciliate' may therefore become an aerobic island surrounded by anoxic water.