Swimming performance of juvenile white sturgeon (Acipenser transmontanus): training and the probability of entrainment due to dredging

White sturgeon, Acipenser transmontanus (Richardson), are at risk of entrainment from dredging, with young-of-the-year fish at greatest risk. To evaluate this entrainment risk, swimming performance trials were conducted in a laboratory swim tunnel with hatchery-reared juvenile white sturgeon with varying experience levels including: naïve (only tested once), tested (re-tested after being kept in no flow) and trained (re-tested after kept in flow for nearly three weeks). Individuals of various sizes (80–100 mm TL) and all experience levels were strongly rheotactic (> 80%), but endurance was highly variable among fish. Small juveniles [< 82 mm total length (TL)] had lower escape speeds (< 40 cm s⁻¹) than medium (82–92 mm TL) and large (> 93 mm TL) naïve fish (42–45 cm s⁻¹), all of which had lower escape speeds than trained fish (72 cm s⁻¹). Behavior was also highly variable among fish. Overall, benthic station-holding behaviors were least frequent in small fish, intermediate in medium and large fish, and most frequent in trained large fish. Probability of entrainment of juvenile white sturgeon can be reduced by maintaining dredge head flow fields at less than 45 cm s⁻¹ for wild-spawned fish or by rearing hatchery fish to > 93 mm TL and exposing the fish to moderate flow velocities (10–12 cm s⁻¹) prior to their release.     

Vulnerability of age-0 pallid sturgeon Scaphirhynchus albus to fish predation

Stocking is a commonly employed conservation strategy for endangered species such as the pallid sturgeon, Scaphirhynchus albus . However, decisions about when, where and at what size pallid sturgeon should be stocked are hindered because vulnerability of pallid sturgeon to fish predation is not known. The objective of this study was to evaluate the vulnerability of age-0 pallid sturgeon to predation by two Missouri River predators under different flow regimes, and in combination with alternative prey. To document vulnerability, age-0 pallid sturgeon (<100 mm) were offered to channel catfish Ictalurus punctatus and smallmouth bass Micropterus dolomieu in laboratory experiments. Selection of pallid sturgeon by both predators was measured by offering pallid sturgeon and an alternative prey, fathead minnows Pimephales promelas, in varying prey densities. Smallmouth bass consumed more age-0 pallid sturgeon (0.95 h⁻¹) than did channel catfish (0.13 h⁻¹), and predation rates did not differ between water velocities supporting sustained (0 m s⁻¹) or prolonged swimming speeds (0.15 m s⁻¹). Neither predator positively selected pallid sturgeon when alternative prey was available. Both predator species consumed more fathead minnows than pallid sturgeon across all prey density combinations. Results indicate that the vulnerability of age-0 pallid sturgeon to predation by channel catfish and smallmouth bass is low, especially in the presence of an alternative fish prey.     

Endurance swimming of diploid and triploid Atlantic salmon

When groups of diploid (mean ±  s . e . fork length, L _F) 33·0 ± 1·4 cm and triploid (35·3 ± 0·5 cm) Atlantic salmon Salmo salar were forced to swim at controlled speeds in a carefully monitored 10 m diameter 'annular' tank no significant difference was found between the maximum sustained swimming speeds ( U _ms, maintainable for 200 min) where the fish swam at the limit of their aerobic capability. Diploids achieved 2·99 body lengths per second (bl s⁻¹)(0·96 m s⁻¹) and triploids sustained 2·91 bl s⁻¹(1·02 m s⁻¹). The selection of fish for the trials was based on their ability to swim with a moving pattern projected from a gantry rotating at the radius of the tank and the selection procedure did not prove to be significant by ploidy. A significant difference was found between the anaerobic capabilities of the fish measured as endurance times at their prolonged swimming speeds. During the course of the experimentation the voluntary swimming speed selected by the fish increased and the schooling behaviour improved. The effect of the curvature of the tank on the fish speeds was calculated (removing the curved effect of the tank increased the speed in either ploidy by 5·5%). Implications of the endurance times and speeds are discussed with reference to the aquaculture of triploid Atlantic salmon.     

The formation of migratory ripples in a mixed species bacterial biofilm growing in turbulent flow

Mixed-species biofilms, consisting of Klebsiella pneumoniae , Pseudomonas aeruginosa , Pseudomonas fluorescens and Stenotrophomonas maltophilia , were grown in glass flow cells under either laminar or turbulent flow. The biofilms grown in laminar flow consisted of roughly circular-shaped microcolonies separated by water channels. In contrast, biofilm microcolonies grown in turbulent flow were elongated in the downstream direction, forming filamentous 'streamers'. Moreover, biofilms growing in turbulent flow developed extensive patches of ripple-like structures between 9 and 13 days of growth. Using time-lapse microscopic imaging, we discovered that the biofilm ripples migrated downstream. The morphology and the migration velocity of the ripples varied with short-term changes in the bulk liquid flow velocity. The ripples had a maximum migration velocity of 800 μm h⁻¹ (2.2 × 10⁻⁷ m s⁻¹) when the liquid flow velocity was 0.5 m s⁻¹ (Reynolds number = 1800). This work challenges the commonly held assumption that biofilm structures remain at the same location on a surface until they eventually detach.     

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).     

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.     

Habitat utilization of juvenile lake sturgeon, Acipenser fulvescens, in a large Canadian river

An increased understanding of the juvenile life history stage of the lake sturgeon, Acipenser fulvescens , has been recognized as a key requirement for improving conservation efforts for this once abundant species. The objectives of the current study were to develop an effective methodology for capturing juvenile lake sturgeon in a large riverine environment; to describe the physical habitat characteristics (depth, water velocity and substrate) associated with the areas where juvenile lake sturgeon were captured; and to determine basic population parameters (length, body mass and condition factor) for juvenile lake sturgeon captured in those areas. Gillnets (mesh sizes 25–108 mm) were used to sample the Winnipeg River, a large river in the northern extent of the species range, from 12 June to 6 November 2006. A total of 2154 juvenile (<530 mm FL) lake sturgeon were captured, which represented over 74% of the total fish catch. Moderate (51–108 mm) and small (25 mm) mesh gill nets were found to be efficient for sampling juvenile lake sturgeon, with the former capturing a wider range of sizes and the latter capturing fewer fish but resulting in decreased mortality. Juvenile lake sturgeon were captured at high densities in discrete areas characterized by water depths >13.7 m, detectable water velocities >0.20 m s⁻¹, and various substrate types.     

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.     

Short‐term freshwater exposure benefits sea lice‐infected Atlantic salmon

Atlantic salmon Salmo salar were infected with sea lice Lepeophtheirus salmonis (0·08 ± 0·007 sea lice g⁻¹) over a period of 4 h. Both infected and non‐infected fish were swim tested in sea water (SW) and fresh water (FW). The ventral aorta of each fish was fitted with a Doppler cuff in order to measure cardiac output, stroke volume and heart rate during swim testing. Blood samples were taken at rest and after exercise. Critical swimming speed of infected fish in SW (2·14 ± 0·08 body lengths, bl s⁻¹) was significantly lower ( P  < 0·05) than infected fish switched to FW (2·81 ± 0·08 bl s⁻¹) and non‐infected fish in SW (2·42 ± 0·04 bl s⁻¹) and FW (2·61 ± 0·08 bl s⁻¹). Cardiac and blood results indicated infected fish exposed to FW did experience stress, but relief from osmotic and ionic distress probably reduces energy expenditure, allowing the increase in performance. As the performance of sea lice‐infected fish improved upon transfer to FW, it is likely that heavily infected salmonids do return to FW to restore compromised osmotic and ionic balance, and remove sea lice in the process.     

Effect of increased flow on the behaviour of Atlantic salmon parr in winter

The effect of increased flow on movement and microhabitat use of Atlantic salmon Salmo salar parr in winter was investigated using radiotelemetry. To simulate hydropeaking operations, flow was increased four‐fold from 1·3 m³ s⁻¹ to 5·2 m³ s⁻¹ for 24 h periods. Flow did not affect fish habitat use or displacement and had little effect on fish activity within diel periods. During high flow periods in late winter, fish reduced night‐time activity. Stranding rates during flow reduction were also very low (only one fish).     

Anion exchange in the giant erythrocytes of African lungfish

Carbon dioxide transport in African lungfish Protopterus aethiopicus blood conformed to the typical vertebrate scheme, implying a crucial and rate-limiting role of erythrocyte Cl^–/HCO₃^– exchange. The rate coefficient for unidirectional Cl^– efflux via the anion exchanger ( k , s⁻¹) increased with temperature in African lungfish, but values were well below those reported in other species. The erythrocytes of African lungfish were, however, very large (mean cellular volume = 6940 µm³), and the ratio of cell water volume to membrane surface area was high ( V _w A _m⁻¹ = 1·89). Hence, the apparent Cl^– permeability ( P _Cl =  kV _w A _m⁻¹, µm s⁻¹) was close to that in other vertebrates. The plot of ln P _Cl against the inverse absolute temperature was left-shifted in the tropical African lungfish compared to the temperate rainbow trout Oncorhynchus mykiss , which supports the idea that P _Cl is similar among animals when compared at their preferred temperatures. Also, Q ₁₀ for anion exchange calculated from P _Cl values in African lungfish was 2·0, supporting the idea that the temperature sensitivity of erythrocyte anion exchange matches the temperature sensitivity of CO₂ production and transport in ectothermic vertebrates.     

Effects of regulated discharge on burbot migration

Burbot Lota lota movement and river discharge were studied in the Kootenai River, Idaho, U.S.A. and British Columbia, Canada, downstream of Libby Dam, Montana, U.S.A. A total of 24 adult burbot with transmitters were tracked from 1994 to 2000, for analysis of a travel distance of ≥5 km in ≤10 days termed 'stepwise movement'. Of 44 'stepwise movements', significantly greater movements during pre‐spawning and spawning were observed when average daily discharges from Libby Dam were <300 m³ s⁻¹, with a mean of 176 m³ s⁻¹, similar to pre‐dam conditions. Burbot travelled at a greater rate during all seasons (3·36 km day⁻¹) at discharges >300 m³ s⁻¹(mean = 1·84 km day⁻¹) than at discharges >300 m³ s⁻¹ but no difference was found for the pre‐spawning and spawning period. Burbot that started 'stepwise movements' in low discharge conditions frequently stopped during low discharges.     

Physiological impact of sea lice on swimming performance of Atlantic salmon

Atlantic salmon Salmo salar were infected with two levels of sea lice Lepeophtheirus salmonis (0·13 ± 0·02 and 0·02 ± 0·00 sea lice g⁻¹). Once sea lice became adults, the ventral aorta of each fish was fitted with a Doppler cuff to measure cardiac output ( ̇ ), heart rate ( f _H) and stroke volume ( V _S) during swimming. Critical swimming speeds ( U _crit) of fish with higher sea lice numbers [2·1 ± 0·1 BL (body lengths) s⁻¹] were significantly lower ( P  < 0·05) than fish with lower numbers (2·4 ± 0·1 BL s⁻¹) and controls (sham infected, 2·6 ± 0·1 BL s⁻¹). After swimming, chloride levels in fish with higher sea lice numbers (184·4 ± 11·3 mmol l⁻¹) increased significantly (54%) from levels at rest and were significantly higher than fish with fewer lice (142·0 ± 3·7 mmol l⁻¹) or control fish (159·5 ± 3·5 mmol l⁻¹). The f _H of fish with more lice was 9% slower than the other two groups at U _crit. This decrease resulted in ̇ not increasing from resting levels. Sublethal infection by sea lice compromised the overall fitness of Atlantic salmon. The level of sea lice infection used in the present study was lower than has previously been reported to be detrimental to wild Atlantic salmon.     

Migration of hatchery‐reared Atlantic salmon and wild anadromous brown trout post‐smolts in a Norwegian fjord system

Hatchery‐reared Atlantic salmon Salmo salar ( n  = 25) and wild anadromous brown trout (sea trout) Salmo trutta ( n  = 15) smolts were tagged with coded acoustic transmitters and released at the mouth of the River Eira on the west coast of Norway. Data logging receivers recorded the fish during their outward migration at 9, 32, 48 and 77 km from the release site. Seventeen Atlantic salmon (68%) and eight sea trout (53%) were recorded after release. Mean migratory speeds between different receiver sites ranged from 0·49 to 1·82 body lengths (total length) per second (bl s⁻¹) for Atlantic salmon and 0·11–2·60 bl s⁻¹ for sea trout. Atlantic salmon were recorded 9, 48 and 77 km from the river mouth on average 28, 65 and 83 h after release, respectively. Sea trout were recorded 9 km from the release site 438 h after release. Only four (23%) sea trout were detected in the outer part of the fjord system, while the rest of the fish seemed to stay in the inner fjord system. The Atlantic salmon stayed for a longer time in the inner part than in the outer parts of the fjord system, but distinct from sea trout, migrated through the whole fjord system into the ocean.     

Tracking Atlantic salmon smolts, Salmo salar L., through Loch Voil, Scotland

Twenty-two salmon smolts, Salmo salar L., carrying miniature sonic tags were tracked individually for periods of up to 175 h in Loch Voil, Scotland, during May 1979 and 1980. Activity was predominantly nocturnal, 80% occurring between 21.00 and 06.00 hours, and was apparently undirected. Average velocities during this active interval were 0.6 body lengths per second (bl s⁻¹), with 98 and 93% of the time spent moving at less than 2 and less than 1 bl s⁻¹, respectively. The rates of downstream displacement were 0.04 bl s⁻¹ in 1979 and 0.01 bl s⁻¹ in 1980. The direction of displacement of smolts and of movement of water at a depth of 1 m was positively correlated ( P <0.001) and smolt displacement was biassed slightly ahead of water movement. Mean step lengths were 141 and 200 m in 1979 and 1980, respectively. Rates of downstream passage of 327 ICES plate-tagged smolts released 16.8 km upstream of the fish trap at Clunie dam, Loch Tummel, during the spring migrations of 1975 and 1976 averaged 0.13 bl s⁻¹ in each year: net surface water movement was about 3.7 times this rate during the same intervals. These data are consistent with the model of passive smolt migration postulated by Tytler et al. (1978) and suggest that the active component required to ensure passage through a loch (Thorpe & Morgan, 1978) is very small.     

Electrical signalling and cytokinins mediate effects of light and root cutting on ion uptake in intact plants

Nutrient acquisition in the mature root zone is under systemic control by the shoot and the root tip. In maize, exposure of the shoot to light induces short-term (within 1–2 min) effects on net K⁺ and H⁺ transport at the root surface. H⁺ efflux decreased (from −18 to −12 nmol m⁻² s⁻¹) and K⁺ uptake (∼2 nmol m⁻² s⁻¹) reverted to efflux (∼−3 nmol m⁻² s⁻¹). Xylem probing revealed that the trans-root (electrical) potential drop between xylem vessels and an external electrode responded within seconds to a stepwise increase in light intensity; xylem pressure started to decrease after a ∼3 min delay, favouring electrical as opposed to hydraulic signalling. Cutting of maize and barley roots at the base reduced H⁺ efflux and stopped K⁺ influx in low-salt medium; xylem pressure rapidly increased to atmospheric levels. With 100 m m NaCl added to the bath, the pressure jump upon cutting was more dramatic, but fluxes remained unaffected, providing further evidence against hydraulic regulation of ion uptake. Following excision of the apical part of barley roots, influx changed to large efflux (−50 nmol m⁻² s⁻¹). Kinetin (2–4  µ m ), a synthetic cytokinin, reversed this effect. Regulation of ion transport by root-tip-synthesized cytokinins is discussed.     

Problems with the use of terracotta clay saucers as phosphorus-diffusing substrata to assess nutrient limitation of epilithic algae

1. We examined the diffusion properties of terracotta clay saucers, of types often used as components in phosphorus-diffusing substrata for investigating nutrient limitation of epilithic algae.
2. Laboratory experiments showed that phosphorus diffusion was low and inconsistent (0.06–2.6 mg P day⁻¹) through clay saucers filled with agar containing orthophosphate. Similarly, in situ release of phosphorus from two types of terracotta clay saucers (Australian and Italian) was variable (2–8 mg P day⁻¹; 5–25%) under three flow regimes (0, 0.1 and 0.3 m s⁻¹) over 30 days, with most phosphorus being released during the first day. Clogging of pores by agar appears to prevent the diffusion of phosphorus through the terracotta clay saucers. However, the two types of terracotta clay saucer also irreversibly sorbed large quantities of phosphorus (40–140 mg P).
3. Individual saucers can have markedly different physical and chemical properties both within and among terracotta types. Terracotta saucers also contain large quantities of iron, calcium and aluminium that are known binding agents for phosphorus. Variability in saucer composition and diffusion properties makes treatments difficult to replicate and weakens comparisons between studies that have used terracotta with different clay composition and manufacture.
4. We recommend that phosphorus-diffusing substrata should not be constructed from terracotta clay components.     

Swimming behavior in relation to buoyancy in an open swimbladder fish, the Chinese sturgeon

The swimbladder of fishes is readily compressed by hydrostatic pressure with depth, causing changes in buoyancy. While modern fishes can regulate buoyancy by secreting gases from the blood into the swimbladder, primitive fishes, such as sturgeons, lack this secretion mechanism and rely entirely on air gulped at the surface to inflate the swimbladder. Therefore, sturgeons may experience changes in buoyancy that will affect their behavior at different depths. To test this prediction, we attached data loggers to seven free-ranging Chinese sturgeons Acipenser sinensis in the Yangtze River, China, to monitor their depth utilization, tail-beating activity, swim speed and body inclination. Two distinct, individual-specific, behavioral patterns were observed. Four fish swam at shallow depths (7–31 m), at speeds of 0.5–0.6 m s⁻¹, with ascending and descending movements of 1.0–2.4 m in amplitude. They beat their tails continuously, indicating that their buoyancy was close to neutral with their inflated swimbladders. In addition, their occasional visits to the surface suggest that they gulped air to inflate their swimbladders. The other three fish spent most of their time (88–94%) on the river bottom at a depth of 106–122 m with minimum activity. They occasionally swam upwards at speeds of 0.6–0.8 m s⁻¹ with intense tailbeats before gliding back passively to the bottom, in a manner similar to fishes that lack a swimbladder. Their bladders were probably collapsed by hydrostatic pressure, resulting in negative buoyancy. We conclude that Chinese sturgeons behave according to their buoyancy, which varies with depth due to hydrostatic compression of the swimbladder.     

Endurance swimming of European eel

A long‐term swim trial was performed with five female silver eels Anguilla anguilla of 0·8–1·0 kg ( c . 80 cm total length, L _T) swimming at 0·5 body lengths (BL) s⁻¹, corresponding to the mean swimming speed during spawning migration. The design of the Blazka‐type swim tunnel was significantly improved, and for the first time the flow pattern of a swim tunnel for fish was evaluated with the Laser‐Doppler method. The velocity profile over three different cross‐sections was determined. It was observed that 80% of the water velocity drop‐off occurred over a boundary layer of 20 mm. Therefore, swim velocity errors were negligible as the eels always swam outside this layer. The fish were able to swim continuously day and night during a period of 3 months in the swim tunnel through which fresh water at 19° C was passed. The oxygen consumption rates remained stable at 36·9 ± 2·9 mg O₂ kg⁻¹ h⁻¹ over the 3 months swimming period for all tested eels. The mean cost of transportation was 28·2 mg O₂ kg⁻¹ km⁻¹. From the total energy consumption the calculated decline in fat content was 30%. When extrapolating to 6000 km this would have been 60%, leaving only 40% of the total energy reserves for reproduction after arriving at the spawning site. Therefore low cost of transport combined with high fat content are crucial for the capacity of the eel to cross the Atlantic Ocean and reproduce.     

Swimming performance, oxygen consumption and excess post-exercise oxygen consumption in adult transgenic and ocean-ranched coho salmon

Routine oxygen consumption ( M o ₂) was 35% higher in 1 day starved and 21% higher in 4 day starved adult transgenic coho salmon Oncorhynchus kisutch relative to end of migration ocean-ranched coho salmon. Critical swimming speed ( U _crit) and M o ₂ at U _crit ( M o _2max) were significantly lower in 4 day starved transgenic coho salmon (1·25 BL s⁻¹; 8·79 mg O₂ kg⁻¹ min⁻¹) compared to ocean-ranched coho salmon (1·60 BL s⁻¹; 9·87 mg O₂ kg⁻¹ min⁻¹). Transgenic fish swam energetically less efficiently than ocean-ranched fish, as indicated by a poorer swimming economy at U _crit ( M o _2max     ). Although M o _2max was lower in transgenic coho salmon, the excess post-exercise oxygen consumption (EPOC) measured during the first 20 min of recovery was significantly larger in transgenic coho salmon (44·1 mg O₂ kg⁻¹) compared with ocean-ranched coho salmon (34·2 mg O₂ kg⁻¹), which had a faster rate of recovery.