Displacement,velocity preference,and substrate use of three native California stream fishes in simulated pulsed flows

We studied whether juvenile fishes were able to maintain swimming speed and position during simulated river pulsed flows in a laboratory flume. We used a glass flume (15.24 × 0.6 m) with river-rock substrate to determine the longitudinal displacement, movement distances and frequencies, velocity selection, and substrate use of juvenile (SL range: 6.1 ± 0.2 cm) hardhead Mylopharodon conocephalus (n = 13), rainbow trout Oncorhynchus mykiss (n = 11), and Sacramento sucker Catostomus occidentalis (n = 12) during a 100-min flow pulse, as velocity changed from slow to medium, fast, medium, and slow. Fish were capable of maintaining swimming speed and position up to the maximum flume velocity of 0.46 m·s⁻¹, except for one hardhead that impinged on the rear fish screen. Fish swam faster in the flume during the medium and fast intervals than the slow intervals, but fish speeds were similar among the medium and faster intervals, when some fish took cover behind the rock substrate. In comparison with a Brett-type swim-tunnel, fish showed less increase in mean swimming speed as the flume velocity increased. Fish in the flume were able to use the rock substrate as hydraulic cover, decreasing the encountered water velocity, and, presumably, conserving energy.     

Nested species subsets, gaps, and discrepancy

Chemical cues from fish can alter the behaviour of stream invertebrates in experimental tanks but their effect in natural streams has received little attention. By adding brook trout (Salvelinus fontinalis) odour to a trout stream in the Rocky Mountains of Colorado, USA, we tested whether changes in the concentration of chemical cues from visually feeding predatory fish would alter the drift of mayfly nymphs (Ephemeroptera). Stream water was piped from stream-side tanks with (odour) and without (control) three brook trout to two locations in the stream 3.5 m upstream of drift nets at six replicate sites. Five-minute drift samples were collected downstream from odour and control pipes before, during and after the release of water from the tanks into the stream during both the day and night. Almost all drift occurred at night and consisted predominantly of Baetis bicaudatus nymphs. The odour manipulation had no measurable effect on Baetis drift during the day but statistical power was low. During the night, however, the drift of large (>0.65 mm head capsule width, HCW) Baetis nymphs decreased significantly during the odour addition compared to control drift. In contrast, the drift of small nymphs (≤0.65 mm HCW) increased both during and after the odour addition in comparison to control drift. Since the stream contains brook trout (0.04–0.18 m⁻²), and water from the stream (presumably containing fish odour) altered the behaviour of fishless-stream Baetis nymphs in another experiment, we conclude that the changes in Baetis drift density were a response to an increase in the concentration of fish odour in the stream. Furthermore, we were able to detect the effect within 5 min. of odour addition, indicating that mayfly behavioural response to trout odour was rapid. These results suggest that mayflies can distinguish different concentrations of trout odour in natural streams and that the response is size-specific, according to the relative risk of predation of large and small Baetis. Received: 12 May 1998 / Accepted: 23 October 1998     

Fishing spiders, green sunfish, and a stream-dwelling water strider: male-female conflict and prey responses to single versus multiple predator environments

Many studies have experimentally addressed the effects of a particular predator species on prey behavior. In nature, however, prey frequently face multiple species of predators that often vary in their predatory mode and in their level of predation risk. Relatively few studies have considered prey responses under these complex conditions. In Kentucky, the stream-dwelling water strider (Aquariusremigis) coexists with many potentially dangerous predators, two of which are the green sunfish (Lepomiscyanellus) and the fishing spider (Dolomedesvittatus). Green sunfish occupy stream pools and attack water striders from below. In contrast, fishing spiders hunt along stream shorelines where they perch on overhanging vegetation or rocks and attack water striders near shore. We compared how A. remigis individuals respond to these two very different predators in pools with one or both predators. The presence of sunfish in pools had strong effects on male water strider behavior, including increased use of three types of refuge from sunfish (riffles, climbing out of the water, sitting on the water but at the edges of pools), decreased activity and a decreased number of aggressive males on the water. Spiders also influenced water strider behavior; male water striders avoided spiders by shifting away from the edges of pools. Comparisons of the effects of the two predator species showed that in general, antipredator responses by male water striders were stronger in pools with fish alone than in those with spiders alone. In the presence of both predators, male water strider behavior (microhabitat use and activity) was generally similar to behavior in the presence of fish alone. In contrast, female water striders showed no significant response to the presence of sunfish, and little response to the presence of spiders. This lack of response could be because females spent much of their time in refuges even in the absence of predators (apparently hiding from harassment by males). Both spiders and fish caused decreases in water strider mating activity. The presence of fish reduced both the number of matings per pool (mating frequency), and mean mating durations. Spiders induced a decrease in mean mating duration, but not in mating frequency. The largest reductions in mating activity occurred in pools with both predators present. Pools with either spiders or fish alone suffered 15–20% water strider mortality during our experiment (versus no mortality in predator-free pools). Extant theory suggests that when prey face conflicting microhabitat responses to two predators (as in this study), the predators should have facilitative effects on predation rates (i.e., prey that avoid one predator are often killed by the other and vice versa). Mortality rates in pools with both predators present, however, were not significantly different from that predicted by a null model of multiple predator effects. The lack of predator facilitation can be explained by the compensatory reductions in water strider activity and mating activity in the presence of both predators. Received: 26 August 1996 / Accepted: 12 June 1998     

Asymmetric competition between distant taxa: poecilid fishes and water striders

Summary Competition for water surface prey between fish (Priapichtus annectens: Poeciliidae) and water striders (Potamobates unidentatus: Gerridae) was studied in the laboratory and in pools in a small tropical stream. Laboratory experiments showed that fish depressed activity and foraging success of water striders. Large fish (4–5 cm) had a greater effect than small fish (2–3 cm). The field experiment showed that competition was highly asymmetric. Presence of fish decreased water strider foraging success while the reverse interaction was insignificant. It is suggested that the higher individual foraging success of the fish, harassment of water striders by fish and the use of an exclusive resource, benthic invertebrates, by the fish, contribute to this pattern. Habitat use differed between the two species. Fish used the deeper parts of stream pools and water striders used the shallower parts of the pools. Asymmetric interference and exploitation competition may force water striders to use shallow edge habitats.     

Pulses of soil phosphorus availability in a Mexican tropical dry forest: effects of seasonality and level of wetting

Intact cores from the upper soil profile and surface litter were collected at the peak of the dry season and during the rainy period in the tropical deciduous forest of the Chamela region, Jalisco, México, to (1) analyze upper soil phosphorus (P) movement and retention, (2) compare soil P dynamic pools (soluble, bicarbonate, and microbial) in dry and rainy seasons, and (3) determine the response of these P pools to wetting. Unperturbed litter-soil cores were treated in the laboratory with either 10 mm or 30 mm of simulated rain with carrier-free ³²P and compared to a control (no water addition) to determine the fate and retention of added P. ³¹P concentrations and pools in most litter and soil fractions were higher in the dry than in the rainy season. Soluble P was 0.306 g/m² and microbial P was 0.923 g/m² in the dry season (litter plus soil) versus 0.041 (soluble) and 0.526 (microbial) g P/m² in the rainy season. After water addition, rainy-season cores retained 99.9 and 94% of ³²P in the 10- and 30-mm treatments, respectively. Dry-season samples retained 98.9 and 80% of inputs in the same treatments. Retention after wetting occurred mostly in soil (bicarbonate and microbial fractions). Simulated rainfall on rainy-season soils increased P immobilization. On the other hand, simulated rainfall on dry-season soils released P through mineralization. The P release represents between 46 and 99% of the annual litterfall return. Our results suggest that both soluble and microbial P constitute important sources for initiation of plant growth at the onset of the rainy season in tropical dry forest. Received: 23 September 1997 / Accepted: 2 February 1998     

Effects of Predation Risk on Habitat Selection by Water Column Fish, Benthic Fish and Crayfish in Stream Pools

Predation risk can affect habitat selection by water column stream fish and crayfish, but little is known regarding effects of predation risk on habitat selection by benthic fish or assemblages of fish and crayfish. I used comparative studies and manipulative field experiments to determine whether, (1) habitat selection by stream fish and crayfish is affected by predation risk, and (2) benthic fish, water column fish, and crayfish differ in their habitat selection and response to predation risk. Snorkeling was used to observe fish and crayfish in, (1) unmanipulated stream pools with and without large smallmouth bass predators (Micropterus dolomieui >200 mm total length, TL) and (2) manipulated stream pools before and after addition of a single large smallmouth bass, to determine if prey size and presence of large fish predators affected habitat selection. Observations of microhabitat use were compared with microhabitat availability to determine microhabitat selection. Small fish (60–100 mm TL, except darters that were 30–100 mm TL) and crayfish (40–100 mm rostrum to telson length; TL) had significantly reduced densities in pools with large bass, whereas densities of large fish and crayfish (> 100 mm TL) did not differ significantly between pools with and without large bass. Small orangethroat darters (Etheostoma spectabile), northern crayfish (Orconectes virilis), and creek chubs (Semotilus atromaculatus) showed significantly greater densities in pools without large bass. The presence of large smallmouth bass did not significantly affect depths selected by fish and crayfish, except minnows, which were found significantly more often at medium depths when bass were present. Small minnows and large and small crayfish showed the greatest response to additions of bass to stream pools by moving away from bass locations and into shallow water. Small darters and sunfish showed an intermediate response, whereas large minnows showed no significant response to bass additions. Response to predation risk was dependent on prey size and species, with preferred prey, crayfish and small minnows, showing the greatest response. Small benthic fish, such as darters, are intermediate between small water column fish and crayfish and large water column fish in their risk of predation from large smallmouth bass.     

Spatial and vertical patterns in the tidepool fish assemblage on the island of O`ahu

The microtides, wave regimes, and relative isolation of the Hawaiian archipelago may provide unique environmental and biogeographic effects that shape the structure of tidepool fishes. We sampled fishes across a narrow gradient at low tide from 6 sites on the island of O`ahu. We tested predictions of the hypotheses that environmental conditions (pool depth, volume, macroalgal cover, temperature, and salinity) would result in a vertically structured tidepool fish assemblage unique to basalt or limestone rocky shores. 343 fish were recorded from 40 pools, and 19 species from 10 families were identified. Tidepool fish diversity (H’: O`ahu = 2.4; Sites Average = 0.0–0.9) was typical for tropical islands, with members from Gobiidae (5 species), Blenniidae (4 species), Pomacentridae (3 species), Acanthuridae (2 species) and Kuhliidae (2 species) among the most common. Endemism (32%) was higher than other well studied assemblages yet similar to Hawaiian reef fishes (25%). Assemblage abundance varied among shores with basalt or limestone substrate, among sites, and vertically among high, mid, and low pools. In general, blenniids occurred at higher proportions on limestone shores and gobiids were more common on basalt shores. High pools were characterized by an abundance of a small sized (29.0 mm median standard length) blenniid Istiblennius zebra, while the blenniid Entomacrodus marmoratus and wrasses Thalassoma spp. were more common in low pools. Temperature was the best environmental predictor of assemblages and this relationship warrants further investigation. Our findings indicate that assemblages can vary across a narrow geographical range and intertidal shore.     

Environmental Biology of an Endemic Cyprinid,Varicorhinus alticorpus,in a Subtropical Mountain Stream of Taiwan

An endemic freshwater fish, Varicorhinus alticorpus, was studied from 1990 to 1993 in a fast flowing mountain stream in southern Taiwan (22°30'N, 120°30'E). The analysis of environmental conditions suggested that the fish could tolerate water temperatures between 19–24°C, a pH of 8.0–8.8, and flow velocity from 20–100cmsec^–1. The fish occupied riffles and pools. They foraged and schooled during daytime and aggregated in crevices between rocks at night. Most juveniles stayed at the shallow sandy-pebble flat by the pool where flow was slow. The species feed primarily on the periphyton growing on the rocks, and leave unique scars after grazing. One peak of juvenile recruitment was observed right after the rainy season, suggesting that reproduction of the fish has adapted to the climate. The change of abundance of adults along the habitats (at 150 to 800 m altitude) also indicated that the fish might migrate to low altitudes for spawning and disperse back to higher altitudes for exploiting new resources. The environmental biology of this fish shows an example of a cyprinid adapted to habitats in a subtropical mountain stream.     

Involvement of Cd Bioaccumulation in Spinal Deformities Occurrence in Natural Populations of Mediterranean Killifish

The aim of this study was to investigate the possible influence of environmental exposure to cadmium (Cd) on the spinal deformities occurrence in the Mediterranean killifish, Aphanius fasciatus (Pisces: Cyprinodontidae). For this purpose, some indicators of skeletal bone mineralization, Cd, and calcium (Ca) concentrations in spinal column as well as bioaccumulation of Cd from the water and the sediment have been compared in normal and deformed fish collected from polluted (S1) and nonpolluted (S2) areas in the Gulf of Gabès in Tunisia. When compared to the normal fish, the deformed fish showed signs of spinal column demineralization such as significant decrease in the ash weight/dry weight ratio, percentage of nonorganic components content, and Ca concentration. Cd concentrations in spinal column and liver were significantly higher in deformed fish than in normal fish. A highly significant negative correlation (r = −0.915, p < 0.01) between Cd and Ca concentrations was noted in spinal column of deformed fish. Bioaccumulation factors of Cd in the liver from the water and the sediment in deformed fish were also significantly higher (p < 0.0001) than in normal fish from S1 and S2. These findings suggest that the ability to accumulate large amount of Cd may represent a potential risk to induce spinal deformities in natural populations of Mediterranean killifish.     

Short-term cues used by foraging trout in a California stream

Stream salmonids choose foraging locations to maximize the energy benefit of foraging within the constraints of size-mediated dominance hierarchies and predation risk. But, because stream habitats are temporally variable, fish must use a search process to monitor changing habitat conditions as a means of locating potentially-better foraging locations. I explored the cues used by the cutthroat trout, Oncorhynchus clarki clarki, when searching for food at the pool scale by artificially increasing prey availability at different locations by using special feeders and by manipulating pool velocities. Behavior of individually marked fish was monitored from stream bank platforms under unmanipulated control conditions and under seven experimental sets of conditions involving different combinations of feeder location and velocity manipulation. Under natural conditions fish elected to forage in the deepest (>50 cm), fastest (0.10–0.25 m s⁻¹) locations and within 1 m of structure cover, but would readily move to shallower (<30 cm) water away from cover if velocities were manipulated to be highest there. Although fish did not locate feeders unless they were placed in high-velocity areas, when high velocity was provided fish would move into very shallow water (<20 cm) if prey were delivered there. Responses of individual trout to manipulations indicated that water velocity was the main physical cue used by fish to decide where to forage, and that fish could also learn about new food sources by observing conspecifics. Overall, results indicated fish were not “perfect searchers” that could quickly locate new food resources over short time scales, even when the new resources were within a few meters of the fish’s normal foraging location. When given the correct cues, however, fish could detect new food sources and defend them against subordinate fish. Movement of new fish into and out of the study pools during the ten-day observation period was common, consistent with the idea that trout used movement as a means of exploring and learning about habitat conditions at the reach scale.     

Variation in carbon isotope composition among years in the riparian tree Populus fremontii

Water availability is an important factor limiting the productivity of desert plants but little is known about the impact of water-limiting conditions on the physiology of plants in mesic environments. Riparian ecosystems of the western US receive significantly more water than the surrounding desert environments but experience dramatic interannual fluctuations in water availability because both stream flow and precipitation are highly variable over time. This variability results in different growing conditions each year which may influence the physiology of riparian species such as Fremont cottonwood (Populus fremontii), the dominant, native canopy tree species in lowland southwestern US river systems. We wished to determine if the physiology of this species varies among years, what climatic parameters are related to any observed physiological variation and if individuals within a P. fremontii population differ in their physiological response to variation through time. We collected tree ring cores from a central New Mexico cottonwood population and analyzed carbon isotope composition (δ¹³C) in each year from 1981 to 1995. We used δ¹³C analysis in this study because it allowed us to obtain multi-year estimates of physiological activity. During these years, mean stream flow at our study site ranged over two orders of magnitude from 0.82 to 80.94 m³ s⁻¹, precipitation ranged fourfold from 49 to 215 ccmm and mean temperature ranged from 20.5 to 22.6°C during the growing season. δ¹³C varied from a low of −26.7‰ in 1984 to a high of −24.7‰ in 1981. Low δ¹³C values were associated with years in which stream flow and/or precipitation were high and temperature was low. The opposite was true of years with high δ¹³C values. We observed a strong linear relationship between δ¹³C and stream flow during years when stream flow was <25 m³ s⁻¹ but no significant relationship between these variables when stream flow was >25 m³ s⁻¹. Additionally, there was a linear relationship between δ¹³C and precipitation during years when stream flow was <25 m³ s⁻¹ but not in years when stream flow was >25 m³ s⁻¹. These data suggest that above a threshold of total stream flow, increased flow does not influence physiology. Below this threshold, precipitation can be an important water source. The ten individuals within our study population varied significantly in mean δ¹³C values but responded to interannual variation in a similar manner (i.e., all individuals had low δ¹³C values when water was abundant). These results suggest that precipitation as well as stream flow are important factors influencing the physiology of this riparian tree. Received: 25 November 1998 / Accepted: 9 February 1999     

Fish species richness and incidence patterns in isolated and connected stream pools: effects of pool volume and spatial position

I tested the effects of pool size and spatial position (upstream or downstream) on fish assemblage attributes in isolated and connected pools in an upland Oklahoma stream, United States. I hypothesized that there would be fundamental differences between assemblages in these two pool types due to the presence or absence of colonization opportunities. Analyses were carried out at three ecological scales: (1) the species richness of pool assemblages, (2) the species composition of pool assemblages, and (3) the responses of individual species. There were significant species-volume relationships for isolated and connected pools. However, the relationship was weaker and there were fewer species, on average, in isolated pools. For both pool types, species incidences were significantly nested such that species-poor pools tended to be subsets of species-rich pools, a common pattern that ultimately results from species-specific differences in colonization ability and/or extinction susceptibility. To examine the potential importance of these two processes in nestedness patterns in both pool types, I made the following two assumptions: (1) probability of extinction should decline with increasing pool size, and (2) probability of immigration should decline in an upstream direction (increasing isolation). When ordered by pool volume, only isolated pools were significantly nested suggesting that these assemblages were extinction-driven. When ordered by spatial position, only connected pools were significantly nested (more species downstream) suggesting that differences in species-specific dispersal abilities were important in structuring these assemblages. At the individual-species level, volume was a significant predictor of occurrence for three species in isolated pools. In connected pools, two species showed significant position effects, one species showed a pool volume effect, and one species showed pool volume and position effects. These results demonstrate that pool size and position within a watershed are important determinants of fish species assemblage structure, but their importance varies with the colonization potential of the pools. Isolated pool assemblages are similar to the presumed relaxed faunas of montane forest fragments and land bridge islands, but at much smaller space and time scales. Received: 6 December 1996 / Accepted: 10 December 1996     

Patchiness in the abundance of metacercariae parasitizingPoecilia gillii (Poeciliidae) isolated in pools of an intermittent tropical stream

Synopsis Prevalence and intensity of a clinostomatid in the fishPoecilia gilliii were measured in six dry season pools of a small intermittent Costa Rican stream, and the prevalence of two diplostomulid parasites (‚diplostomulum’ and ‚neascus’) were monitored in 14 residual pools of a second intermittent stream of the same drainage. There were significant among-pool differences in the prevalence of the three parasites. There was no evidence to suggest that clinostomatid or ‚diplostomulum’ prevalence was influenced by the position of pools within the downstream gradient; however, ‚neascus’ prevalence tended to decrease with distance downstream. Host length accounted for some of the variation in parasite prevalence among pools for both diplostomulids. Prevalence and intensity of a clinostomid in the body cavity varied with host gender and body size. There was a positive relationship between body size and clinostomatid parasitization in female hosts. Most males examined were less than 50 mm (total length). For fish less than 50 mm, males were more parasitized than females. Prevalence of the two diplostomulids was not related to the relative net periphyton production or the dissolved oxygen concentration of the pools. However, a positive correlation between the density ofP. gillii and ‚diplostomulum’ prevalence was found across the fourteen pools, and ‘neascus’ prevalence was positively related to pool area.     

No quarter: Lack of refuge during flow intermittency results in catastrophic mortality of an imperiled minnow

1. Many once-perennial rivers have become intermittent. Channel drying can result in fish mortality if refuges are not available. Understanding where refuges occur and if fishes use these refuges can provide insight for species persistence and help stakeholders manage limited resources. Streamflow diversions in the Rio Grande of New Mexico can result in >60 km losses of aquatic habitat, affecting up to 30% of the range of imperiled Rio Grande silvery minnow (Hybognathus amarus). Potential refuges include areas with perennial flow below diversion dams, isolated pools, and irrigation return flows.
2. We examined spatial and temporal patterns of both adult and young-of-year Rio Grande silvery minnow collected in isolated pools that formed during streamflow intermittency from 2009 to 2019. We hypothesised that: (1) Rio Grande silvery minnow would be more numerous in pools that persisted longer; (2) they would be more numerous in isolated pools located closer to upstream areas of perennial flow, due to upstream movement to escape drying; and (3) increased rate of aquatic habitat loss each day would result in more Rio Grande silvery minnow in isolated pools.
3. During the 12 years of the study, we counted Rio Grande silvery minnow in 3,985 isolated pools that formed during streamflow intermittency. We related counts of Rio Grande silvery minnow in each pool to the maximum pool depth, rate of loss of aquatic habitat that occurred that day, and distance each pool was to an upstream barrier. In 2016, we examined persistence of 290 isolated pools until complete desiccation or reconnection with continuous flows occurred, and the factors that influenced pool persistence.
4. Deeper pools persisted for longer, but depth had a small positive effect on counts of adult Rio Grande silvery minnow and no effect on counts of young-of-year in isolated pools. Adults were more numerous in upstream isolated pools, whereas young-of-year were more numerous in downstream isolated pools. Rate of channel drying had little effect on the numbers of adult Rio Grande silvery minnow in isolated pools, but more young-of-year were stranded when the rate of drying was faster. On average, pools persisted <4 days and 263 of 290 dried completely before continuous flows returned. Only 66 of 4,749 Rio Grande silvery minnow occurred in pools that did not dry completely.
5. Rio Grande silvery minnow did not appear to escape channel intermittency; instead, they became stranded in shrinking isolated pools that did not persist long enough to act as refuges for fishes. Lack of refuge during channel intermittency would result in catastrophic mortality of fishes through complete desiccation of pools if there were no management actions, such as translocating fish. To increase persistence through streamflow intermittency, conservation actions should match the species response to intermittency by ensuring the availability of perennial-water refuges at the appropriate spatial and temporal scale.

     

Immature Pacific bluefin tuna, <Emphasis Type="Italic">Thunnus orientalis</Emphasis>, utilizes cold waters in the Subarctic Frontal Zone for trans-Pacific migration

The habitat and movements of a Pacific bluefin tuna were investigated by reanalyzing archival tag data with sea surface temperature data. During its trans-Pacific migration to the eastern Pacific, the fish took a direct path and primarily utilized waters, in the Subarctic Frontal Zone (SFZ). Mean ambient temperature during the trans-Pacific migration was 14.5 ± 2.9 (°C ± SD), which is significantly colder than the waters typically inhabited by bluefin tuna in their primary feeding grounds in the western and eastern Pacific (17.6 ± 2.1). The fish moved rapidly through the colder water, and the heat produced during swimming and the thermoconservation ability of bluefin tuna likely enabled it to migrate through the cold waters of the SFZ.     

Body size, sex ratio and diet composition of Arctogadus glacialis (Peters, 1874) (Pisces: Gadidae) in the Northeast Water Polynya (Greenland)

Little is known about the biology and feeding ecology of Arctogadus glacialis (Peters, 1874), an endemic gadid fish species occurring circumpolarly in both ice-free and ice-covered Arctic seas. In this study we analysed specimens sampled from bottom trawl and Agassiz trawl catches conducted at eight stations in water depths from 115 to 490 m in the Northeast Water Polynya off Greenland in August 1990. Size composition and sex ratios were assessed for 585 fish with standard lengths ranging from 7.8 to 34.5 cm. Median fish sizes at the stations ranged between 8.6 and 18.8 cm. Quantitative stomach content analyses of a subsample of 175 specimens revealed that in the Northeast Water A. glacialis fed almost exclusively on pelagic prey. Truly benthic organisms were not found in the stomachs, and sympagic species were rarely recorded. Overall, calanoid copepods were the major prey in terms of numbers. However, stomach contents varied considerably between fish size groups. In terms of prey biomass, copepods dominated the diet of small fish (<12 cm), primarily occurring at shallow stations (115–250 m), whereas amphipods and mysids were relatively more important for larger fish (>16 cm), which dominated the catches at deep stations (360–480 m). The broad variety of diet composition indicated an opportunistic pelagic feeding pattern. Received: 6 November 1997 / Accepted: 11 May 1998     

Copper exposure impairs intra- and extracellular acid-base regulation during hypercapnia in the fresh water rainbow trout (Oncorhynchus mykiss)

In order to evaluate the impact of water-borne copper on acid-base regulation in fresh water rainbow trout, chronically cannulated fish were exposed to copper (0.6 mg 1⁻¹), hypercapnia (water PCO₂ of 6 mmHg) or a combination of copper and hypercapnia, while a fourth untreated group served as the control. Blood samples obtained at 0 h, 4 h and 24 h were analysed for acid-base status, ion concentrations and respiratory parameters. Tissue samples from caudal skeletal muscle, liver and gill filaments were examined for intracellular acid-base status, ion- and water contents, and copper concentration. Exposure to copper alone elicited a small extracellular metabolic alkalosis, no changes in arterial PO₂, and a minor decrease in plasma ion concentrations. Hypercapnia alone increased arterial PCO₂ from approximately 2 mmHg to 7.2 mmHg, but the extracellular respiratory acidosis present at 4 h was almost completely compensated at 24 h due to an increase in plasma bicarbonate concentration [HCO₃ ⁻] from 8.1 mM to 24.4 mM. Combined exposure to hypercapnia and copper resulted in a slightly larger acidosis at 4 h, and the fish failed to restore extracellular pH at 24 h, because plasma [HCO₃ ⁻] only increased to 16.3 mM. Fish exposed to hypercapnia and copper also showed a delayed recovery of intracellular pH in skeletal muscle, compared to fish exposure to hypercapnia only. Thus, copper exposure impaired both extracellular and intracellular acid-base regulation during hypercapnia. When seen in connection with only minor effects of copper on osmoregulatory and respiratory parameters, the reduced ability to regulate acid-base suggests that acid-base regulation may be one of the most copper-sensitive branchial functions. Accepted: 18 August 1998     

Distribution and movement of domestic rainbow trout, <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>, during pulsed flows in the South Fork American River,California

We tracked the movements of ten small (SL = 25.5–31.0 cm) and ten large (SL = 32.0–38.5 cm) radio-tagged domestic rainbow trout (Oncorhynchus mykiss) in response to frequent pulsed releases of water in the South Fork American River (California) from July to October 2005. In week one all the small trout moved less than 1 km upstream or downstream of their release sites. Four small trout moved 1–3 km upstream or downstream of their release sites in the following 8 weeks. Seven out of ten large trout moved downstream after their release. In subsequent weeks most large trout showed smaller upstream and downstream movements, and were observed between 1 km upstream and 8 km downstream of their release sites. Our results suggest that domestic rainbow trout with SL > 25 cm are not forced downstream by daily pulsed flow increases from 5 to over 40 m³s⁻¹.     

Rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> energetic responsesto pulsed flows in the American River,California, assessed by electromyogram telemetry

Although rainbow trout Oncorhynchus mykiss within the American River, California, apparently exhibit minimal upstream or downstream movements in response to hydroelectric-power-generation-related pulsed flows, the associated energetic costs are unknown. We implanted rainbow trout (n = 9, ≥30 cm SL) with electromyogram (EMG)-sensor-equipped radio transmitters to assess the swimming behavior and associated energetic costs associated with their responses to pulsed flows. Using laboratory calibrations in a Brett-type swimming respirometer, the trouts’ swimming speeds and oxygen consumption rates were estimated for their in-river EMG data, through a complete hydroelectric power-generation river pulsed-flow sequence (pre-pulse, increasing flow, peak, and decreasing flow stages), on several (mean: 3.2) sampling dates. Using a mixed-linear model, we found that fish swimming speed estimates increased during the increasing flow stage, while the associated mean oxygen consumption rates also increased at this stage. At river flows near the usual peak (>44 m³s⁻¹), swimming speeds and movement rates decreased, possibly due to the fish using the river’s habitat complexities as hydraulic cover. We conclude that rainbow trout incur increased swimming-related energetic costs during increasing flows and, potentially, decreased foraging opportunities at high flows.     

Molecular dynamics simulations of Nafion and sulfonated polyether sulfone membranes. I. Effect of hydration on aqueous phase structure

We measured the water uptakes and proton conductivities of a Nafion membrane and three sulfonated polyether sulfone membranes (SPESs) with different values of ion-exchange capacity (IEC = 0.75, 1.0 and 1.4 meq/g) in relation to relative humidity in order to apply the findings to polymer electrolyte membrane fuel cells. The number of water molecules per sulfonic acid group λ at each humidity level was independent of the relative humidity for all membranes, but the proton conductivities of the SPESs were inferior to that of Nafion for the same λ value. Classical molecular dynamics simulations for the same membranes were carried out using a consistent force field at λ = 3, 6, 9, 12 and 15. The structural properties of water molecules and hydronium ions at a molecular level were estimated from radial distribution functions and cluster size distributions of water. We found that the radial distribution function of S(sulfonic acid)–S(sulfonic acid) of Nafion at λ = 3 indicated a significant correlation between the S–S pair, due to water channels, while the S–S pair of the SPESs showed a poor correlation. The cluster size distribution of water was also calculated in order to estimate the connectivity of the water channel. It is clear that some water is present in the SPESs as small, isolated clusters, especially when the water content is low.