Calcium‐dependent behavioural responses to acute copper exposure in Oncorhynchus mykiss

Using rainbow trout Oncorhynchus mykiss, the present study demonstrated that: (1) calcium (Ca) increased the range of copper (Cu) concentrations that O. mykiss avoided; (2) Ca conserved the maintenance of pre‐exposure swimming activity during inescapable acute (10 min) Cu exposure. Data showed that when presented with a choice of Cu‐contaminated water (ranging from 0 to 454 µg Cu l^?1) and uncontaminated water in a choice tank, O. mykiss acclimated and tested at low Ca concentration (3 mg Ca l^?1) avoided the 10 µg Cu l^?1 only. By contrast, O. mykiss acclimated and tested at high Ca concentration (158 mg Ca l^?1) avoided all the Cu concentrations ≥37 µg l^?1. The Cu avoidance was connected with increased spontaneous swimming speed in the Cu‐contaminated water. When subjected to inescapable Cu exposure (35 µg Cu l^?1), O. mykiss acclimated and tested at low Ca concentration reduced their spontaneous swimming speed, whereas no response was observed in O. mykiss acclimated and tested at high Ca concentration. Collectively, the data support the conclusion that in O. mykiss the behavioural responses to acute Cu exposure are Ca‐dependent.     

Group swimming behaviour and energetics in bluegill Lepomis macrochirus and rainbow trout Oncorhynchus mykiss

Group swimming size influences metabolic energy consumption and swimming behaviour in fishes. Hydrodynamic flows and vortices of other fish are thought to be beneficial in terms of the energetic costs of swimming. Similarly, abiotic obstructions have been shown to have similar benefits with respect to metabolic consumption in swimming fish such as rainbow trout Oncorhynchus mykiss. The current study works to examine metabolic rates and swimming behaviours as a function of group swimming with bluegill sunfish Lepomis macrochirus and O. mykiss. Fishes were subjected to individual and group swimming in a respiratory swim tunnel to determine oxygen consumption as a proxy for the metabolic rate of swimming fish. In addition, fish movements within the swim tunnel test chamber were tracked to examine group swimming behaviour. We hypothesized that fish would benefit metabolically from group swimming. In the case of O. mykiss, we also hypothesized that groups would benefit from the presence of an abiotic structure, as has been previously observed in fish swimming individually. Our results suggest that the influence of group size on swimming metabolism is species specific. While L. macrochirus show decreased metabolic rate when swimming in a group compared to individually, O. mykiss did not show such a metabolic benefit from group swimming.     

Migration depths of adult steelhead Oncorhynchus mykiss in relation to dissolved gas supersaturation in a regulated river system

Adult steelhead Oncorhynchus mykiss tagged with archival transmitters primarily migrated through a large river corridor at depths >2 m interspersed with frequent but short (<5 min) periods closer to the surface. The recorded swimming depths and behaviours probably provided adequate hydrostatic compensation for the supersaturated dissolved gas conditions encountered and probably limited development of gas bubble disease (GBD). Results parallel those from a concurrent adult Chinook salmon Oncorhynchus tshawytscha study, except O. mykiss experienced greater seasonal variability and were more likely to have depth uncompensated supersaturation exposure in some dam tailraces, perhaps explaining the higher incidence of GBD in this species.     

Altered burst swimming in rainbow trout Oncorhynchus mykiss exposed to natural and synthetic oestrogens

Juvenile rainbow trout Oncorhynchus mykiss were exposed to two concentrations each of 17β‐oestradiol (E2; natural oestrogen hormone) or 17α‐ethinyl oestradiol (EE2; a potent synthetic oestrogen hormone) to evaluate their potential effects on burst‐swimming performance. In each of six successive burst‐swimming assays, burst‐swimming speed (U_burst) was lower in fish exposed to 0·5 and 1 µg l^?1 E2 and EE2 for four days compared with control fish. A practice swim (2 days prior to exposure initiation) in control fish elevated initial U_burst values, but this training effect was not evident in the 1 µg l^?1 EE2‐exposed fish. Several potential oestrogen‐mediated mechanisms for U_burst reductions were investigated, including effects on metabolic products, osmoregulation and blood oxygen‐carrying capacity. Prior to burst‐swimming trials, fish exposed to E2 and EE2 for 4 days had significantly reduced erythrocyte numbers and lower plasma glucose concentrations. After six repeated burst‐swimming trials, plasma glucose, lactate and creatinine concentrations were not significantly different among treatment groups; however, plasma Cl^? concentrations were significantly reduced in E2‐ and EE2‐treated fish. In summary, E2 and EE2 exposure altered oxygen‐carrying capacity ([erythrocytes]) and an osmoregulatory‐related variable ([Cl^?]), effects that may underlie reductions in burst‐swimming speed, which will have implications for fish performance in the wild.     

Effects of intracoelomic transmitter implantation on metabolic rate,swimming performance,growth and survival in juveniles of two salmonids

In this study, we investigated the effects of acoustic tag implantation on standard and routine metabolic rate (SMR and RMR, estimated via oxygen consumption), critical swimming speed (U_crit), survival and growth in juveniles of rainbow trout Oncorhynchus mykiss and lake trout Salvelinus namaycush. Tag burdens ranged from 1.8% to 7.5% across the two species. Growth rates in acoustic-tagged fish were equal to or higher than those in other treatments. Acoustic-tagged S. namaycush had a marginally lower U_crit than controls but that effect was not replicated in the O. mykiss experiment. Tagging did not have clear effects on metabolic rate but there was an interaction whereby SMR and RMR tended to increase with time since surgery in tagged O. mykiss but not in other treatments (the same trend did not occur in S. namaycush). Survival was high across treatments (mean 98% survival among O. mykiss, 97.5% among S. namaycush). There were no statistically significant effects of tag burden (percentage of body mass) except for a weak negative relationship with growth rate (across species) and a weak positive relationship with U_crit but only in the O. mykiss. Collectively, our findings suggest there were minor, context-dependent effects of acoustic tagging in juvenile S. namaycush and O. mykiss during an eight-week laboratory experiment. Further research will be required to assess whether tagging can cause meaningful behavioural effects in these species in captivity or in the wild and whether there is a tag burden threshold above which deleterious effects consistently occur.     

Hardness does not affect the physiological responses of wild and domestic strains of diploid and triploid rainbow trout Oncorhynchus mykiss to short‐term exposure to pH 9.5

This study examined the effects of water hardness on the physiological responses associated with high pH exposure in multiple strains of diploid and triploid rainbow trout Oncorhynchus mykiss. To accomplish this, three wild strains and one domesticated strain of diploid and triploid O. mykiss were abruptly transferred from control soft water (City of Vancouver dechlorinated tap water; pH 6·7; [CaCO₃] < 17·9 mg l^?1) to control soft water (handling control), high pH soft water (pH 9·5; [CaCO₃] < 17·9 mg l^?1), or high pH hard water (pH 9·5; [CaCO₃] = 320 mg l^?1) followed by sampling at 24 h for physiological measurements. There was a significant effect of ploidy on loss of equilibrium (LOE) over the 24 h exposure, with only triploid O. mykiss losing equilibrium at high pH in both soft and hard water. Furthermore, exposure to pH 9·5 resulted in significant decreases in plasma sodium and chloride, and increases in plasma and brain ammonia with no differences between soft and hard water. There was no significant effect of strain on LOE, but there were significant differences between strains in brain ammonia and plasma cortisol. Overall, there were no clear protective effects of hardness on high pH exposure in these strains of O. mykiss.     

Magnetic field perception in the Rainbow Trout, <Emphasis Type="Italic">Oncorhynchus</Emphasis> <Emphasis Type="Italic">mykiss</Emphasis>

In this study, we present evidence for the perception of different magnetic field parameters in a facultative anadromous fish species of the family Salmonidae. Magnetic field perception of the rainbow trout, Oncorhynchus mykiss, was demonstrated with a heartbeat conditioning test. The electrocardiogram was measured with subcutaneously inserted silver wire electrodes in freely swimming fish. We demonstrate a conditioned response (i.e. a significant longer interval between two heartbeats) to an intensity/inclination shift for three adult and two juvenile rainbow trouts. Moreover, a conditioned response to a 90° direction shift was demonstrated for three adult and two juvenile trouts. These findings support the hypothesis that the rainbow trout is able to perceive different magnetic field parameters. Furthermore, the study demonstrates magnetosensation in different developmental stages in the rainbow trout, i.e. juvenile and adult fish.     

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.     

Behavioral effects of environmental enrichment on harbor seals (Phoca vitulina concolor) and gray seals (Halichoerus grypus)

Zoos and aquariums have been incorporating environmental enrichment into their animal care programs for the past 30 years to increase mental stimulation and promote natural behaviors. However, most attempts to document the effects of enrichment on animal behavior have focused on terrestrial mammals. Staff at the National Aquarium in Baltimore conducted an investigation of the behavioral effects of enrichment on the seven harbor seals and two gray seals housed in the aquarium's outdoor seal exhibit. We expected that enrichment would change the amount of time the animals spent engaged in specific behaviors. The behaviors recorded were: resting in water, resting hauled out, maintenance, breeding display, breeding behavior, aggression, pattern swimming, random swimming, exploration, and out of sight. Activity levels (random swimming and exploration) were expected to increase, while stereotypic behaviors (pattern swimming) were expected to decrease. The frequency and duration of behaviors were documented for 90 hr in both the control phase (without enrichment) and the experimental phase (with enrichment). Statistically significant differences (P<0.05) in the time spent in pattern swimming, random swimming, exploration, and out of sight were observed between the two phases. With enrichment, pattern swimming and out of sight decreased, while random swimming and exploration behavior increased. These findings demonstrate that enrichment can promote behaviors (random swimming and exploration) that are likely to be normal for phocids in the wild, and that may contribute to the behavioral complexity of these seals in captivity. Zoo Biol 21:375–387, 2002. © 2002 Wiley‐Liss, Inc.     

Reduction in swimming performance in juvenile rainbow trout (Oncorhynchus mykiss) following sublethal exposure to pyrethroid insecticides

While the lethal toxicity of pyrethroid insecticides to fish is well documented, their sublethal physio-behavioral effects remain poorly characterized. Known pyrethroid-associated changes to insect neuromuscular function may translate into similar effects in fish, thereby altering swimming ability and affecting foraging, predator avoidance, and migration. Three experiments were conducted using critical (U_crit) and burst (U_max) swimming speeds to assess the sublethal effects of the pyrethroids permethrin and deltamethrin in juvenile rainbow trout (Oncorhynchus mykiss). Fish were exposed to deltamethrin (100, 200, or 300 ng/L) or permethrin (1, 2, or 3 μg/L) in water for 4 d, and assessed for swimming performance. Deltamethrin (200 and 300 ng/L) reduced U_crit, but not U_max, while both swim performance measurements were unaffected by permethrin. Subsequent experiments used only U_crit to assess deltamethrin exposure. In a time course experiment, deltamethrin (300 ng/L) reduced U_crit after 1 and 4 d of exposure, but after 7 d of exposure U_crit was fully recovered. Finally, deltamethrin (1, 2, or 3 μg/L) reduced U_crit after 1 h bath exposures similar to recommended protocols for deltamethrin based sea-lice treatment in aquaculture. The real-world implications of the revealed pyrethroid-associated swimming ability reductions in salmon may be important in areas close to aquaculture facilities.     

The skin of adult rainbow trout is not a significant site of ammonia clearance from the blood

We hypothesized that the skin acts as an extrabranchial route for ammonia excretion in adult rainbow trout (Oncorhynchus mykiss) following high environmental ammonia (HEA) exposure. Trunks of control or HEA-exposed trout were perfused with saline containing 0 or 1 mmol l⁻¹ NH₄⁺. Cutaneous ammonia excretion rates increased 2.5-fold following HEA exposure, however there was no difference in rates between trunks perfused with 0 or 1 mmol l⁻¹ NH₄⁺. The skin is therefore capable of excreting its own ammonia load, but it does not clear circulating ammonia from the plasma.     

Hypoxia tolerance variance between swimming and resting striped bass Morone saxatilis

Individual striped bass Morone saxatilis were each exposed in random order to aquatic hypoxia (10% air saturation) either while swimming at 50% of their estimated critical swimming speed (U_crit) or while at rest until they lost equilibrium. Individuals were always less tolerant of hypoxia when swimming (P < 0·01); the average fish was over five times more tolerant to the same hypoxia exposure when not swimming. There was no relationship between an individual's rank order of hypoxia tolerance (HT) under the two flow regimes, suggesting that different factors determine an individual's HT when at rest than when swimming.     

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.     

Cannibalism in non‐native brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss stream‐dwelling populations

Introduced and allopatric populations of brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss were sampled in Slovenia for stable isotope analysis to assess dietary niche shifts through ontogeny and estimate the propensity for cannibalism. Both S. trutta and O. mykiss are cannibals, with higher average relative contribution of conspecific assimilated energy for S. trutta (27·9%) compared with O. mykiss (7·7%). The smallest cannibal was 166 mm in the S. trutta population and 247 mm in the O. mykiss population.     

Chromosomal evolution in salmonids: a comparison of Atlantic salmon, brown trout, and rainbow trout R-band chromosomes

Replication banding technique was applied to the chromosomes of Salmo salar, Salmo trutta, and Oncorhynchus mykiss. The in vitro technique has proved more advantageous than the in vivo technique due to a higher number of bands obtained. The comparison of these replication banding patterns has revealed that some chromosomes of Salmo trutta karyotype appeared associated with Salmo salar and Oncorhynchus mykiss karyotypes by single chromosomal rearrangements.     

Differential effect of wave stress on the physiology and behaviour of native versus non-native benthic invertebrates

In fresh waters, non-native invertebrate species preferentially spread via navigation waterways, where they often dominate assemblages. Littoral habitats in navigation waterways are regularly exposed to ship-induced waves. We conducted experiments to test the effects of artificial wave exposure on the relative performance of wide-spread native and non-native species. We compared physiological and behavioural response variables (i.e. growth rate, glycogen content, feeding and swimming activity) of two amphipods (native Gammarus roeselii and non-native Dikerogammarus villosus) and two gastropods (native Bithynia tentaculata and non-native Physella acuta) subject to wave and control (i.e. no wave) treatment flumes across a 6-week period. Growth, and in part glycogen content (as a measure of energy storage), were significantly reduced after exposure to waves in native invertebrates, but not in non-native invertebrates. The reduction in growth may be associated with the disturbance effects of waves, such as the higher swimming activity of G. roeselii and lower food uptake of B. tentaculata. In comparison, the effective hiding behaviour observed for D. villosus and good swimming ability of P. acuta, were identified as important traits facilitating the successful colonisation of the harsh habitat conditions of littoral waterways. Our study demonstrates that artificial wave regimes may contribute significant selective pressure, thus explaining the observed dominance of non-native species in navigational waterways. The success of non-native species under the harsh hydraulic habitat conditions of these socio-economically driven ecosystems may consequently be traced directly to behavioural and/or physiological traits.     

Migration characteristics of hatchery and natural-origin <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> from the lower Mokelumne River,California

The lower Mokelumne River (LMR), located in the California Central Valley, supports a population of natural-origin Oncorhynchus mykiss. In addition, the Mokelumne River Fish Hatchery (Hatchery) contributes hatchery produced O. mykiss to the system annually. We conducted a 3 year acoustic tagging study to evaluate the migratory characteristics of LMR hatchery and natural-origin O. mykiss to the Pacific Ocean. Specifically, we analyzed downstream movement and migration rates, routes, and success of acoustically tagged O. mykiss of hatchery and natural origin under variable release locations in non-tidal and tidal habitats. Results from our study suggest there are significant differences in the proportion of hatchery and natural O. mykiss that demonstrate downstream movement. Fish origin, size, and release location all had a significant effect on whether an individual demonstrated downstream movement. Mokelumne origin O. mykiss that initiated downstream movement utilized numerous migration routes throughout the Delta during their migration towards the Pacific Ocean. We identified four primary migration pathways from the lower Mokelumne River through the Sacramento-San Joaquin Delta while the Delta Cross Channel was closed. However, several other pathways were utilized. Origin had a significant effect on O. mykiss success in reaching key points in the Delta and through the Estuary. Fish size had a significant effect on whether an individual reached the marine environment. Of the 467 O. mykiss tagged, 34 successfully reached the Pacific Ocean (Golden Gate Bridge), and of these, 33 were hatchery-origin and 1 was natural-origin. A higher proportion of hatchery-origin fish (10% of tagged) migrated to the ocean compared to natural-origin fish (<1%). Our study provides valuable information on the differences between hatchery and natural-origin O. mykiss migration characteristics as well as unique insight into the migratory behavior of little studied non-Sacramento River origin salmonids.     

Use of streambed substrate as refuge by steelhead or rainbow trout Oncorhynchus mykiss during simulated freshets

A flume was used to estimate the carrying capacity of streambed substrates for juvenile steelhead or rainbow trout Oncorhynchus mykiss seeking refuge from simulated freshets. The simulated freshets had mean water column velocities of c. 1·1 m s^?1. The number of O. mykiss finding cover within the interstices of the substrate was documented for different substrate sizes and levels of embeddedness. The availability of suitable refuges determined the carrying capacity of the substrate for O. mykiss. For the size of the O. mykiss tested [mean ± s.d. fork length (L_F) = 122 ± 12·6 mm], the number of interstices with depths ≥200 mm measured with a 14·0 mm diameter flexible plastic tube was the best predictor of the number of O. mykiss able to find cover (r² = 0·75). Oncorhynchus mykiss seeking refuge from freshets may need deeper interstices than those seeking concealment at autumn or winter base flows. The availability of interstices suitable as refuge from high flows may determine autumn and winter carrying capacity.     

Egg Cortisol Exposure Enhances Fearfulness in Larvae and Juvenile Rainbow Trout

We investigated the effects of an early boost of cortisol exposure in rainbow trout (Oncorhynchus mykiss) eggs during fertilisation on subsequent behavioural responses when exposed to a sudden stimulus in larvae and juveniles. At 55 d post‐fertilisation (dpf), treatment had no effect on high accelerations occurring after a sudden event. At 146 dpf, these high accelerations were more frequent in cortisol‐treated fish than in controls. At 146 dpf also, swimming activity was increased in cortisol‐treated fish both before and after the sudden stimulus. This study underlines the important behavioural modifications in both larvae and juveniles, linked to a change in the surrounding environment of the embryo. Indeed, fish exposed to cortisol as eggs showed a higher level of fearfulness later in life. Our findings are of major interest for stress management in an aquaculture context and also allow for a better understanding of the long‐lasting effects of a permanent and/or acute stress – mediated by cortisol – that could be encountered by females, affecting population's life history trajectory.     

Influence of Chlorella powder intake during swimming stress in mice

We used the forced swimming test to investigate the influence of Chlorella powder intake during muscle stress training in mice. After day 14, swimming time was about 2-fold longer for Chlorella intake mice than for control swimming mice. Microarray analysis revealed that the global gene expression profile of muscle from the Chlorella intake mice was similar to that of muscle from the intact (non-swimming) mice, and the profile of these two groups differed from that of the control (swimming) mice. Gene ontology and pathway analyses of gene expression data showed that oxidoreductase activity and the leukotriene synthesis pathway were repressed in the Chlorella intake mice following the swimming test. In addition, measurements of free fatty acids, glucose, triglycerides, and lactic acid in the blood of Chlorella intake mice were higher than that of control mice. These findings suggest that metabolism in tissues is altered by Chlorella intake.