Natural soundscapes of lowland river habitats and the potential threat of urban noise pollution to migratory fish.

Migratory fish populations have experienced great declines, and considerable effort have been put into reducing stressors, such as chemical pollution and physical barriers. However, the importance of natural sounds as an information source and potential problems caused by noise pollution remain largely unexplored. The spatial distribution of sound sources and variation in propagation characteristics could provide migratory fish with acoustic cues about habitat suitability, predator presence, food availability and conspecific presence. We here investigated the relationship between natural soundscapes and local river conditions and we explored the presence of human-related sounds in these natural soundscapes. We found that 1a) natural river sound profiles vary with river scale and cross-sectional position, and that 1b) depth, width, water velocity, and distance from shore were all significant factors in explaining local soundscape variation. We also found 2a) audible human activities in almost all our underwater recordings and urban and suburban river parts had elevated sound levels relative to rural river parts. Furthermore, 2b) daytime levels were louder than night time sound levels, and bridges and nearby road traffic were much more prominent with diurnal and weekly patterns of anthropogenic noise in the river systems. We believe our data show high potential for natural soundscapes of low-land river habitat to serve as important environmental cues to migratory fish. However, anthropogenic noise may be particularly problematic due to the omnipresence, and relatively loud levels relative to the modest dynamic range of the natural sound sources, in these slow-flowing freshwater systems.

Tsc1 Haploinsufficiency Leads to Pax2 Dysregulation in the Developing Murine Cerebellum.

Tuberous sclerosis complex 1 (TSC1) is a tumor suppressor that promotes the inhibition of mechanistic target of rapamycin (mTOR) pathway, and mutations in TSC1 lead to a rare complex disorder of the same name. Despite phenotype heterogeneity, up to 50% of TSC patients present with autism spectrum disorder (ASD). Consequently, TSC models are often used to probe molecular and behavioral mechanisms of ASD development. Amongst the different brain areas proposed to play a role in the development of ASD, the cerebellum is commonly reported to be altered, and cerebellar-specific deletion of Tsc1 in mice is sufficient to induce ASD-like phenotypes. However, despite these functional changes, whether Tsc1 haploinsufficiency affects cerebellar development is still largely unknown. Given that the mTOR pathway is a master regulator of cell replication and migration, we hypothesized that dysregulation of this pathway would also disrupt the development of cell populations during critical periods of cerebellar development. Here, we used a mouse model of TSC to investigate gene and protein expression during embryonic and early postnatal periods of cerebellar development. We found that, at E18 and P7, mRNA levels of the cerebellar inhibitory interneuron marker paired box gene 2 (Pax2) were dysregulated. This dysregulation was accompanied by changes in the expression of mTOR pathway-related genes and downstream phosphorylation of S6. Differential gene correlation analysis revealed dynamic changes in correlated gene pairs across development, with an overall loss of correlation between mTOR- and cerebellar-related genes in Tsc1 mutants compared to controls. We corroborated the genetic findings by characterizing the mTOR pathway and cerebellar development on protein and cellular levels with Western blot and immunohistochemistry. We found that Pax2-expressing cells were largely unchanged at E18 and P1, while at P7, their number was increased and maturation into parvalbumin-expressing cells delayed. Our findings indicate that, in mice, Tsc1 haploinsufficiency leads to altered cerebellar development and that cerebellar interneuron precursors are particularly susceptible to mTOR pathway dysregulation.

Detailed Analysis of Zebrafish Larval Behaviour in the Light Dark Challenge Assay Shows That Diel Hatching Time Determines Individual Variation.

Research on stress coping style, i.e., the response of an organism to adverse conditions, which is constant over time and context, gained momentum in recent years, to better understand behavioural patterns in animal welfare. However, knowledge about the ontogeny of stress coping style is still limited. Here, we performed a detailed analysis of the light dark challenge behavioural assay in zebrafish larvae, where after acclimation in ambient light sudden alternating dark and light phases elicit an anxiety-like response. A principal component analysis on parameters related to locomotion (distance moved, swimming velocity, acceleration, mobility) and directionality (angular velocity, meandering of swimming path) revealed independence between the parameters determined in the light and the dark phases of the assay, indicating unrelated generalised behaviours per phase. However, high collinearity was observed between behavioural parameters within the same phase, indicating a robust response to the stimulus within behavioural phenotypes. Subsequently, this assay was used to determine the correlation between individual hatching time and the behavioural phenotype. The results show that fish that had hatched during daytime have a stronger behavioural response to the dark phase at 5 days post-fertilisation in locomotion related parameters and a weaker response in directionality related parameters, than fish that had hatched during nighttime. These results show that behavioural responses to the light dark challenge assay are robust and can be generalised for the light and the dark phase, and that diel hatching time may determine the behavioural phenotype of an individual.

Consequences of excessive glucosylsphingosine in glucocerebrosidase-deficient zebrafish.

In Gaucher disease (GD), the deficiency of glucocerebrosidase causes lysosomal accumulation of glucosylceramide (GlcCer), which is partly converted by acid ceramidase to glucosylsphingosine (GlcSph) in the lysosome. Chronically elevated blood and tissue GlcSph is thought to contribute to symptoms in GD patients as well as to increased risk for Parkinson's disease. On the other hand, formation of GlcSph may be beneficial since the water soluble sphingoid base is excreted via urine and bile. To study the role of excessive GlcSph formation during glucocerebrosidase deficiency, we studied zebrafish that have two orthologs of acid ceramidase, Asah1a and Asah1b. Only the latter is involved in the formation of GlcSph in glucocerebrosidase-deficient zebrafish as revealed by knockouts of Asah1a or Asah1b with glucocerebrosidase deficiency (either pharmacologically induced or genetic). Comparison of zebrafish with excessive GlcSph (gba1-/- fish) and without GlcSph (gba1-/-:asah1b-/- fish) allowed us to study the consequences of chronic high levels of GlcSph. Prevention of excessive GlcSph in gba1-/-:asah1b-/- fish did not restrict storage cells, GlcCer accumulation, or neuroinflammation. However, GD fish lacking excessive GlcSph show an ameliorated course of disease reflected by significantly increased lifespan, delayed locomotor abnormality, and delayed development of an abnormal curved back posture. The loss of tyrosine hydroxylase 1 (th1) mRNA, a marker of dopaminergic neurons, is slowed down in brain of GD fish lacking excessive GlcSph. In conclusion, in the zebrafish GD model, excess GlcSph has little impact on (neuro)inflammation or the presence of GlcCer-laden macrophages but rather seems harmful to th1-positive dopaminergic neurons.

The importance of individual variation for the interpretation of behavioural studies: ethanol effects vary with basal activity level in zebrafish larvae.

Standardization and reduction of variation is key to behavioural screening of animal models in toxicological and pharmacological studies. However, individual variation in behavioural and physiological phenotypes remains in each laboratory population and can undermine the understanding of toxicological and pharmaceutical effects and their underlying mechanisms. Here, we used zebrafish (ABTL-strain) larvae to explore individual consistency in activity level and emergence time, across subsequent days of early development (6-8 dpf). We also explored the correlation between these two behavioural parameters. We found inter-individual consistency over time in activity level and emergence time, but we did not find a consistent correlation between these parameters. Subsequently, we investigated the impact of variation in activity level on the effect of a 1% ethanol treatment, suitable for our proof-of-concept case study about whether impact from pharmacological treatments might be affected by inter-individual variation in basal locomotion. The inter-individual consistency over time in activity level did not persist in this test. This was due to the velocity change from before to after exposure, which turned out to be a dynamic individual trait related to basal activity level: low-activity individuals raised their swimming velocity, while high-activity individuals slowed down, yielding diametrically opposite response patterns to ethanol exposure. We therefore argue that inter-individual consistency in basal activity level, already from 6 dpf, is an important factor to take into account and provides a practical measure to improve the power of statistical analyses and the scope for data interpretation from behavioural screening studies.

The role of the Glucocorticoid Receptor in the Regulation of Diel Rhythmicity.

Virtually all organisms have adapted to the earth's day-night cycles by the evolution of endogenous rhythms that regulate most biological processes. Recent research has highlighted the role of glucocorticoids and the Glucocorticoid receptor (GR) in coordinating clock function across various levels of biological organisation. In the present study, we have explored the role of the GR in the rhythmicity of the biological clock, by comparing 5 day old wildtype zebrafish larvae (gr+) with mutant larvae with a non-functional GR (grs357). The mutants display a weaker rhythmicity in locomotor activity in wildtypes than in mutants, while the rhythmicity of the angular velocity was higher for wildtypes. The melatonin production of the mutants showed a weaker rhythmicity, but surprisingly, there were no differences in the rhythmicity of clock-related gene expression between genotypes that could explain a mechanism for GR functionality at the transcriptional level. Furthermore, our results show that grs357 larvae have a more erratic swimming path, and cover more distance during locomotor activity than wild type larvae, in line with previously described behaviour of this mutant. Therefore, these results suggest that GR affects the diel rhythmicity of zebrafish larvae at the behavioural and endocrine level, but that these effects are not mediated by changes in the expression of clock-related genes.

Profound effects of glucocorticoid resistance on anxiety-related behavior in zebrafish adults but not in larvae.

Previously, adult zebrafish with a mutation in the gene encoding the glucocorticoid receptor (Gr) were demonstrated to display anxiety- and depression-like behavior that could be reversed by treatment with antidepressant drugs, suggesting that this model system could be applied to study novel therapeutic strategies against depression. Subsequent studies with zebrafish larvae from this grs357 line and a different gr mutant have not confirmed these effects. To investigate this discrepancy, we have analyzed the anxiety-like behavior in 5 dpf grs357 larvae using a dark/tapping stimulus test and a light/dark preference test. In addition, grs357 adult fish were subjected to an open field test. The results showed that in larvae the mutation mainly affected general locomotor activity (decreased velocity in the dark/tapping stimulus test, increased velocity in the light/dark preference test). However, parameters considered specific readouts for anxiety-like behavior (response to dark/tapping stimulus, time spent in dark zone) were not altered by the mutation. In adults, the mutants displayed a profound increase in anxiety-like behavior (time spent in outer zone in open field test), besides changes in locomotor activity (decreased velocity, increased angular velocity and freezing time). We conclude that the neuronal circuitry involved in anxiety- and depression-like behavior is largely affected by deficient Gr signaling in adult fish but not in larvae, indicating that this circuitry only fully develops after the larval stages in zebrafish. This makes the zebrafish an interesting model to study the ontology of anxiety- and depression-related pathology which results from deficient glucocorticoid signaling.

Polystyrene nanoplastics disrupt glucose metabolism and cortisol levels with a possible link to behavioural changes in larval zebrafish.

Plastic nanoparticles originating from weathering plastic waste are emerging contaminants in aquatic environments, with unknown modes of action in aquatic organisms. Recent studies suggest that internalised nanoplastics may disrupt processes related to energy metabolism. Such disruption can be crucial for organisms during development and may ultimately lead to changes in behaviour. Here, we investigated the link between polystyrene nanoplastic (PSNP)-induced signalling events and behavioural changes. Larval zebrafish exhibited PSNP accumulation in the pancreas, which coincided with a decreased glucose level. By using hyperglycemic and glucocorticoid receptor (Gr) mutant larvae, we demonstrate that the PSNP-induced disruption in glucose homoeostasis coincided with increased cortisol secretion and hyperactivity in challenge phases. Our work sheds new light on a potential mechanism underlying nanoplastics toxicity in fish, suggesting that the adverse effect of PSNPs are at least in part mediated by Gr activation in response to disrupted glucose homeostasis, ultimately leading to aberrant locomotor activity.

Biological clock function is linked to proactive and reactive personality types.

BACKGROUND: Many physiological processes in our body are controlled by the biological clock and show circadian rhythmicity. It is generally accepted that a robust rhythm is a prerequisite for optimal functioning and that a lack of rhythmicity can contribute to the pathogenesis of various diseases. Here, we tested in a heterogeneous laboratory zebrafish population whether and how variation in the rhythmicity of the biological clock is associated with the coping styles of individual animals, as assessed in a behavioural assay to reliably measure this along a continuum between proactive and reactive extremes. RESULTS: Using RNA sequencing on brain samples, we demonstrated a prominent difference in the expression level of genes involved in the biological clock between proactive and reactive individuals. Subsequently, we tested whether this correlation between gene expression and coping style was due to a consistent change in the level of clock gene expression or to a phase shift or to altered amplitude of the circadian rhythm of gene expression. Our data show a remarkable individual variation in amplitude of the clock gene expression rhythms, which was also reflected in the fluctuating concentrations of melatonin and cortisol, and locomotor activity. This variation in rhythmicity showed a strong correlation with the coping style of the individual, ranging from robust rhythms with large amplitudes in proactive fish to a complete absence of rhythmicity in reactive fish. The rhythmicity of the proactive fish decreased when challenged with constant light conditions whereas the rhythmicity of reactive individuals was not altered. CONCLUSION: These results shed new light on the role of the biological clock by demonstrating that large variation in circadian rhythmicity of individuals may occur within populations. The observed correlation between coping style and circadian rhythmicity suggests that the level of rhythmicity forms an integral part of proactive or reactive coping styles.

Conservation physiology of animal migration.

Migration is a widespread phenomenon among many taxa. This complex behaviour enables animals to exploit many temporally productive and spatially discrete habitats to accrue various fitness benefits (e.g. growth, reproduction, predator avoidance). Human activities and global environmental change represent potential threats to migrating animals (from individuals to species), and research is underway to understand mechanisms that control migration and how migration responds to modern challenges. Focusing on behavioural and physiological aspects of migration can help to provide better understanding, management and conservation of migratory populations. Here, we highlight different physiological, behavioural and biomechanical aspects of animal migration that will help us to understand how migratory animals interact with current and future anthropogenic threats. We are in the early stages of a changing planet, and our understanding of how physiology is linked to the persistence of migratory animals is still developing; therefore, we regard the following questions as being central to the conservation physiology of animal migrations. Will climate change influence the energetic costs of migration? Will shifting temperatures change the annual clocks of migrating animals? Will anthropogenic influences have an effect on orientation during migration? Will increased anthropogenic alteration of migration stopover sites/migration corridors affect the stress physiology of migrating animals? Can physiological knowledge be used to identify strategies for facilitating the movement of animals? Our synthesis reveals that given the inherent challenges of migration, additional stressors derived from altered environments (e.g. climate change, physical habitat alteration, light pollution) or interaction with human infrastructure (e.g. wind or hydrokinetic turbines, dams) or activities (e.g. fisheries) could lead to long-term changes to migratory phenotypes. However, uncertainty remains because of the complexity of biological systems, the inherently dynamic nature of the environment and the scale at which many migrations occur and associated threats operate, necessitating improved integration of physiological approaches to the conservation of migratory animals.

Comparison of swimming capacity and energetics of migratory European eel (Anguilla anguilla) and New Zealand short-finned eel (A. australis).

The spawning migration of the European eel (Anguilla anguilla) can cover more than 6000 km, while that of the New Zealand short-finned eel (A. australis) is assumed to be approximately 3000 km. Since these species are expected to show adaptive traits to such an important lifetime event, we hypothesized differences in swimming capacity and energetics as a response to this adaptation. In an experimental swimming respirometer set-up, critical swimming speed (Ucrit), optimal swimming speed (Uopt), mass specific oxygen consumption rate (MO2), standard metabolic rate (SMR), active metabolic rate at Ucrit (AMRcrit) and at Uopt (AMRopt), the minimum cost of transport at Uopt (COTmin), and the scope for activity, were assessed and compared between the species. With a similar body length and mass, European eels showed ca. 25% higher values for both Ucrit and Uopt, and 23% lower values for COTmin, compared to New Zealand short-finned eels. However, SMR, AMRcrit, AMRopt, and scope for activity did not differ between the species, indicating very similar swimming physiology traits. This study discusses physiological aspects of long distance migration and provides recommendations for (a) swimming respirometry in anguilliform fish, and (b) telemetry research using externally attached pop-up tags.

Behavioral changes in response to sound exposure and no spatial avoidance of noisy conditions in captive zebrafish.

Auditory sensitivity in fish serves various important functions, but also makes fish susceptible to noise pollution. Human-generated sounds may affect behavioral patterns of fish, both in natural conditions and in captivity. Fish are often kept for consumption in aquaculture, on display in zoos and hobby aquaria, and for medical sciences in research facilities, but little is known about the impact of ambient sounds in fish tanks. In this study, we conducted two indoor exposure experiments with zebrafish (Danio rerio). The first experiment demonstrated that exposure to moderate sound levels (112 dB re 1 µPa) can affect the swimming behavior of fish by changing group cohesion, swimming speed and swimming height. Effects were brief for both continuous and intermittent noise treatments. In the second experiment, fish could influence exposure to higher sound levels by swimming freely between an artificially noisy fish tank (120-140 dB re 1 µPa) and another with ambient noise levels (89 dB re 1 µPa). Despite initial startle responses, and a brief period in which many individuals in the noisy tank dived down to the bottom, there was no spatial avoidance or noise-dependent tank preference at all. The frequent exchange rate of about 60 fish passages per hour between tanks was not affected by continuous or intermittent exposures. In conclusion, small groups of captive zebrafish were able to detect sounds already at relatively low sound levels and adjust their behavior to it. Relatively high sound levels were at least at the on-set disturbing, but did not lead to spatial avoidance. Further research is needed to show whether zebrafish are not able to avoid noisy areas or just not bothered. Quantitatively, these data are not directly applicable to other fish species or other fish tanks, but they do indicate that sound exposure may affect fish behavior in any captive condition.

Behavioral and physiological indicators of stress coping styles in larval zebrafish.

Different individuals cope with stressors in different ways. Stress coping styles are defined as a coherent set of individual behavioral and physiological differences in the response to a stressor which remain consistent across time and context. In the present study, we have investigated coping styles in larval zebrafish (Danio rerio) at 8 days post-fertilization. Larvae were separated into two groups, according to the emergence sequence from a darkened into a novel well-lit environment, early (EE) and late (LE) emergers. We used brief periods of netting as a stressor. Swimming behavior and kinematics before and after netting stress were analyzed, as were whole-body cortisol levels before and at 10, 30 and 60 min after the stress event. The results show that general swimming activity was different between EE and LE larvae, with lower baseline cumulative distance and more erratic swimming movements in EE than in LE larvae. EE larvae showed a faster recovery to baseline levels after stress than LE larvae. Cortisol baseline levels were not different between EE and LE larvae, but peak levels after stress were higher and the recovery towards basal levels was faster in EE than in LE larvae. This study shows that coping styles are manifest in zebrafish larvae, and that behavior and swimming kinematics are associated with different cortisol responses to stress. A better understanding of the expression of coping styles may be of great value for medical applications, animal welfare issues and conservation.

The effect of drag and attachment site of external tags on swimming eels: experimental quantification and evaluation tool.

Telemetry studies on aquatic animals often use external tags to monitor migration patterns and help to inform conservation effort. However, external tags are known to impair swimming energetics dramatically in a variety of species, including the endangered European eel. Due to their high swimming efficiency, anguilliform swimmers are very susceptibility for added drag. Using an integration of swimming physiology, behaviour and kinematics, we investigated the effect of additional drag and site of externally attached tags on swimming mode and costs. The results show a significant effect of a) attachment site and b) drag on multiple energetic parameters, such as Cost Of Transport (COT), critical swimming speed (Ucrit) and optimal swimming speed (Uopt), possibly due to changes in swimming kinematics. Attachment at 0.125 bl from the tip of the snout is a better choice than at the Centre Of Mass (0.35 bl), as it is the case in current telemetry studies. Quantification of added drag effect on COT and Ucrit show a (limited) correlation, suggesting that the Ucrit test can be used for evaluating external tags for telemetry studies until a certain threshold value. Uopt is not affected by added drag, validating previous findings of telemetry studies. The integrative methodology and the evaluation tool presented here can be used for the design of new studies using external telemetry tags, and the (re-) evaluation of relevant studies on anguilliform swimmers.

Covariation between behaviour and physiology indicators of coping style in zebrafish (Danio rerio).

All vertebrates exhibit physiological responses to a wide variety of stressors. The amplitude and profile of the response depend on the intensity, duration, controllability and predictability of the stressor, but there is also individual variation in the response, termed coping style. A better understanding of the expression of coping styles is of great value for medical applications, animal welfare issues and conservation. Here, we investigated the effect of repeated netting stress on proactive and reactive zebrafish (Danio rerio) as an upcoming model system for stress research. Fish were separated by coping styles according to the order of entering a novel environment. Subsequently, repeated netting stress was applied as stressor, over a period of 21 days. Full-body cortisol levels were determined at 0, 15, 30, 60 and 120 min after the last repeated stress event. Our results show that reactive fish display i) increased basal cortisol concentrations after being repeatedly stressed, ii) higher cortisol secretion over time and iii) slow recovery of cortisol concentration towards basal levels after the last repeated stress event. This study shows for the first time in zebrafish that different coping styles are associated with different cortisol responses during the recovery from stress over time and that coping styles can explain otherwise unaccounted variation in physiological stress responses.

Male European eels are highly efficient long distance swimmers: effects of endurance swimming on maturation.

European eels (Anguilla anguilla) migrate ~6000km towards their spawning area in the Sargasso Sea. Based on the recent discovery that males swim even more efficiently than females, it was predicted that males also would be able to swim ~6000km within six months. Additionally, eels do not mature naturally in captivity due to strong neural inhibition. Earlier, it was hypothesized that swimming exercise is a natural trigger to induce sexual maturation and may even result in full maturation. In the present study two groups of farmed male silver eels were subjected to either endurance swimming or resting for up to 6months. It was found that male eels were able to swim continuously for a total distance of 6670km within 6months. The body weight decrease in swimming and resting males after 6months was similar (<30g) underlining the extreme low energy cost of swimming. In contrast to our expectation long-term swimming did not induce sexual maturation in farmed silver eels, suggesting that swimming alone is not sufficient as a trigger for sexual maturation. In conclusion, male eels are efficient long distance swimmers and likely able to cover the distance to the Sargasso Sea within the expected time span of 6months.

Pop up satellite tags impair swimming performance and energetics of the European eel (Anguilla anguilla).

Pop-up satellite archival tags (PSATs) have recently been applied in attempts to follow the oceanic spawning migration of the European eel. PSATs are quite large, and in all likelihood their hydraulic drag constitutes an additional cost during swimming, which remains to be quantified, as does the potential implication for successful migration. Silver eels (L(T) = 598.6±29 mm SD, N = 9) were subjected to swimming trials in a Steffensen-type swim tunnel at increasing speeds of 0.3-0.9 body lengths s(-1), first without and subsequently with, a scaled down PSAT dummy attached. The tag significantly increased oxygen consumption (MO(2)) during swimming and elevated minimum cost of transport (COT(min)) by 26%. Standard (SMR) and active metabolic rate (AMR) as well as metabolic scope remained unaffected, suggesting that the observed effects were caused by increased drag. Optimal swimming speed (U(opt)) was unchanged, whereas critical swimming speed (U(crit)) decreased significantly. Swimming with a PSAT altered swimming kinematics as verified by significant changes to tail beat frequency (f), body wave speed (v) and Strouhal number (St). The results demonstrate that energy expenditure, swimming performance and efficiency all are significantly affected in migrating eels with external tags.

Optimal swimming speeds reflect preferred swimming speeds of brook charr (Salvelinus fontinalis Mitchill, 1874).

Several measures have been developed to quantify swimming performance to understand various aspects of ecology and behaviour, as well as to help design functional applications for fishways and aquaculture. One of those measures, the optimal swimming speed, is the speed at which the cost of transport (COT) is minimal, where COT is defined as the cost of moving unit mass over unit distance. The experimental protocol to determine the optimal swimming speed involves forced-swimming in a flume or respirometer. In this study, a 4.5-m-long tilted raceway with gradually increasing upstream water speed is used to determine a novel, behaviourally based swimming parameter: the preferred swimming speed. The optimal swimming speed and the preferred swimming speed of brook charr were determined and a comparison of the two reveals that the optimal swimming speed (25.9 ± 4.5 cm s⁻¹ or 1.02 ± 0.47 bl s⁻¹) reflected the preferred swimming speed (between 20 cm s⁻¹ or 0.78 ± 0.02 bl s⁻¹ and 25 cm s⁻¹ or 0.95 ± 0.03 bl s⁻¹). The preferred swimming speed can be advantageous for the determination of swimming speeds for the use in aquaculture studies.

Partition of aerobic and anaerobic swimming costs related to gait transitions in a labriform swimmer.

Members of the family Embiotocidae exhibit a distinct gait transition from exclusively pectoral fin oscillation to combined pectoral and caudal fin propulsion with increasing swimming speed. The pectoral-caudal gait transition occurs at a threshold speed termed U(p-c). The objective of this study was to partition aerobic and anaerobic swimming costs at speeds below and above the U(p-c) in the striped surfperch Embiotoca lateralis using swimming respirometry and video analysis to test the hypothesis that the gait transition marks the switch from aerobic to anaerobic power output. Exercise oxygen consumption rate was measured at 1.4, 1.9 and 2.3 L s(-1). The presence and magnitude of excess post-exercise oxygen consumption (EPOC) were evaluated after each swimming speed. The data demonstrated that 1.4 L s(-1) was below the U(p-c), whereas 1.9 and 2.3 L s(-1) were above the U(p-c). These last two swimming speeds included caudal fin propulsion in a mostly steady and unsteady (burst-assisted) mode, respectively. There was no evidence of EPOC after swimming at 1.4 and 1.9 L s(-1), indicating that the pectoral-caudal gait transition was not a threshold for anaerobic metabolism. At 2.3 L s(-1), E. lateralis switched to an unsteady burst and flap gait. This swimming speed resulted in EPOC, suggesting that anaerobic metabolism constituted 25% of the total costs. Burst activity correlated positively with the magnitude of the EPOC. Collectively, these data indicate that steady axial propulsion does not lead to EPOC whereas transition to burst-assisted swimming above U(p-c) is associated with anaerobic metabolism in this labriform swimmer.

Hormonal and ion regulatory response in three freshwater fish species following waterborne copper exposure.

We evaluated effects of sublethal copper exposure in 3 different freshwater fish: rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio) and gibel carp (Carassius auratus gibelio). In a first experiment we exposed these fishes to an equally toxic Cu dose, a Cu level 10 times lower than their 96 h LC50 value: 20, 65, and 150 microg/L Cu. In a second series we exposed them to the same Cu concentration (50 microg/L). Na+/K+-ATPase activity in gill tissue was disturbed differently in rainbow trout then in common and gibel carp. Rainbow trout showed a thorough disruption of plasma ion levels at the beginning of both exposures, whereas common carp and gibel carp displayed effects only after 3 days. Rainbow trout and common carp thyroid hormones experienced adverse effects in the beginning of the exposure. The involvement of prolactin in handling metal stress was reflected in changes of mRNA prolactin receptor concentrations in gill tissue, with an up regulation of this mRNA in rainbow trout and a down regulation in gibel carp, which was more pronounced in the latter. Overall, rainbow trout appeared more sensitive in the beginning of the exposure, however, when it overcame this first challenge, it handled copper exposure in a better manner then common and gibel carp as they showed more long term impacts of Cu exposure.