Search

Parasites can, in theory, have large impacts on the survival of fish populations. One method to evaluate such impacts on anadromous species is to apply manipulative field experiments in which parallel groups of antiparasitically treated and non-treated fish are simultaneously released and then subsequently recaptured as returning adults. A systematic review and meta-analysis on all such Norwegian studies on Salmo salar provided a data set for the time period 1996 to 2011 on 118 release groups comprising 657 624 fish released and 3989 recaptured. The overall risk ratio ( RR) was estimated to be 1.18 (95% CI: 1.07-1.30). The effect varied strongly between groups, (Higgins I2 = 40.1%). Over 70% of this heterogeneity could be explained by the release location, time period and baseline survival. The most important predictor variable was baseline survival. In groups with low recapture in the control group (low baseline survival), the effect of treatment was high ( RR = 1.7), while in groups with high recapture in the control group (high baseline survival), there was no effect of treatment ( RR ~ 1.00). The most prevalent parasite in the region affected by the drugs administered was Lepeophtheirus salmonis. Hence, the meta-analysis supports the hypothesis that L. salmonis contributes to the mortality of S. salar during outward migration. However, the effect of treatment was not consistent, but was evidently strongly modulated by other risk factors. The results suggest that the population-level effects of parasites cannot be estimated independently of other factors affecting the marine survival of S. salar. [ABSTRACT FROM AUTHOR]

Lice-infected sea trout populations were monitored using fish traps in the Romsdalsfjord (Norway). The reliability and efficiency of this capture technique, which allows estimation of lice infestation rates without killing the fish, was evaluated through a mark–recapture study. A total of 2447 sea trout smolts were captured, tagged and released over a three-year period. There was a considerable variation in capture rates (range: 0.4–17.7 fish per day) and sea lice numbers (number of lice per fish: 2.8–30.3; number of lice per gram body weight: 0.02–0.69) among localities, sampling times and years. Recapture rates of tagged fish with traps, which were low (2% or 0.11 fish per day), showed that the risk for pseudoreplication was minor, in terms of counting lice on the same fish several times. Most of the tagged sea trout (90%) were recaptured within the first two months after release, and no significant variations in lice numbers were found between tagging and recapture. The lack of differences in lice levels between tagging and recapture during the first week after tagging indicated that the method most likely would not significantly underestimate the lice infestations due to loss of lice during handling. Therefore, our results confirm that the use of fish traps is a suitable method for estimation of lice numbers on wild salmonids. [ABSTRACT FROM PUBLISHER]

The effects of 40 mg/L metomidate and 300 mg/L iso-eugenol (i.e. 600 mg/L Aqui- S vet.) anaesthesia on the stress response in European silver eel during a process of complete anaesthesia, recovery and long-term survival were studied. Metomidate is a hypnotic agent with no analgesia, whereas Aqui- S vet. is a true anaesthetic. There was no difference between fish exposed to Aqui- S vet. and metomidate, with respect to time to anaesthesia (mean 3.8 and 2.6 min respectively) and recovery (mean 7.6 and 6.5 min respectively). For the metomidate group, the plasma cortisol concentration increased to a peak during the recovery phase, and was significantly higher than for the Aqui- S vet. group, which showed no such increase. Fish were kept in tanks with seawater for monitoring of long-term survival (4 months) after anaesthesia treatment, and no mortality was observed in either group. The results indicate that metomidate is a potential stressor to European eels during exposure, and we do not recommend using metomidate in this species. Aqui- S vet., however, seems promising as a stress-reducing anaesthetic for European eel, and if used properly could improve animal welfare and survivability during and after common ecology-related procedures, as capture, tagging and size measuring. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Maximum sustained swimming speeds of the European minnow were examined using increased velocity tests in a swim-speed chamber. Maximum sustained swimming speed for the size class 50-64 mm was 10.4 ± 4.0 cm s-1 (mean ± SD), for the size class 65-79 mm 14.2 ± 4.8 cm s-1, and for the size class 80-105 mm 16.0 ± 5.6 cm s-1. Similarly sized minnows were able to maintain considerably higher speeds in a raceway. For instance, individuals of the largest size class could maintain a swimming speed of 34 cm s-1 for at least 25 min. Hence, the maximum swimming capacity of the fish was highly underestimated using the increased velocity test in the swim-speed chamber. The unintentional distribution of minnows by man to new watersheds is considered a critical environmental problem in Norway, because of their potential to develop high densities in communities with low diversity. Recorded high swimming speeds indicated minnows' capability to spread further upstream when introduced to new water systems, and that their swimming and jumping abilities must be taken into account when constructing migration barriers to prevent further spreading. High swimming speeds could also indicate minnows' potential for competing with salmonids not only in lakes but also in riverine environments. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the effect of clove oil (4.0 mg L−1) sedation, compared with non-sedation, on the primary (plasma cortisol), secondary (osmoregulation) and tertiary (mortality) stress responses in Atlantic salmon smolts during transport and transfer to sea. Clove oil sedation during on- and off-loading sufficiently reduced the primary stress response to lower mortality (2.1%) during transfer to sea compared with unsedated fish, which experienced a mortality rate above 12.2%. The unsedated fish experienced an acute mortality that stabilized only 6 days after the transport. None of the secondary stress responses measured in this experiment could contribute towards explaining this phenomenon, with the possible exception of plasma magnesium (Mg2+). Plasma Mg2+ differed between the groups; while plasma Mg2+ in the clove oil sedated group returned to pre-stress levels 72 h after transport, the unsedated group showed no such recovery even 1 week after transport, which may indicate a disturbance in the hydromineral balance, and provides a plausible explanation for the delayed mortality in this group. Eugenol-based anaesthetics appear to be promising as a stress-reducing sedative for Atlantic salmon smolts, and, if used properly, this chemical could improve animal welfare and survivability during and after common aquaculture-related incidents. [ABSTRACT FROM AUTHOR]

Abstract: Disease costs the Norwegian aquaculture industry approximately NOK 1 billion ($ 150000000) every year, and NOK 250000000 ($36000000) is spent on vaccines each year by the industry. Many of the disease outbreaks take place during the first months of transfer to the sea sites. Thus, the aim of this project was to monitor physiological stress parameters as plasma cortisol, glucose and lactate in salmon smolts before and after regular well boat transports. The loading process was observed to be a more severe stressor than the transport itself. Only minor plasma cortisol increases were observed during unloading. In four out of five transports, plasma cortisol had returned to resting level at arrival. However in one, which showed an unusually high mortality rate during the first month after transfer to the sea, the plasma cortisol level remained high during unloading. The study showed that well boat transports seemed to have an important recovery function. Without this ability to recover between the stressors, as on- and unloading, the ability for salmon smolts to handle multiple stressors was reduced. Further, the present study seems to strengthen the fact that some of the increased mortality experienced at sea sites in Norway may be explained by handling and transport prior to deliverance of smolts. Care should be taken during commercial boat transports. Planning of well boat routes, and avoidance of high seas could contribute to minimise mortality experienced after transports. [Copyright &y& Elsevier]

We recorded the observed and actual swimming speeds of Atlantic salmon and sea trout post-smolts in a Norwegian fjord system, and initiated studies on the orientation mechanisms of the post-smolts. We tracked Atlantic salmon and sea trout with acoustic transmitters for up to 14 h after release. The actual swimming speed and direction of a fish relative to the ground is the vector sum of the observed movements of the fish and the movements of the water. We determined actual swimming speeds and directions of the post-smolts, which reflect their real swimming capacities and orientation, by corrections for the speed and direction of the water current. The post-smolts were actively swimming. The observed direction of movement was dependent on the actual movement of the fish and not the water current. Water currents were not systematically used as an orientation cue either in Atlantic salmon or sea trout, as the actual movements were random compared to the direction of the water current. The actual movement of sea trout were in all compass directions, with no systematic pattern. The Atlantic salmon also moved in all compass directions, but with the lowest frequency of actual movement towards the fjord. [ABSTRACT FROM AUTHOR]

We caught smolts of Arctic charr, Salvelinus alpinus (L.), Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in a trap situated at the mouth of the river Halselva (70° N 23° E), northern Norway during a 5-year period. Salmon and charr were the first to leave freshwater at the end of May, while most trout left freshwater about 14 days later. Whereas the midnight sun shines continuously during the downstream migration period, the light intensity has a diel intensity pattern. The majority of the descending migrants were recorded during the night. The number of descending fish was relatively low at water temperatures below 3°C. The increase in water level was largely caused by snowmelt and thus correlated with lower water temperatures. The number of migrants of all three species increased with increasing water level and decreased with increasing water temperature, with the exception of trout, which increased with water temperature. Notably, the increase in number of migrants was also correlated with the increase in water level the following day, indicating that fish movements represent an early response to a later spate. There was no significant relationship between the number of migrants and the daily change in water level or temperature. The three species were highly synchronised in their daily number of migrants. The strongest synchronisation was found between Arctic charr and Atlantic salmon, followed by Arctic charr and brown trout. [ABSTRACT FROM AUTHOR]

One-year-old, hatchery-reared Atlantic salmon (Salmo salar) smolts were Carlin-tagged to test the effects of light sedation and salt water addition during transporting as well as releasing methods on migratory behavior and marine survival in northern Norway. A total of 1600 salmon were tagged for the migratory behavior study in the Halselva River. The fish were transported in water containing either 1 g l−1 metomidate or 11 g l−1 balanced sea salt (Instant Ocean), or a combination of the two. The groups were then allowed to recover for 2 days in net pens in the river, after which they were permitted to migrate freely from the net pens located 1 km upstream from the fish trap. These groups were compared to the untreated groups, which were released directly into the river at the same releasing site at the same time. The results showed that brackish water with metomidate as transport medium, and/or recovery after transport led to improved recaptures of smolts compared to untreated controls. In addition, two groups of approximately 3000 Carlin-tagged Atlantic salmon were transported in 1998 by helicopter from the research station to the nearby Alta River (1-h transport time, including loading) and either released directly into the river or kept in a net pen in the river for 7 days before release. The same releases were performed in 1999. Recaptures of adult salmon in the Alta River were 0.43% and 1.43% (1998 releases) and 1.23% and 1.89% (1999 releases) for smolts released either directly or allowed 7 days to recover in the river before release, respectively. These results shows that the use of stress-reducing methods, especially recovery after transport, can improve both the migratory behavior and marine survival of smolt releases. [Copyright &y& Elsevier]

During peak smoltification, the interactive effects of cortisol and ambient seawater challenge were compared in two strains of Atlantic salmon (Salmo salar) smolts: a domesticated strain, AquaGen and a native River Imsa strain. Tissue and blood samples were taken from untreated fish on 20 May. Fish were then transferred to experimental tanks, allowed to recover for 24 h and cortisol (50 mg kg body mass−1), dissolved in vegetable oil, or vegetable oil alone (sham) was implanted. Samples were taken 5 days post implantation. Fish were then exposed to 24 h ambient seawater challenge (FW–SW) or freshwater to freshwater replacement (FW–FW) and sampled as before. Sham implantation had no significant impact on any of the measured parameters. Cortisol implantation significantly elevated plasma cortisol in FW–FW Imsa smolts, while no effect was observed in FW–SW Imsa smolts. Cortisol implantation had no effect on the plasma cortisol levels of AquaGen smolts regardless of FW–SW challenge. Increased plasma cortisol corresponded with significantly higher plasma glucose levels in FW–FW Imsa smolts. Plasma Na+ and Cl− levels were not affected by cortisol implantation but were significantly increased in FW–SW smolts of both strains. Gill Na+,K+-ATPase activity increased in response to cortisol implantation in only FW–FW smolts but not FW–SW smolts. Gill Na+,K+-ATPase α-subunit mRNA levels were not affected by strain, cortisol injection or transfer protocol, while both CFTR I and CFTR II mRNA levels were significantly higher in AquaGen versus Imsa smolts regardless of treatment. CFTR I mRNA was elevated following cortisol implantation in FW–FW smolts from both strains suggesting CFTR I expression is under the control of cortisol. These findings also suggest that plasma cortisol levels are regulated differently between strains and that cortisol implantation and ambient FW–SW challenge interact, interfering with the individual effects of each of these factors. [Copyright &y& Elsevier]

Two strains of Atlantic salmon (Salmo salar) presmolts were exposed for 3 months to moderately acidic water (pH 5.8; 6±2 μg aluminum (Ali) l−1 inorganic monomeric aluminum-acid exposure group) or non-acid water (pH>6.5–6.9; <5 μg Ali l−1—Good/control group) at NINA Research Station, Ims, Southern Norway. Exposure to low concentrations of Ali raised the gill-aluminum (gill-Al) concentration by 20–30 μg Al g−1 gill dry weight compared to control fish having <10 μg Al g−1 gill dry weight. The fish responded to the Al loading with elevated blood glucose, but retained more normal hematocrit and plasma chloride levels. Fish exposed under acid conditions grew significantly poorer than the control fish. After 3 months of exposure, 150 Carlin-tagged smolts from both Imsa treatments were released into the non-acidic River Imsa, 800 m upstream from a trap that caught all migrating smolts. Acid-exposed fish migrated downstream slightly later than the controls. At the same time, Carlin-tagged fish from all four treatments (Acid and Good, both strains; approximately 1000 fish group−1) were released downstream of the trap located 150 m above the river mouth. Based on the number of adult recaptures (by May 2001), marine survival was 20–30% lower for the acid-exposed fish than for the controls. There were no differences in marine growth between the treatments. The results suggest that even very low concentrations of Ali (6±2 μg l−1) can reduce seawater survival, thereby having effect on the population level. The physiological responses, reduced growth and reduced marine survival also suggest that the presmolts did not acclimate to the acid conditions. [Copyright &y& Elsevier]

Atlantic salmon (Salmo salar L.) smolts (45 g) in freshwater (5.4 °C) were exposed to water containing different concentrations of metomidate from 0 to 10 mg l−1, clove oil (eugenol), Aqui-S™ (iso-eugenol) and Benzoak® (benzocaine) from 0 to 100 mg l−1. All anaesthetic concentrations were mixed and expressed as mg l−1 in relation to the active substance of the various anaesthetics. Metomidate, clove oil, Aqui-S™ and Benzoak® were effective as anaesthetics for Atlantic salmon smolts at concentrations ≥2 mg l−1 (metomidate) and ≥30 mg l−1 (clove oil, Aqui-S®, Benzoak®). The fish entered behavioural stage 4 (failure to respond to external stimuli) within 6.2–2.2 min for metomidate concentrations from 2 to 10 mg l−1, within 8.1–2.2 min (clove oil and Aqui-S™) and 17.4–3.0 min (Benzoak®) for concentrations from 30 to 100 mg l−1. A concentration of 100 mg l−1 of Benzoak®, clove oil and Aqui-S™ caused the salmon smolts to enter stage 5 (arrested opercular activity) after 6.4 and 12 min of exposure, respectively. Metomidate solutions ≥2 mg l−1, clove oil and Aqui-S™ solutions ≥20 mg l−1 prevented plasma cortisol elevation above resting level. Benzoak® (regardless of dosage) did not prevent plasma cortisol elevations above resting level. While the anaesthetics increased mean plasma lactate concentration significantly in nearly all experimental groups, no such changes in plasma glucose were evident in any of the experimental groups. The eugenol-based anaesthetics (clove oil and Aqui-S™) show promise to become effective anaesthetics, with good efficacy at low dosages and with stress-reducing capabilities. They are also inexpensive and easily obtained, and are organic substances safe for both environment and user. [Copyright &y& Elsevier]

Examines whether the process of artificial selection of Atlantic salmon that has resulted in higher growth rate resulted in underlying changes in the insulin-like growth factor I axis of endocrine growth regulation. Correlation of pituitary growth hormone (GH) content with growth rate; Observation of higher plasma GH levels in domesticated fish.

Fish tagging methods are important tools in the research and management of salmonids; the Carlin tag is widely used, especially in anadromous salmonids. However, this tagging method may interfere with fish behaviour and increase post-smolt mortality. To estimate Carlin-tag-inflicted mortality in Arctic charr, we used jet injection of alcian blue (colour tags) as a control. Recapture rates were higher for the colour-tagged fish than for the Carlin-tagged fish for both one- and two-year-old smolts. For one-year-old smolts in 1992, the recapture rate was 18.9% for colour-tagged fish and 10.0% for Carlin-tagged ones. For two-year-old smolts in the same year, 34.0% of colour- and 28.6% of Carlin-tagged fish were recaptured; in 1993, recapture rates were 17.2% and 6.3% for colour- and Carlin-tagged fish, respectively. Colour-tagged one-year-old Arctic charr also grew faster than their Carlin-tagged counterparts. No differences in growth rates were found between tagging methods in two-year-olds. These results imply that for hatchery-reared Arctic charr, survival rates using Carlin tagging may be half to one third that of colour tagging. Growth was also higher among colour-tagged fish, indicating that Carlin tags alter the behaviour of fish in the sea. [ABSTRACT FROM AUTHOR]

The abundance of salmon lice was examined in two stocks of sympatric anadromous Arctic char and sea trout in sub-Arctic regions in northern Norway in June, July, and August 1992 and 1993. One stock feeds in a coastal area exposed to moderate salmon farming activity (exposed area), while the other feed in a region without salmon farms (unexposed area). The salmon lice infestation on both species differed significantly between the exposed and unexposed area as well as between years and also between weeks within the same year. We did not detect, however, any clear significant differences in salmon lice abundance between sympatric populations of Arctic char and sea trout, or between different size groups of the species. The 1992 and 1993 infestation pattern in the exposed area showed an epidemic tendency in both Arctic char and sea trout, characterised by a sudden increase in both prevalence and abundance of lice larvae in July 1992 (23.6±25.7 lice/fish) and August 1993 (19.9±20.8 lice/fish). We therefore suggest that salmon lice epidemics, previously only observed on sea trout, may also occur in populations of Arctic char, and that fish farming contributes to the elevated lice level in wild fish. The fish in the unexposed area were also infested, although at significantly lower levels than fish from the exposed area. The infestation peaked in August 1992 at 13.0±18.1 lice/fish and August 1993 at 3.9±4.5 lice/fish, suggested that lice originating on ascending wild Atlantic salmon, or lice larvae drifting from farming areas, may infest Arctic char and sea trout also in unexposed localities in Subarctic areas. [Copyright &y& Elsevier]

Investigates the mechanisms underlying the differences in seawater tolerance and gene expression in two strains of Atlantic salmon smolts. Plasma ions in seawater exposures; Gill sodium, potassium-adenosine triphosphatase activity; Gill messenger RNA abundance; Effect of freshwater replacement on plasma ion levels between strains.

• Sustainability indicators determine what sustainable aquaculture has come to be. • Aquaculture certification schemes promote a skewed understanding of sustainability. • The schemes mainly emphasize issues related to environmental and governance issues. • Working towards sustainability requires a holistic perspective. Sustainability certification has become an increasingly important feature in aquaculture production, leading to a multitude of schemes with various criteria. However, the large number of schemes and the complexity of the standards creates confusion with respect to which sustainability objectives are targeted. As a result, what is meant by 'sustainability' is unclear. In this paper, we examine the operationalisation of the concept from the vantage point of the certifying authorities, who devise standards and grant or withhold certification of compliance. We map the criteria of eight widely-used certification schemes using the four domains of the Wheel of Sustainability, a reference model designed to encompass a comprehensive understanding of sustainability. We show that, overall, the sustainability certifications have an overwhelming focus on environmental and governance indicators, and only display scattered attempts at addressing cultural and economic issues. The strong focus on governance indicators is, to a large degree, due to their role in implementing and legitimising the environmental indicators. The strong bias implies that these certification schemes predominantly focus on the environmental domain and do not address sustainability as a whole, nor do they complement each other. Sustainability is by definition and by necessity a comprehensive concept, but if the cultural and economic issues are to be addressed in aquaculture, the scope of certification schemes must be expanded. The Wheel of Sustainability can serve as a valid lexicon and asset to guide such efforts. [ABSTRACT FROM AUTHOR]

Monitoring stress levels of farmed Atlantic salmon (Salmo salar) is important to ensure fish welfare and optimize farm operations. Feces could be a promising matrix for assessing stress responses in fish, based on their properties of low-invasive sampling and allowing repeated sampling over time. Meanwhile, elevated levels of cortisol metabolites (CMs) in feces indicate the increases in plasma cortisol levels (PLA) after exposure to acute stress. However, the dynamics of fecal CMs following acute stress in Atlantic salmon remain unclear. In this study, a confinement stress involving chasing and crowding was conducted to investigate the responses of gastrointestinal CMs to an acute stressor in Atlantic salmon. The post-smolts, with an average weight of 155.21 g, were sampled before and at 30 min, 1.5, 6, 12, 18, 24, 36, and 48 h after the onset of stress. Blood and gastrointestinal contents from the stomach, proximal intestine, and distal intestine of each fish were collected and subsequently analyzed, using competitive enzyme-linked immunosorbent assay (ELISA). The results demonstrated that the pre-stress level of PLA was low (4.28 ± 6.13 ng/ml) and reached a peak within 30 min following stress. The levels of CMs in gastrointestinal contents from stomach (SCMs), proximal intestine (PCMs), and distal intestine (DCMs) in pre-stress group were 0.82 ± 0.50, 18.31 ± 6.14 and 16.04 ± 6.69 ng/g, respectively. Gastrointestinal CMs increased significantly within 30 min and the peak levels of SCMs (3.51 ± 3.75 ng/g), PCMs (68.19 ± 23.71 ng/g) and DCMs (65.67 ± 23.37 ng/g) were found at 1.5 h post-stress. The significant increases in PCMs and DCMs post-stress validate the biological relevance of measuring intestinal CMs for assessing acute stress responses in Atlantic salmon. No significant difference was noted between PCMs and DCMs across all samples, suggesting that intestinal contents can serve as a suitable matrix compared with feces when measuring the responses of CMs to acute stress. The time lag between the peak of PLA levels and their reflection in the intestinal contents exceeded 1 h, indicating that using intestinal contents as a matrix to assess stress levels in fish can extend and delay the sampling window. This study highlights valuable guidance for determining the optimal times to utilize intestinal contents for measuring stress responses, providing further insights into the dynamics of fecal CM following acute stress. • Significant differences were not found between cortisol metabolites in proximal (PCMs) and distal intestine (DCMs). • PCMs and DCMs exhibited a similar pattern of variation as plasma cortisol (PLA) in response to acute stress. • Over 1-h delay was detected between the peak of PLA and its reflection in the intestinal content. • The results verify the biological relevance of measuring intestinal cortisol metabolites levels to assess stress responses. [ABSTRACT FROM AUTHOR]

The timing of seaward migration is a key life‐history trait for many anadromous fish species, with growth and survival at sea depending on a match/mismatch scenario between the timing of the sea entry and optimal conditions. Based on a 25‐year study with 15,226 individually tagged brown trout (Salmo trutta) in a Norwegian river, we analysed how the within‐season timing of sea migration impacted growth and survival. In both first‐time and veteran migrants, marine growth was highest for early migrating individuals, large individuals, and those with a low condition factor when entering the sea. Survival was highest for individuals entering the sea early in the season. In first‐time migrants, survival increased with body length. Survival also increased with the number of other smolts migrating simultaneously. As the early smolts were the most successful, it may seem strange that many smolts migrate later in the season. We suggest that late‐migrating smolts may not be of a size and/or physiological state suitable for early marine conditions, and may make the best of a bad situation. [ABSTRACT FROM AUTHOR]

Parasites may have large effects on host population dynamics, marine fisheries and conservation, but a clear elucidation of their impact is limited by a lack of ecosystem-scale experimental data. We conducted a meta-analysis of replicated manipulative field experiments concerning the influence of parasitism by crustaceans on the marine survival of Atlantic salmon (Salmo salar L.). The data include 24 trials in which tagged smolts (totalling 283 347 fish; 1996 -- 2008) were released as paired control and parasiticide-treated groups into 10 areas of Ireland and Norway. All experimental fish were infection-free when released into freshwater, and a proportion of each group was recovered as adult recruits returning to coastal waters 1 or more years later. Treatment had a significant positive effect on survival to recruitment, with an overall effect size (odds ratio) of 1.29 that corresponds to an estimated loss of 39 per cent (95% CI: 18 -- 55%) of adult salmon recruitment. The parasitic crustaceans were probably acquired during early marine migration in areas that host large aquaculture populations of domesticated salmon, which elevate local abundances of ectoparasitic copepods -- particularly Lepeophtheirus salmonis. These results provide experimental evidence from a large marine ecosystem that parasites can have large impacts on fish recruitment, fisheries and conservation. [ABSTRACT FROM AUTHOR]