Wild Salmonids Research Articles

Area protection may reduce salmon louse infection risk to wild salmonids

The Norwegian Institute for Nature Research Nofima Marine IMR Statkraft Energi, Norway European Commission Contract

Epidemiological aspects of viral haemorrhagic septicaemia virus genotype II isolated from Baltic herring, Clupea harengus membras L.

This study was carried out to clarify the role of wild fish, especially Baltic herring, Clupea harengus membras L., in the epidemiology of viral haemorrhagic septicaemia virus (VHSV) in brackish water in Finland. Baltic herring with no visible signs of disease were collected from the Archipelago Sea, the Gulf of Bothnia and the eastern Gulf of Finland. In total, 7580 herring were examined by virus isolation as 758 pooled samples and 3029 wild salmonid broodfish as pooled samples during 2004-2006. VHSV was isolated from 51 pooled herring samples in bluegill fibroblast-2 cells, but not in epithelioma papulosum cyprini cells. The majority of isolations were from the coastal archipelago and from fish caught during the spawning season. Based on glycoprotein (G) gene sequences, the virus was classified as a member of genotype II of VHSV. Pairwise comparisons of the G gene regions of herring isolates revealed that all the isolates were closely related, with 98.8-100% nucleotide homology. Phylogenetic analyses revealed that they were closely related to the strains isolated previously from herring and sprat, Sprattus sprattus (L.), in Gotland and to the VHSV isolates from European river lamprey, Lampetra fluviatilis (L.), in the rivers that flow into the Bothnian Bay. The infection in Baltic herring is likely to be independent of the VHSV Id epidemic in farmed rainbow trout, Oncorhynchus mykiss (Walbaum).

Factors influencing density, distribution, and mesohabitat selection of juvenile wild salmonids and residual hatchery winter steelhead

To best manage Eagle Creek National Fish Hatchery, negative interactions between hatchery salmonids and Endangered Species Act listed wild salmonids in the Eagle Creek Basin need to be minimized. Our objectives were: 1) to compare summer rearing densities in two similar streams, where one stream received a release of hatchery salmonids and one stream did not receive a release of hatchery salmonids, 2) to determine if residual hatchery winter steelhead were present in the Eagle Creek Basin, and 3) if so, determine how their presence and density relates to mesohabitat selection and distribution of naturally produced salmonids. A comprehensive snorkel survey identified significantly higher densities of juvenile coho salmon rearing in North Fork Eagle Creek, compared to upper and lower Eagle Creek. We found age 0 winter steelhead in significantly higher densities in upper Eagle Creek as opposed to lower Eagle Creek and North Fork Eagle Creek. Residual hatchery steelhead were located only in Eagle Creek and were rearing in the same 15 mesohabitat units that contained the estimated majority of wild fish populations. In Eagle Creek, the probability of occurrence for all species, regardless of origin, was highest in the vicinity of the hatchery. Residual hatchery winter steelhead density indicated a negative relationship with age 0 winter steelhead density. Due to residual hatchery winter steelhead being present in only 15 sampled habitat units we recommend future sampling effort be focused in areas with known populations of residual hatchery winter steelhead to determine if a distinct relationship between these population densities exists. From these data it is unclear if residual hatchery steelhead are affecting densities, distributions, and mesohabitat selection of wild salmonids in the basin. However, while we were unable to detect any direct impacts of residual hatchery fish on the wild population, these results do suggest the potential exists for competitive ecological interactions between hatchery and wild populations.

Predation by hatchery yearling salmonids on wild subyearling salmonids in the freshwater environment: A review of studies, two case histories, and implications for management

We conducted a literature review on predation by hatchery yearling salmonids on wild subyearling salmonids in the western United States. The review included 14 studies from the Pacific Northwest and California. In most instances, predation by hatchery yearling salmonids on wild subyearling salmonids occurred at low levels. However, when multiple factors contributing to the incidence of predation were met, localized areas of heavy predation were noted. Total prey consumed ranged from 456 to 111 000 subyearlings for the few studies in which enough information was gathered to make the estimate. We examined two of these studies in more detail: one detecting relatively low predation in four western Washington rivers and one detecting relatively high predation in the Trinity River in northern California. In the case of the rivers in western Washington, over 70% of wild subyearlings had migrated by the time hatchery steelhead were planted and those remaining had grown large enough to reduce their vulnerability to predation. In the case of the Trinity River, less than 20% of wild subyearlings had migrated by the time hatchery steelhead were planted and most were small enough to remain highly vulnerable to predation. We found that managers can effectively minimize the predation rate of hatchery yearling salmonids by reducing the spatial or temporal overlap of predator and prey. Unknown is the extent to which low predation rates, which likely occur in most places hatchery yearlings are released, might still negatively impact prey populations that are at low abundance because of other anthropogenic factors.

Densities of planktonic Lepeophtheirus salmonis before and after an Atlantic salmon farm relocation

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 1:225-232 (2011) - DOI: https://doi.org/10.3354/aei00022 Densities of planktonic Lepeophtheirus salmonis before and after an Atlantic salmon farm relocation Michael J. Penston*, Alastair J. A. McBeath, Colin P. Millar Marine Scotland Science, Marine Laboratory, PO Box 101, 375 Victoria Road, Aberdeen AB11 9DB, UK *Email: m.penston@marlab.ac.uk ABSTRACT: Relocating Atlantic salmon Salmo salar L. farms away from important salmonid rivers is possibly a means to reduce Lepeophtheirus salmonis (Krøyer, 1837) interactions between farmed Atlantic salmon and wild salmonids. However, to date, no data have been presented on the consequences of salmon farm relocation in terms of densities of planktonic L. salmonis. Near-surface plankton were sampled at 5 stations during 2 full farming production cycles; 1 before and 1 after a salmon farm relocation within a sea loch/fjord. The relocation comprised the removal of a salmon farm and the reallocation of its fish biomass to a different farm within the same management area. Over 85% of the larval sea lice we identified in sub-samples were L. salmonis; we therefore assumed that the majority of the larvae found were of that species. Densities of L. salmonis larvae increased significantly at all stations post relocation, except at the station near the vacated farm site where mean densities of nauplii were significantly lower and mean densities of copepodids were lower without statistical ­significance. The removal/relocation of the salmon farm significantly reduced the production of L. salmonis larvae, but did not significantly reduce the infection pressure, as represented by densities of the infectious copepodid stage, at the vacated farm site. This finding indicates that planktonic L. salmonis were transported to the vacated farm site from sources at a minimum of 5 to 8 km distant. KEY WORDS: Scotland · Sea lice · Relocation · Management · Salmon aquaculture · Sea trout Full text in pdf format PreviousNextCite this article as: Penston MJ, McBeath AJA, Millar CP (2011) Densities of planktonic Lepeophtheirus salmonis before and after an Atlantic salmon farm relocation. Aquacult Environ Interact 1:225-232. https://doi.org/10.3354/aei00022 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 1, No. 3. Online publication date: April 15, 2011 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2011 Inter-Research.

Population genetic structure of the parasitic copepod Lepeophtheirus salmonis throughout the Atlantic

The parasitic copepod Lepeophtheirus salmonis is responsible for huge economic losses in the salmonid aquaculture industry, and has been linked with declines of wild salmonid popu - lations. In order to elucidate population genetic structure throughout the Atlantic Ocean, 2495 lice representing 27 samples collected from 22 locations were analysed for 14 microsatellite loci. Signifi- cant overall genetic variation was observed (14 loci: global FST = 0.0057, p < 0.0001), although this decreased slightly when an outlier locus (LsalSTA3), detected as a candidate for positive selection, was removed (13 neutral loci: global FST = 0.0022, p < 0.0001). A relationship between physical and genetic distance was observed (R 2 = 0.179, p = 0.0013), but only when data from LsalSTA3 was included. No overall genetic variation was observed among the 19 samples collected in Norway (Nor- wegian global FST < 0.0001, p = 0.6). None of the within-country (Canada, Ireland, Shetland and Faroe Islands) pairwise FST values were statistically significant when analysing the 13 neutral loci and following Bonferroni correction. Samples taken at 5 Norwegian farms did not exhibit signif- icant genetic differences before and after medicated treatment. We conclude that L. salmonis displays weak but nevertheless statistically significant population genetic variation throughout the Atlantic. Analysis of temporal samples, potentially combined with larger numbers of markers giving greater genome coverage, will be required to fully elucidate the biological significance of the observed variation.

Reduced reproductive success of hatchery coho salmon in the wild: insights into most likely mechanisms

Supplementation of wild salmonids with captive-bred fish is a common practice for both commercial and conservation purposes. However, evidence for lower fitness of captive-reared fish relative to wild fish has accumulated in recent years, diminishing the apparent effectiveness of supplementation as a management tool. To date, the mechanism(s) responsible for these fitness declines remain unknown. In this study, we showed with molecular parentage analysis that hatchery coho salmon (Oncorhynchus kisutch) had lower reproductive success than wild fish once they reproduced in the wild. This effect was more pronounced in males than in same-aged females. Hatchery spawned fish that were released as unfed fry (age 0), as well as hatchery fish raised for one year in the hatchery (released as smolts, age 1), both experienced lower lifetime reproductive success (RS) than wild fish. However, the subset of hatchery males that returned as 2-year olds (jacks) did not exhibit the same fitness decrease as males that returned as 3-year olds. Thus, we report three lines of evidence pointing to the absence of sexual selection in the hatchery as a contributing mechanism for fitness declines of hatchery fish in the wild: (i) hatchery fish released as unfed fry that survived to adulthood still had low RS relative to wild fish, (ii) age-3 male hatchery fish consistently showed a lower relative RS than female hatchery fish (suggesting a role for sexual selection), and (iii) age-2 jacks, which use a sneaker mating strategy, did not show the same declines as 3-year olds, which compete differently for females (again, implicating sexual selection).

Real-time PCR detection of Parvicapsula pseudobranchicola (Myxozoa: Myxosporea) in wild salmonids in Norway

The myxozoan genus Parvicapsula contains 14 species infecting fish, some of which are known to cause severe disease in farmed and wild salmonids. Parvicapsula pseudobranchicola infections were first reported from seawater-reared Atlantic salmon, Salmo salar, in Norway in 2002 and have since then been an increasing problem. The present study describes a Taqman real-time PCR assay for specific detection of P. pseudobranchicola. The Taqman assay targets the 18S rRNA gene of P. pseudobranchicola and is able to detect as few as ten copies of the target sequence. Using the described assay, P. pseudobranchicola was detected in both farmed and wild salmonids, indicating that wild Atlantic salmon, sea trout, Salmo trutta, and Arctic char, Salvelinus alpinus, may be natural hosts of the parasite. Parvicapsula pseudobranchicola was found in samples from wild salmonids in the far south and the far north of Norway, displaying a wide geographic range of the parasite. Farmed salmonids showed P. pseudobranchicola infection levels many folds higher than that observed for wild sea trout, indicating that farmed Atlantic salmon are subjected to an elevated infection pressure compared with wild salmonids.

The application of epidemiology in aquatic animal health -opportunities and challenges.

Over recent years the growth in aquaculture, accompanied by the emergence of new and transboundary diseases, has stimulated epidemiological studies of aquatic animal diseases. Great potential exists for both observational and theoretical approaches to investigate the processes driving emergence but, to date, compared to terrestrial systems, relatively few studies exist in aquatic animals. Research using risk methods has assessed routes of introduction of aquatic animal pathogens to facilitate safe trade (e.g. import risk analyses) and support biosecurity. Epidemiological studies of risk factors for disease in aquaculture (most notably Atlantic salmon farming) have effectively supported control measures. Methods developed for terrestrial livestock diseases (e.g. risk-based surveillance) could improve the capacity of aquatic animal surveillance systems to detect disease incursions and emergence. The study of disease in wild populations presents many challenges and the judicious use of theoretical models offers some solutions. Models, parameterised from observational studies of host pathogen interactions, have been used to extrapolate estimates of impacts on the individual to the population level. These have proved effective in estimating the likely impact of parasite infections on wild salmonid populations in Switzerland and Canada (where the importance of farmed salmon as a reservoir of infection was investigated). A lack of data is often the key constraint in the application of new approaches to surveillance and modelling. The need for epidemiological approaches to protect aquatic animal health will inevitably increase in the face of the combined challenges of climate change, increasing anthropogenic pressures, limited water sources and the growth in aquaculture.Table of contents1 Introduction 42 The development of aquatic epidemiology 73 Transboundary and emerging diseases 93.1 Import risk analysis (IRA) 103.2 Aquaculture and disease emergence 113.3 Climate change and disease emergence 133.4 Outbreak investigations 134 Surveillance and surveys 154.1 Investigation of disease prevalence 154.2 Developments in surveillance methodology 164.2.1 Risk-based surveillance and scenario tree modelling 164.2.2 Spatial and temporal analysis 164.3 Test validation 175 Spread, establishment and impact of pathogens 185.1 Identifying routes of spread 185.1.1 Ex-ante studies of disease spread 195.1.2 Ex-post observational studies 215.2 Identifying risk factors for disease establishment 235.3 Assessing impact at the population level 245.3.1 Recording mortality 245.3.2 Farm health and production records 265.3.3 Assessing the impact of disease in wild populations 276 Conclusions 317 Competing interests 328 Authors' contributions 329 Acknowledgements 3310 References 33

Evidence of farm-induced parasite infestations on wild juvenile salmon in multiple regions of coastal British Columbia, Canada

Salmon farms are spatially concentrated reservoirs of fish host populations that can disrupt natural salmonid host–parasite dynamics. Sea lice frequently infect farm salmon and parasitize sympatric wild juvenile salmonids, with negative impacts on survival in Europe and Pacific Canada. We examined louse parasitism of wild juvenile chum salmon ( Oncorhynchus keta ) and pink salmon ( Oncorhynchus gorbuscha ) from three salmon farming regions in British Columbia (Finlayson, Broughton Archipelago, and Georgia Strait). We compared sites of low and high exposure to farms and included an area without farms (Bella Bella) to assess baseline infection levels. Louse prevalence and abundance were lowest and most similar to natural baseline levels at low-exposure sites and highest at high-exposure sites in all farm regions. A significantly greater proportion of the lice were Lepeophtheirus salmonis at high-exposure sites. Exposure to salmon farms was the only consistently significant factor to explain the variation in prevalence data, with a secondary role played by salinity. Our results support the hypothesis that salmon farms are a major source of sea lice on juvenile wild salmon in salmon farming regions and underscore the importance of using management techniques that mitigate threats to wild stocks.

Salmon lice-induced mortality of Atlantic salmon postsmolts experiencing episodic acidification and recovery in freshwater

Acid rain has reduced several salmonid stocks in Norway and salmon lice have been identified as a major population regulation factor. The combination of these two factors has also been seen to reduce postsmolt survival. In the present study, we have addressed the effects of an episodic exposure to acidic water and later recovery in good freshwater quality (Acid/Recovery groups) followed by salmon lice infestation in seawater in more detail. The ecological perspective of this can be directly addressed to changes over the last decades from chronic acidification over Norway and Europe, to more episodic spring acidification of rivers prior to or during downstream migration of smolts. The results showed that salmon lice-induced mortality increased in all episodic Acid/Rec groups. However, the group given the longest recovery period experienced the lowest mortality compared to the other treatment groups. A period of recovery after acid exposure may eventually restore the fish back to normal physiological level, but in the present experiment a period of 14days of recovery after a 2day exposure to acid water was too short to fully restore the fish back to normal levels. Even short-time episodic acidification followed by recovery during springtime and the vulnerable smoltification process, may therefore have negative and often unnoticed effects in wild salmonids until the postsmolts meet other stressors in the marine phase such as salmon lice and other fish diseases.

Salmon jumping: behavior, kinematics and optimal conditions, with possible implications for fish passageway design

Behavioral and kinematic properties and capacities of wild migratory salmonid fishes swimming upstream and jumping up waterfalls generally have played only minor roles in the design and construction of passageways intended to help these fishes get past dams and other human-made obstacles blocking their movements. This paper reports the results of an experimental study of relevant behavioral and kinematic properties of adult kokanee salmon (Oncorhynchus nerka) jumping up waterfalls as they migrate upstream. We used a portable, adjustable apparatus to study in the field fish responding to artificial waterfalls under a range of flow conditions. We observed fish under conditions of varying water flow rates, pool depths, fall heights and fall angles. We analyzed digital video recordings of their behaviors. Kokanee salmon spontaneously jump up waterfalls within a relatively narrow range of conditions, including low flow speeds, near vertical angles and pool depth to fall height ratios near 1.0. Preferred values for each parameter are, to some extent, dependent on other parameters. In contrast to previous misconceptions, jumping behavior is initiated by running S-start accelerations from beneath the boils formed in the plunge pools below waterfalls, as opposed to C-start standing jumps from the surface. S-starts are immediately followed by burst swimming to the point of takeoff at the surface. These results can contribute to an improved basis for developing designs of fish passageways that may ultimately make them more effective and efficient.

Color Photographic Index of Fall Chinook Salmon Embryonic Development and Accumulated Thermal Units

BackgroundKnowledge of the relationship between accumulated thermal units and developmental stages of Chinook salmon embryos can be used to determine the approximate date of egg fertilization in natural redds, thus providing insight into oviposition timing of wild salmonids. However, few studies have documented time to different developmental stages of embryonic Chinook salmon and no reference color photographs are available. The objectives of this study were to construct an index relating developmental stages of hatchery-reared fall Chinook salmon embryos to time and temperature (e.g., degree days) and provide high-quality color photographs of each identified developmental stage.Methodology/Principal FindingsFall Chinook salmon eggs were fertilized in a hatchery environment and sampled approximately every 72 h post-fertilization until 50% hatch. Known embryonic developmental features described for sockeye salmon were used to describe development of Chinook salmon embryos. A thermal sums model was used to describe the relationship between embryonic development rate and water temperature. Mean water temperature was 8.0°C (range; 3.9–11.7°C) during the study period. Nineteen stages of embryonic development were identified for fall Chinook salmon; two stages in the cleavage phase, one stage in the gastrulation phase, and sixteen stages in the organogenesis phase. The thermal sums model used in this study provided similar estimates of fall Chinook salmon embryonic development rate in water temperatures varying from 3.9–11.7°C (mean = 8°C) to those from several other studies rearing embryos in constant 8°C water temperature.Conclusions/SignificanceThe developmental index provides a reasonable description of timing to known developmental stages of Chinook salmon embryos and was useful in determining developmental stages of wild fall Chinook salmon embryos excavated from redds in the Columbia River. This index should prove useful to other researchers who wish to approximate fertilization dates of Chinook salmon eggs from natural redds, assuming the thermal history of embryos is known.

Erratum

Journal of Fish DiseasesVolume 33, Issue 7 p. 623-623 Free Access Erratum This article corrects the following: Molecular differentiation of infectious pancreatic necrosis virus isolates from farmed and wild salmonids in Ireland N M Ruane, L J McCarthy, D Swords, K Henshilwood, Volume 32Issue 12Journal of Fish Diseases pages: 979-987 First Published online: July 10, 2009 First published: 09 June 2010 https://doi.org/10.1111/j.1365-2761.2010.01166_1.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Molecular differentiation of infectious pancreatic necrosis virus isolates from farmed and wild salmonids in Ireland N M Ruane, L J McCarthy, D Swords and K Henshilwood.1 Published article online: 10 July 2009; doi: 10.1111/j.1365-2761.2009.01080.x The copyright line for this article was presented in error as © 2009 Marine Institute. Amoebic gill disease resistance is not related to the systemic antibody response of Atlantic salm, Salmo salar L. R S Taylor, P B Crosbie, M T Cook.2 Published article online: 26 November 2009; doi: 10.1111/j.1365-2761.2009.01108.x The copyright line for this article was presented in error as © 2009 CSIRO Marine & Atmospheric Research. Prospective longitudinal studies of salmonid alphavirus infections on two Atlantic salmon farms in Ireland; evidence for viral persistence D A Graham, E Fringuelli, C Wilson, H M Rowley, A Brown, H Rodger, M F McLoughlin, C McManus, E Casey, L J McCarthy, N M Ruane.3 Published article online: 30 August 2009; doi: 10.1111/j.1365-2761.2009.01096.x The copyright line for this article was presented in error as © 2009 Agri-food & Biosciences Institute. In the above articles, the copyright line should have been printed as © 2009 Blackwell Publishing Ltd. The publishers apologize for this error. References Ruane N.M., McCarthy L.J., Swords D. & Henshilwood K. (2009) Molecular differentiation of infectious pancreatic necrosis virus isolates from farmed and wild salmonids in Ireland. J Fish Diseases 32, 979– 987. Taylor R.S., Crosbie P.B. & Cook M.T. (2009) Amoebic gill disease reistance is not related to the systemic antibody response of Atlantic salm, Salmo salar L. J Fish Diseases 33, 1– 14. Graham D.A., Fringuelli E., Wilson C., Rowley H.M., Brown A., Rodger H., McLoughlin M.F., McManus C., Casey E., McCarthy L.J. & Rowley N.M. (2009) Prospective longitudinal studies of salmonid alphavirus infections on two Atlantic salmon farms in Ireland; evidence for viral persistence. J Fish Diseases 33, 123– 135. Volume33, Issue7July 2010Pages 623-623 ReferencesRelatedInformation

Identifying footprints of selection in stocked brown trout populations: a spatio-temporal approach

Studies of interactions between farmed and wild salmonid fishes have suggested reduced fitness of farmed strains in the wild, but evidence for selection at the genic level is lacking. We studied three brown trout populations in Denmark which have been significantly admixed with stocked hatchery trout (19-64%), along with two hatchery strains used for stocking. The wild populations were represented by contemporary samples (2000-2006) and two of them by historical samples (1943-1956). We analysed 61 microsatellite loci, nine of which showed putative functional relationships [expressed sequence tag (EST)-linked or quantitative trait loci]. F(ST)-based outlier tests provided support for diversifying selection at chromosome regions marked by three loci, two anonymous and one EST-linked. Patterns of differentiation suggested that the loci were candidates for being under diversifying hitch-hiking selection in hatchery vs. wild environments. Analysis of hatchery strain admixture proportions showed that in one wild population, two of the loci showed significantly lower admixture proportions than the putatively neutral loci, implying contemporary selection against alleles introduced by hatchery strain trout. In the most strongly admixed population, however, there was no evidence for selection, possibly because of immigration by stocked trout overcoming selection against hatchery-derived alleles or supportive breeding practices allowing hatchery strain trout to escape natural selection. To our knowledge, this is the first study demonstrating footprints of selection in wild salmonid populations subject to spawning intrusion by farmed fish.

Patterns of Ichthyobodo necator sensu stricto infections on hatchery-reared Atlantic salmon Salmo salar in Norway

Infection patterns with ectoparasitic flagellates belonging to the genus Ichthyobodo were studied in an Atlantic salmon Salmo salar (L.) hatchery in western Norway during an 11 mo period, from eyed eggs to smoltification. Since the earlier species designation Ichthyobodo necator (sensu lato, s.l.) has been shown to represent a complex of several species, the epizootiology of different Ichthyobodo spp. is poorly known. Therefore, we employed molecular methods to ascertain the specific identity of the parasites detected in our study. Only I. necator in the recently redefined and restricted sense occurred (I. necator sensu stricto, s.s.). We observed a 2-peak pattern of infection; the first peak occurred among fry in March and the second peak among fingerlings and pre-smolt in August and September. Skin lesions observed on fingerlings and pre-smolt were significantly associated with Ichthyobodo infections. Also, these infections were negatively correlated with both haematocrit values (Hct) and the condition factor (K) of the fish. The patterns of infection on the farmed salmon suggest that I. necator s.s. is an opportunistic parasite of salmon, flourishing in periods when susceptible hosts are present and the environment favours parasite proliferation. Our study is the first to detect and identify I. necator s.s. on wild-caught adult salmonids (brown trout S. trutta L.). Wild salmonids and sticklebacks Gasterosteus aculeatus (L.) caught in the lakes serving as a water supply to the hatchery were found infected with I. necator s.s., hence these are the likely sources of parasites entering the hatchery via the inlet water.

Coastal fish farming does not affect the total parasite communities of wild fish in SW Mediterranean

The influence of sea-cage salmon farms in increasing the parasite loads of wild salmonids has received considerable attention due to the potential negative consequences for both natural populations and cultivated stock. However, studies dealing with the parasitological loads of reared fish of other species and their relation with farm-associated wild fish are scarce. In this work, cultured and aggregated, wild fish from 3 different fish farms and 2 control locations were compared by hook and line and spear-fishing. It was found that reared sea bass ( Dicentrarchus labrax) and sea bream ( Sparus aurata) did not share macroparasites with farm-associated wild fish (bogue Boops boops and Mediterranean horse mackerel Trachurus mediterraneus). Similarly, no effect of farms on the total parasite community was detected when it was compared farm-associated and not farm-associated wild bogue and mackerel neither a host-range enlargement that has been detected in some other works. Reduced numbers of cestodes, nematodes and the digenean Lecithocladium excisum (which is first recorded parasitizing T. mediterraneus) occurred in farm-associated wild fish compared to not farm-associated fish. In contrast, the digenean parasites Bacciger israelensis and Prodistomum polonii were favoured by the farm effect. Influence of farms on wild fish, such as diet modification, may be detrimental for some parasite species, while these same conditions could enhance others.

Molecular differentiation of infectious pancreatic necrosis virus isolates from farmed and wild salmonids in Ireland

This study investigated the genotypes and sub-groups of infectious pancreatic necrosis virus (IPNV) present in farmed and wild salmonid fish in Ireland. An 1100-bp portion of the VP2 region of segment A from each of 55 IPNV isolates collected over 2003-2007 was amplified by reverse-transcription-polymerase chain reaction and the product directly sequenced. The nucleotide sequences of each isolate were aligned and compared with each other and with the corresponding sequences of a number of reference isolates. All the 55 sequenced isolates belonged to genogroup 5 (Sp serotype) and could be divided into two subgroups. Irish subgroup 1 consisted of isolates from farmed salmon originating from an Irish salmon broodstock. Irish subgroup 2 consisted of isolates from imported farmed stock and all reported clinical outbreaks of IPN were associated with isolates from subgroup 2. Isolates from wild fish were identical to some isolates from subgroup 2, and therefore are believed to have originated from infected farms. These results highlight the importance of import risk analysis for diseases not listed under current legislation.

Seasonal foraging and piscivory by sympatric wild and hatchery-reared steelhead from an integrated hatchery program

We compared the diet of hatchery-reared steelhead produced from an integrated hatchery program as emigrating spring smolts and non-migrating hatchery residuals to their sympatric wild counterparts. Our results suggest that there is a potential for hatchery fish to affect wild steelhead populations due to dietary overlap and subyearling salmonid predation; however, relative ecological risk did not increase as steelhead delayed or forwent emigration. Predation by hatchery smolts was related to release timing, but not experience with native fish. Diet composition appears to be more strongly affected by seasonal and yearly differences in prey abundance and presence rather than differences in rearing environments. Hatchery and wild steelhead showed small but important foraging differences. Hatchery smolts did not consume as many salmonids as wild fish and hatchery residuals showed relatively stronger surface oriented feeding behavior than wild parr. Because most hatchery smolts emigrated shortly after release and the overall number of residuals in the study creek was low, we speculate that in this case there is low dietary and predatory-based risk of hatchery steelhead in Abernathy Creek negatively impacting wild salmonids.

The first report of Gyrodactylus salaris Malmberg, 1957 (Platyhelminthes, Monogenea) on Italian cultured stocks of rainbow trout ( Oncorhynchus mykiss Walbaum)

The monogenean Gyrodactylus salaris Malmberg, 1957 is considered one of the most important parasites of wild salmonids in the European Community due to the heavy ecological and economical damage it has inflicted on Atlantic salmon ( Salmo salar) parr populations. Rainbow trout ( Oncorhynchus mykiss) is susceptible to G. salaris and can act as a suitable carrier host and, consequently, its trade in EU territory is restricted in relation to the status of “recognized free” zones. Despite the economic importance of rainbow trout farming in Italy, information on the Italian gyrodactylid fauna is lacking and prior to this study, G. salaris had not been officially reported. During a routine health examination of farmed rainbow trout stock throughout Central and Northern Italy in 2004–2005, five fish farms were found to be infected with G. salaris alongside three other gyrodactylids. Morphological and molecular characterisation confirmed the presence of G. salaris, Gyrodactylus teuchis Lautraite, Blanc, Thiery, Daniel et Vigneulle, 1999 and Gyrodactylus derjavinoides Malmberg, Collins, Cunningham et Jalali, 2007, while Gyrodactylus truttae Gläser, 1974 was identified by morphological analysis only. The findings from this study extend the distribution of G. salaris within Europe and highlight the importance of the rainbow trout trade in its dissemination.