Soybean meal-induced enteritis in Atlantic salmon (Salmo salar) and Chinook salmon (Oncorhynchus tshawytscha) but not in pink salmon (O. gorbuscha)

In Atlantic salmon, as in most salmonids, males can mature early in the life cycle, as small freshwater fish, termed parr, and/or undergo a sea migration before maturing as full-size adults. The alternative life histories are contingent on environmental and social circumstances, such as growth rate, territory quality or any other factor that affects the individual's state. In order to model the choice of life history in this group of commercially valuable species, it is necessary to understand not only the relative contribution of the different male types to subsequent generations, but also to know the factors that affect reproductive success in each type. In this paper we present the results of a study designed to investigate the factors that affect the reproductive success of mature parr. We used highly polymorphic minisatellite DNA markers to analyse paternity in a series of mating experiments where the number and body size of parr were manipulated. The fraction of eggs fertilized by mature parr ranged from 26 to 40 per cent, with individual parr fertilizing up to 26 per cent of the eggs. A strong positive correlation was found between parr size and reproductive success. The relative success of parr decreased with increasing parr number. Data from this and other studies on variation in the timing and degree of parr reproductive success are discussed in relation to the evolution of male mating strategies and life history in salmonids.

This study compared the flesh quality of farmed and wild sources of British Columbia (BC) salmon with respect to concentrations of polychlorinated biphenyl compounds, polychlorinated dibenzodioxins/dibenzofurans and their associated toxic equivalents, total mercury (THg), methylmercury (MeHg), and selected fatty acids of known importance for human health viz., omega-3 (n-3) highly unsaturated fatty acids (n-3 HUFAs) and (n-6) fatty acids. Skinned fillets from known sources of farmed Atlantic, coho, and chinook salmon (n = 110) and wild coho, chinook, chum, sockeye, and pink salmon (n = 91) were examined. Atlantic salmon contained higher PCB concentrations (means, 28-38 ng/g) than farmed coho or chinook salmon, and levels in these latter species were similar to those in wild counterparts (means, 2.8-13.7 ng/g). PCB levels in Atlantic salmon flesh were, nevertheless, 53-71-fold less than the level of concern for human consumption of fish, i.e., 2000 ng/g as established by Health Canada and the U.S. Food and Drug Administration (US-FDA). Similarly, THg and MeHg levels in all samples were well below the Health Canada guideline (0.5 microg/g) and the US-FDA action level (1.0 microg/g). On average, THg in farmed salmon (0.021 microg/g) was similar to or lower than wild salmon (0.013-0.077 microg/g). Atlantic salmon were a richer source (mean, 2.34 g/100 g fillet) of n-3 HUFAs than the other farmed and wild sources of salmon examined (means, 0.39-1.17 g/100 g). The present findings support the recommended weekly consumption guidelines for oily fish species (includes all BC salmon sources) for cardio-protective benefits as made by the American Heart Association and the UK Food Standards Agency.

A comparative examination of cortisol effects on muscle myostatin and HSP90 gene expression in salmonids

With different ecological characteristics amongst salmonid species, their response to parasitic infestation is likely to vary according to their spatial and temporal overlap with the parasite. This study investigated the host–parasite interactions amongst three species of salmonids and the ectoparasitic salmon louse, Lepeophtheirus salmonis. To determine any variation in infestation parameters amongst salmonids, single population groups of Atlantic salmon (Salmo salar), chinook salmon (Onchorhynchus tshawytscha), and previously-infested and naïve sea trout (Salmo trutta) were exposed to a controlled infestation challenge. We found that chinook salmon and both sea trout groups were more susceptible to acquiring lice than Atlantic salmon. Behavioural responses during infestation were more pronounced in Atlantic and chinook salmon. Parasite development was similar in lice attached to Atlantic salmon and sea trout, but hindered on chinook salmon. At 16 days post-infestation, chinook salmon had reduced lice loads to the same level as Atlantic salmon, whilst sea trout retained their lice. These results demonstrate differences in interactions with L. salmonis amongst these species, and highlight the vulnerability of sea trout to infestation.

Canadian salmonid aquaculture provides a sustainable protein source; however, there are concerns that Atlantic salmon (Salmo salar L.) mariculture reduces wild Pacific salmon survival through interspecific disease transfer. Tenacibaculosis, caused by species of Gram‐negative bacteria in the genus Tenacibaculum, has the potential to be transmitted interchangeably between farmed Atlantic salmon and wild Pacific salmon, though there is a lack of corroboration establishing transmission. To provide evidence for interspecific horizontal transmission of tenacibaculosis from Atlantic salmon to Pacific salmon, Atlantic salmon were bath‐exposed to an isolate of Tenacibaculum maritimum and cohabitated with naïve Atlantic or Chinook salmon (Oncorhynchus tshawytscha W.) for 25 days. Exposed and naïve cohabitant Atlantic salmon exhibited morbidity with multifocal superficial and ulcerative epidermal lesions with intralesional T. maritimum (culture, histology, and qPCR). At 108 CFU mL−1, exposed and naïve cohabitant Atlantic salmon had 43% and 60% mortality, respectively. Contrastingly, cohabitant Chinook salmon experienced no morbidity or mortality, despite successful culture of T. maritimum (108 CFU mL−1n = 5/6 fish; 106 CFU mL−1n = 0/6 fish) from skin swabs. These findings suggest that BC Chinook salmon do not develop clinical tenacibaculosis through interspecific horizontal transmission from farmed Atlantic salmon with mouthrot under the tested conditions and that the presence of T. maritimum alone is insufficient for disease. Further research needs to clarify the genetic differences between hosts and pathogens in different geographical locations, and investigate additional T. maritimum isolates, alternative Tenacibaculum species, environmental variables, and temporal scales that could lead to clinical tenacibaculosis in Chinook salmon.

BackgroundInfection with the myxozoan parasite Parvicapsula pseudobranchicola causes disease in wild and farmed salmonids in Norway. In the northeast Pacific Ocean, the parasite has been reported in Pacific salmon Oncorhynchus spp. without evidence of disease. The objectives of the present study were to confirm the identity of P. pseudobranchicola in the Pacific, document its host and geographic ranges, and describe associated pathological changes.MethodsOcean-entry year wild pink salmon Oncorhynchus gorbuscha, chum salmon O. keta, Chinook salmon O. tshawytscha, coho salmon O. kisutch and sockeye salmon O. nerka were collected in summer and autumn surveys near Vancouver Island (VI) and from a winter survey in the Gulf of Alaska. Samples were also obtained from farmed Atlantic salmon Salmo salar and Chinook salmon near VI. Samples were analysed by qPCR and histology using conventional staining or in situ hybridisation. Parasite sequence was obtained from small subunit ribosomal RNA gene (SSU rDNA).ResultsIdentical 1525 base-pair SSU rDNA sequences from infected pink salmon, chum salmon and Chinook salmon shared 99.93% identity with a P. pseudobranchicola sequence from Norwegian Atlantic salmon. In autumn surveys, the prevalence was greatest in chum salmon (91.8%) and pink salmon (85.9%) and less so in Chinook salmon (68.8%) and sockeye salmon (8.3%). In farmed salmon, the prevalence was zero in Atlantic salmon (n = 967) and 41% in Chinook salmon (n = 118). Infections were preferentially sited in pseudobranch and visualised by in situ hybridisation. Heavy parasite burdens in all species of Pacific salmon were inconsistently associated with focal granulomatous pseudobranchitis.ConclusionsIn the northeast Pacific, widespread occurrence of P. pseudobranchicola in Pacific salmon together with its absence or sporadic occurrence in farmed Atlantic salmon differs from its epidemiology in Norway, despite similar pathological development in the pseudobranch. Consequences of the infections to the health of wild Pacific salmon, identity of the invertebrate host and the distribution and abundance of infective actinospores are unknown and remain high priorities for research.Graphical

A tool to identify pink salmon ( Oncorhynchus gorbuscha) × Chinook salmon ( O. tshawytscha) hybrids in the St. Marys River, Michigan–Ontario

BackgroundSalmon species vary in susceptibility to infections with the salmon louse (Lepeophtheirus salmonis). Comparing mechanisms underlying responses in susceptible and resistant species is important for estimating impacts of infections on wild salmon, selective breeding of farmed salmon, and expanding our knowledge of fish immune responses to ectoparasites. Herein we report three L. salmonis experimental infection trials of co-habited Atlantic Salmo salar, chum Oncorhynchus keta and pink salmon O. gorbuscha, profiling hematocrit, blood cortisol concentrations, and transcriptomic responses of the anterior kidney and skin to the infection.ResultsIn all trials, infection densities (lice per host weight (g)) were consistently highest on chum salmon, followed by Atlantic salmon, and lowest in pink salmon. At 43 days post-exposure, all lice had developed to motile stages, and infection density was uniformly low among species. Hematocrit was reduced in infected Atlantic and chum salmon, and cortisol was elevated in infected chum salmon. Systemic transcriptomic responses were profiled in all species and large differences in response functions were identified between Atlantic and Pacific (chum and pink) salmon. Pink and chum salmon up-regulated acute phase response genes, including complement and coagulation components, and down-regulated antiviral immune genes. The pink salmon response involved the largest and most diverse iron sequestration and homeostasis mechanisms. Pattern recognition receptors were up-regulated in all species but the active components were often species-specific. C-type lectin domain family 4 member M and acidic mammalian chitinase were specifically up-regulated in the resistant pink salmon.ConclusionsExperimental exposures consistently indicated increased susceptibility in chum and Atlantic salmon, and resistance in pink salmon, with differences in infection density occurring within the first three days of infection. Transcriptomic analysis suggested candidate resistance functions including local inflammation with cytokines, specific innate pattern recognition receptors, and iron homeostasis. Suppressed antiviral immunity in both susceptible and resistant species indicates the importance of future work investigating co-infections of viral pathogens and lice.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-200) contains supplementary material, which is available to authorized users.

Piscirickettsia salmonis, the aetiological agent of salmonid rickettsial septicaemia (SRS), is a global pathogen of wild and cultured marine salmonids. Here, we describe the development and application of a reproducible, standardized immersion challenge model to induce clinical SRS in juvenile pink (Oncorhynchus gorbuscha), Atlantic (Salmo salar) and sockeye salmon (O. nerka). Following a 1‐hr immersion in 105 colony‐forming units/ml, cumulative mortality in Atlantic salmon was 63.2% while mortality in sockeye salmon was 10%. Prevalence and levels of the bacterium in kidney prior to onset of mortality were lower in sockeye compared with Atlantic or pink salmon. The timing and magnitude of bacterial shedding were estimated from water samples collected during the exposure trials. Shedding was estimated to be 82‐fold higher in Atlantic salmon as compared to sockeye salmon and peaked in the Atlantic salmon trial at 36 d post‐immersion. These data suggest sockeye salmon are less susceptible to P. salmonis than Atlantic or pink salmon. Finally, skin lesions were observed on infected fish during all trials, often in the absence of detectable infection in kidney. As a result, we hypothesize that skin is the primary point of entry for P. salmonis during the immersion challenge.

For Pacific salmonids, a key fisheries forensics and management goal is to identify individuals to specific species and potentially specific populations or geographic regions within species. Genetic variation can be used for both species and individual identification, and variation at single nucleotide polymorphisms (SNPs) within two specific DNA amplicons was used to distinguish among coho salmon (Oncorhynchus kisutch), Chinook salmon (Oncorhynchus tshawytscha), sockeye salmon (Oncorhynchus nerka), chum salmon (Oncorhynchus keta), pink salmon (Oncorhynchus gorbuscha), masu salmon (Oncorhynchus masou), steelhead/rainbow trout (Oncorhynchus mykiss), cutthroat trout (Oncorhynchus clarkii), and Atlantic salmon (Salmo salar). A total of 2510 individuals was evaluated from a Pacific rim distribution of populations for sockeye salmon, chum salmon, and pink salmon, whereas masu salmon samples were genotyped only from Japanese populations. Coho salmon, Chinook salmon, steehead trout, cutthroat trout, and Atlantic salmon samples were genotyped only from North American populations. All individual salmonids genotyped were assigned with 100% accuracy to their respective species via diagnostic homozygous SNP genotypes for each species except for cutthroat trout, where no diagnostic SNP genotypes were observed in the two amplicons evaluated.

– Atlantic salmon (Salmo salar) was once native to Lake Ontario, however, its numbers rapidly declined following colonisation by Europeans and the species was extirpated by 1896. Government agencies surrounding Lake Ontario are currently undertaking a variety of studies to assess the feasibility of reintroducing Atlantic salmon. We released hatchery‐reared adult Atlantic salmon into a Lake Ontario tributary to examine spawning interactions between this species and fall‐spawning exotic salmonids found in the same stream. Chinook salmon, coho salmon and brown trout were observed interacting with spawning Atlantic salmon in nearly one‐quarter of our observation bouts, with chinook salmon interacting most frequently. Whereas a previous investigation found that chinook salmon caused elevated agonistic behaviour and general activity by spawning Atlantic salmon, the present study found that interspecific courtship was the most common form of exotic interaction with spawning Atlantic salmon. In particular, we observed precocial male Chinook salmon courting female Atlantic salmon and defending the female against approach by male Atlantic salmon. We discuss the potential implications of these interactions on the Lake Ontario Atlantic salmon reintroduction programme.

Oxytetracycline (OTC) tissue distribution and elimination by sea water salmon were studied using seapen-cultured chi-nook salmon, Oncorhynchus tshawytscha, and Atlantic salmon, Salmo salar. Chinook salmon were treated with OTC-medicated feed at a rate of 100 mg OTC/kg body weight per day for 10 days in 9°C or 12°C sea water. Atlantic salmon were treated by the same medicated feed and dosage in 7,2°C sea water. At specific time points, 3 or 6 salmon were removed from each sea-pen, sacrificed, and analysed for OTC with HPLC. OTC concentration profiles in chinook salmon tissues were found to be very similar to those of the Atlantic salmon. Tissue OTC concentrations in the salmonids generally decreased in the order of liver>kidney>skin>muscle at the end of the treatment period. The elimination of OTC from the muscle of chinook salmon was markedly affected by water temperature; the half-lives t\\a of OTC elimination from the muscle were 13.59 days and 10.34 days at 9°C and 12°C, respectively. The t\\a of OTC elimination from the muscle of Atlantic salmon was 15.75 days at 7.2°C. These results show that the pharmacokinetics of OTC in Atlantic and chinook salmon are very similar afterperos administration. As a result, OTC pharmacokinetics obtained from a chinook salmon study can be used for dosage adjustment and withdrawal time determination in Atlantic salmon and vice versa

We analyzed the abundance and spatial distribution of spawning pink salmon Oncorhynchus gorbuscha, chum salmon O. keta, and Chinook salmon O. tshawytscha in a 27-mi section of the upper Skagit River, Washington, regulated by the Skagit Hydroelectric Project. Densities of spawning salmon were compared among three contiguous reaches of the upper Skagit River before and after the implementation of flow management measures in 1981. The measures were intended to minimize redd dewatering during the spawning and incubation periods and fry stranding during the emergence and outmigration periods. Field monitoring confirmed that increasing the minimum incubation flows created improvements in redd protection levels. Greater protection of fry from stranding was achieved by substantially reducing the annual number of downramping events and by reducing downramping during daytime, when fry are most vulnerable to stranding. Spawner abundance of all three species progressively increased in an upstream direction following implementation of flow measures; increases were greatest in the reach immediately below the hydroelectric project. The upstream shift in spawner abundance was highly significant based on factorial analyses of variance. The greatest increases in spawner abundance for Chinook salmon and chum salmon were observed during even years, when pink salmon did not spawn. Mean spawner abundance in the upstream-most study reach increased from 311 to 1,169 carcasses/mi (odd years) for pink salmon, from 6 to 115 fish/mi (odd years) or 58 to 462 fish/mi (even years) for chum salmon, and from 48 to 49 redds/mi (odd years) or 59 to 65 redds/ mi (even years) for Chinook salmon. The total number of pink salmon and chum salmon spawners significantly increased within the study area after 1981. These increases were substantially greater than those observed concurrently in other areas of the Skagit River basin and in other northern Puget Sound rivers. The average number of Chinook salmon spawners remained unchanged in the study area after 1981, while substantially declining in other unregulated Skagit River subbasins and most Puget Sound rivers. The study area now possesses the greatest percentage of pink, chum, and Chinook salmon spawners within the Skagit River basin. The Skagit River presently supports the largest run of native Chinook salmon in the Puget Sound region and the largest runs of pink and chum salmon in the coterminous United States.

The present study reports measured levels of organochlorine pesticides (OCPs) in commercial salmon feed (n = 8) and farmed Atlantic, coho, and chinook salmon (n = 110), as well as wild coho, chinook, chum, sockeye, and pink salmon (n = 91). Flesh residue concentrations (ng/g wet weight) of dichlorodiphenyltrichloroethanes (DDTs), hexachlorocyclohexanes (HCHs), chlordanes, chlorobenzenes (CBz) and cyclodiene pesticides (e.g., dieldrin, mirex) were 2 to 11 times higher (p < 0.05) in farmed salmon compared with wild salmon. Concentrations were positively correlated with flesh lipid levels. Farmed Atlantic salmon (12-15% lipid) typically exhibited the greatest OCP burdens compared with other salmon species. However, when expressed on a lipid weight basis, concentrations of OCPs (ng/g lipid weight) in wild salmon, in many cases, exceeded those levels in farmed salmon. Observed interspecies and site-specific variations of OCP concentrations in farmed and wild salmon may be attributed to divergent life history, prey/feed characteristics and composition, bioenergetics, or ambient environmental concentrations. Calculated biomagnification factors (BMF = C(F)/C(D), lipid wt) of OCPs in farmed salmon typically ranged between two and five. Biomagnification of chemicals such as DDTs, chlordanes, and mirex was anticipated, because those compounds tend to exhibit high dietary uptake and slow depuration rates in fish because of relatively high octanol-water partition coefficients (K(OW)s > 10⁵). Surprisingly, less hydrophobic pesticides such as hexachlorocyclohexanes and endosulfans (K(OW) s < 10⁵) consistently exhibited a high degree of biomagnification in farmed salmon species (BMFs > 5). This is contrary to previous laboratory and field observations demonstrating fish BMFs less than 1 for low K(OW) chemicals, because of efficient respiratory elimination of those compounds via gills. The results suggest that ambient seawater concentrations and bioconcentration-driven accumulation may play a key role in the bioaccumulation of these relatively more water-soluble contaminants in farmed salmon. Finally, OCP exposure through consumption of British Columbian salmon is found to be low relative to United States national average per capita total exposure levels and provisional tolerable daily intakes.

Early marine life history of juvenile Pacific salmon in two regions of Puget Sound