Environmental and anthropogenic correlates of hybridization between westslope cutthroat trout (Oncorhynchus clarkii lewisi) and introduced rainbow trout (O. mykiss)

Hybridization with introduced taxa is one of the major threats to the persistence of native biodiversity. The westslope cutthroat trout (Oncorhynchus clarkii lewisi) is found in southeastern British Columbia and southwestern Alberta, Canada, and adjacent areas of Montana, Idaho, and Washington State, USA. Through much of this area, native populations are threatened by hybridization with introduced rainbow trout (O. mykiss). We surveyed 159 samples comprising over 5,000 fish at 10 microsatellite DNA loci to assess the level of admixture between native westslope cutthroat trout (wsct) and introduced rainbow trout in southwestern Alberta. Admixture levels (q_wsct of 0 = pure rainbow trout, q_wsct of 1.0 = pure westslope cutthroat trout) ranged from <0.01 to 0.99 and averaged from 0.72 to 0.99 across seven drainage areas. Regression tree analyses indicated that water temperature, elevation, distance to the nearest stocking site, and distance to the nearest railway line were significant components of a model that explained 34 % of the variation across sites in q_wsct across 58 localities for which habitat variables were available. Partial dependence plots indicated that admixture with rainbow trout increased with increasing water temperature and distance to the nearest railway line, but decreased with increasing elevation and distance from stocking site to sample site. Our results support the hypothesis that westslope cutthroat trout may be less susceptible to hybridization with rainbow trout in colder, higher elevation streams, and illustrate the interaction between abiotic and anthropogenic factors in influencing hybridization between native and introduced taxa.     

Altered gene expression patterns of innate and adaptive immunity pathways in transgenic rainbow trout harboring Cecropin P1 transgene

Background

We have recently developed several homozygous families of transgenic rainbow trout harbouring cecropin P1 transgene. These fish exhibit resistance characteristic to infection by Aeromonas salmonicida and infectious hematopoietic necrosis virus (IHNV). In our earlier studies we have reported that treatment of a rainbow trout macrophage cell line (RTS11) with a linear cationic α-helical antimicrobial peptide (e.g., cecropin B) resulted in elevated levels of expression of two pro-inflammatory relevant genes (e.g., IL-1β and COX-2). Therefore, we hypothesized that in addition to the direct antimicrobial activity of cecropin P1 in the disease resistant transgenic rainbow trout, this antimicrobial peptide may also affect the expression of immune relevant genes in the host. To confirm this hypothesis, we launched a study to determine the global gene expression profiles in three immune competent organs of cecropin P1 transgenic rainbow trout by using a 44k salmonid microarray.

Results

From the microarray data, a total of 2480 genes in the spleen, 3022 in the kidney, and 2102 in the liver were determined as differentially expressed genes (DEGs) in the cecropin P1 transgenic rainbow trout when compared to the non-transgenics. There were 478 DEGs in common among three tissues. Enrichment analyses conducted by two different bioinformatics tools revealed a tissue specific profile of functional pathway perturbation. Many of them were directly related to innate immune system such as phagocytosis, lysosomal processing, complement activation, antigen processing/presentation, and leukocyte migration. Perturbation of other biological functions that might contribute indirectly to host immunity was also observed.

Conclusions

The gene product of cecropin P1 transgene produced in the disease resistant transgenic rainbow trout not only can kill the pathogens directly but also exert multifaceted immunomodulatory properties to boost host immunity. The identified genes involved in different pathways related to immune function are valuable indicators associated with enhanced host immunity. These genes may serve as markers for selective breeding of rainbow trout or other aquaculture important fish species bearing traits of disease resistance.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-887) contains supplementary material, which is available to authorized users.     

Invasive rainbow trout affect habitat use,feeding efficiency,and spatial organization of warpaint shiners

Rainbow trout have been introduced to six of the seven continents and currently are widely stocked for sport fishing. Despite their broad distribution, outside of New Zealand, little is known about the effects of rainbow trout on native species, especially fishes. We conducted experiments in an artificial stream to assess hypotheses that stocked rainbow trout significantly affected: (1) mesohabitat use, (2) foraging success, (3) social behavior, and (4) spatial organization of warpaint shiners (Luxilus coccogenis) a common native minnow found in southern Appalachian streams, with similar patterns of microhabitat use to rainbow trout. We replicated experiments at high and low natural densities (two and five warpaint shiners) and spring/fall (12 °C) and summer (17 °C) temperatures. Treatments included: (1) a control (five warpaint shiners), (2) trout (five warpaint shiners and one rainbow trout), (3) large fish control (five warpaint shiners and one river chub) and (4) density control (six warpaint shiners). The presence of rainbow trout produced a shift by warpaint shiners from pool mesohabitats to shallower, higher velocity habitats with more variable substrata, as well as reduced prey capture success, feeding efficiency, and distance from the front of the tank (i.e., warpaint shiners moved closer to food release points), and increased the distance to the additional fish (i.e., avoidance of the rainbow trout). Negative effects on foraging behaviors were stronger in 12 °C treatments. In a realistic stream flume the presence of rainbow trout produced effects that likely influenced individual fitness of warpaint shiners. The potential effects of stocking rainbow trout on native non-game fishes, such as warpaint shiners should be assessed when implementing or evaluating stocking programs.     

Hilyses®, fermented Saccharomyces cerevisiae, enhances the growth performance and skin non-specific immune parameters in rainbow trout (Oncorhynchus mykiss)

Effects of Hilyses^®, fermented Saccharomyces cerevisiae (S. cerevisiae), on growth, body composition and skin mucus immune components in rainbow trout were quantified. Ninety rainbow trout (105 ± 5 g) were randomly assigned to 2 groups in triplicates and fed dietary Hilyses^® (5 g kg^?1) or control diet without Hilyses^® for 50 days. Results of this study demonstrated that growth performance increased significantly by the dietary yeast supplement; however body composition was not affected in treatment group. At the 45th and 50th day of feeding trial, results of mucus samples demonstrated that yeast supplementation in treatment group significantly promoted enzyme activities, namely lysozyme, protease, alkaline phosphatase and esterase compared to control group. Significant increases were also observed in hemagglutination and antibacterial activity against Yersinia ruckeri in fish fed treatment diet. The present study suggests that fermented S. cerevisiae may effectively promote the growth performance and skin non-specific immune parameters in rainbow trout.     

Selenium Species and Their Distribution in Freshwater Fish from Argentina

The distribution and speciation of selenium (Se) in freshwater fish (muscle and liver tissue) from lakes in Argentina was investigated. Three introduced species, brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis), and one native species, creole perch (Percichthys trucha), were investigated. Values for total selenium in muscle ranged from 0.66 to 1.61 μg/g, while in the liver, concentrations were much higher, from 4.46 to 73.71 μg/g on a dry matter basis. Separation of soluble Se species (SeCys₂, selenomethionine (SeMet), SeMeSeCys, selenite and selenate) was achieved by ion exchange chromatography and detection was performed by inductively coupled plasma–mass spectrometry. The results showed that in fish muscle, from 47 to 55 % of selenium was soluble and the only Se species identified was SeMet, which represented around 80 % of soluble Se, while in the liver, the amount of soluble Se ranged from 61 to 76 % and the percentage of species identified (SeMet and SeCys₂) was much lower and ranged from 8 to 17 % of soluble Se.     

Unidentified cells reside in fish skeletal muscle

Cell cultures were established from the skeletal muscle tissue of 6–13 months old rainbow trout and 12–14 months old yellow perch. Approximately 27,000 ± 5,000 cells/g (trout; N = 5) and 5,000 ± 1,200 cells/g of tissue (perch; N = 4) were obtained. Isolation and propagation were qualitatively greater for both species when the cells (younger fish producer more cells than older fish) were exposed to DMEM + 15% FBS, rather than L-15 + 15% FBS, at 20 °C (trout) and at 24 °C (yellow perch). Two morphologically distinct cell types were observed in cultures of both species, some of which eventually formed very small myotubes, which displayed immunocytological reactivity for myogenin, myosin heavy chain, and α-actinin; the second population of cells remained unstained. Successful cryopreservation was achieved using a 5% DMSO and 95% serum mixture, but post-thawing viabilities were low 5–27% (trout) and 14–30% (perch). Further research is needed in order to determine cell type specificity of isolated cells.     

Observational and experimental studies on the acquisition of Anisakis sp. larvae (nematoda: Ascaridida) by trout in fresh water

In the enclosed fresh-water environmsnt of Hanningfield Reservoir, Essex, England, Anisakis sp. larvae (parasites of marine fish) were found in 55 per cent of 40 brown trout and in 26·2 per cent of 61 rainbow trout. Experimental infection by intubating larvae into the stomach was more successful in brown trout (50·6 per cent recovery rate) than in rainbow trout (27 per cent recovery rate). Some larvae reached the body-cavity as early as 2 h after infection. They penetrated the region between the oesophagus and intestine immediately posterior to the caecal openings. Fewer larvae successfully penetrated the gut wall of brown trout within 24 h at 8°C than at 15 ± 1°C. It appears that the reservoir trout acquired Anisakis by being fed as juveniles on untreated marine fish offal containing live larvae.     

The red alga Porphyra dioica as a fish-feed ingredient for rainbow trout (Oncorhynchus mykiss): effects on growth, feed efficiency, and carcass composition

Porphyra dioica meal was added at levels of 5, 10 and 15% to a diet for rainbow trout formulated to be isonitrogenous and isolipidic. The control diet was a commercial trout diet without seaweed meal. The experimental groups were fed in triplicate for 12.5 weeks, during which fish weight increased on average from 107–261 g. Seaweed meal inclusion did not affect significantly weight gain (WG), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER) and apparent digestibility coefficient of the dry matter (ADC_dm) for any of the diets. Voluntary feed intake (VFI) increased for all seaweed diets compared to the control diet but not significantly (P?>?0.05). Final weight (FW) was significantly smaller for the 15% P. dioica inclusion and hepatosomatic index (HSI) for the 10% and 15% inclusion. Carcass protein content increased for all three experimental diets, and was significantly higher for the diet with 10% seaweed inclusion. Rainbow trout fed with Porphyra meal presented a dark orange pigmentation of the flesh at the end of the trial, compared to the whitish color from the control fish. These results suggest that P. dioica can effectively be included in diets for rainbow trout up to 10% without significant negative effects on weight gain and growth performance. The pigmentation effect of the fish flesh by adding P. dioica meal to the feed is of a considerable interest to the organic salmon-farming industry.     

Expression patterns of gdnf and gfrα1 in rainbow trout testis

In mice, glial cell line-derived neurotrophic factor (GDNF) is essential for normal spermatogenesis and in vitro culture of spermatogonial stem cells. In murine testes, GDNF acts as paracrine factor; Sertoli cells secrete it to a subset of spermatogonial cells expressing its receptor, GDNF family receptor α1 (GFRα1). However, in fish, it is unclear what types of cells express gdnf and gfrα1. In this study, we isolated the rainbow trout orthologues of these genes and analyzed their expression patterns during spermatogenesis. In rainbow trout testes, gdnf and gfrα1 were expressed in almost all type A spermatogonia (ASG). Noticeably, unlike in mice, the expression of gdnf was not observed in Sertoli cells in rainbow trout. During spermatogenesis, the expression levels of these genes changed synchronously; gdnf and gfrα1 showed high expression in ASG and decreased dramatically in subsequent developmental stages. These results suggested that GDNF most likely acts as an autocrine factor in rainbow trout testes.     

Peptidylarginine deiminase gene is differentially expressed in freshwater and brackish water rainbow trout

Peptidylarginine deiminase (PADI)-like cDNA sequence was isolated from rainbow trout (Oncorhynchus mykiss). It consists of a 111-bp 5′-untranslated region, a 731-bp 3′-UTR, and a 2,010-bp open reading frame encoding a protein of 669 amino acids. In the presence of calcium ions, PADI enzymes catalyze the post-translational modification reaction generating citrulline residues. Mammalian PADI enzymes are involved in a number of regulatory processes during cell differentiation and development such as skin keratinization, myelin maturation, and histone deimination. Though five PADI isotypes have been isolated from mammals, in bony fish only one PADI enzyme is present, which contains conserved amino acid residues responsible for catalysis and calcium ion-binding. Sequence identity of piscine PADI protein sequences available at gene databases exceeds 67%. Phylogenetic analyses revealed that not only piscine, but also amphibian and avian PADI-like proteins share most identical amino acid residues with mammalian PADI2. mRNA level of trout PADI-like gene is high in skin, fin, gills, brain, and spleen of rainbow trout. Quantitative Real-Time RT-PCR revealed that PADI gene is differentially expressed in liver, trunk kidney, and spleen of two trout strains, the freshwater-cultured STEELHEAD trout and the brackish water strain BORN.     

Detection of selection signatures in the genome of a farmed population of anadromous rainbow trout (Oncorhynchus mykiss)

Domestication processes and artificial selection are likely to leave signatures that can be detected at a molecular level in farmed rainbow trout (Oncorhynchus mykiss). These signatures of selection are genomic regions that contain functional genetic variants conferring a higher fitness to their bearers. We genotyped 749 rainbow trout from a commercial population using a rainbow trout Axiom 57 K SNP array panel and identified putative genomic regions under selection using the pcadapt, Composite Likelihood Ratio (CLR) and Integrated Haplotype Score (iHS) methods. After applying quality-control pipelines and statistical analyses, we detected 12, 96 and 16 SNPs putatively under selection, associated with 96, 781 and 115 candidate genes, respectively. Several of these candidate genes were associated with growth, early development, reproduction, behavior and immune system traits. In addition, some of the SNPs were found in interesting regions located in autosomal inversions on Omy05 and Omy20. These findings could represent a genome-wide map of selection signatures in farmed rainbow trout and could be important in explaining domestication and selection for genetic traits of commercial interest.     

Polymorphisms in MHC class Ia genes and resistance to IHNV in rainbow trout (Oncorhynchus mykiss)

Infectious haematopoietic necrosis virus (IHNV) is detrimental to the farming of rainbow trout (Oncorhynchus mykiss) and other salmonids in the Northern hemisphere. The major histocompatibility complex (MHC) plays a key role in immune response in invertebrates, as evidenced by the close correlation of MHC polymorphisms with disease resistance/susceptibility. To analyse the correlation between rainbow trout resistance and susceptibility to IHNV and genetic variation in exon 2 of MHC class Ia gene, UBA, we employed two approaches, namely, polymerase chain reaction-single strand conformation polymorphism analysis and cloning/sequencing. From 102 resistant and 82 susceptible individuals, a total of 12 alleles in UBA exon 2 (GenBank: JX136662–JX136673) were identified, including 11 novel alleles. The maximum number of these alleles in a single individual was four, suggesting that UBA exon 2 most likely resides on at least two loci in the genome. Most of the variations in UBA exon 2 were located in the peptide-binding region and were determined to have been subject to positive selection during evolution. Correlation analysis revealed that Onmy-UBA*0111 and Onmy-UBA*0107 are highly associated with IHNV susceptibility (P = 0.001), whereas Onmy-UBA*0101, Onmy-UBA*0102, and Onmy-UBA*0103 are highly related to IHNV resistance (P = 0.000). In addition, the three resistant alleles were predominant in the IHNV disease-resistant population; thus, these molecular markers can be used for anti-IHNV breeding of rainbow trout.     

Current status and future perspectives of Italian finfish aquaculture

Currently available data show that shellfish and finfish production in Italy, derived both from fisheries and aquaculture activities, is on the order of 474,000 tons, each activity representing 50 % of the total amount. In this context, the finfish aquaculture industry contributes on average 31 % to the national aquaculture production and on average 59 % of its value, giving a total amount of 72,000 tons and a value of around 351 million € (2010). According to FEAP statistics, Italy is the fourth largest finfish producer in EU27, after the UK, Greece, and Spain, while it is also one of the six largest finfish producers among the non-EU and EU member countries, together with Norway, UK, Greece, Turkey, and Spain. Presently, fish culture activities are mainly focused on rainbow trout (Oncorhynchus mykiss, 55.5 %), followed by European sea bass (Dicentrarchus labrax, 13.6 %), gilthead sea bream (Sparus aurata, 12.2 %), gray mullet (Mugil cephalus, 5.3 %), sturgeon (Acipenser spp., 2 %), and European eel (Anguilla anguilla, 1.7 %). Over the last 20 years, freshwater fish production and aquaculture (trout, carp, and eel) have decreased in Italy, with the exception of sturgeon. In contrast, marine fish production has significantly increased during the same period, and the two leading species, European sea bass and gilthead sea bream, presently contribute 25.8 % of the finfish production. From 1,900 tons in 1990, production reached 19,000 tons in 2010, with a 900 % increase, at an average percentage of 4.5 %. In addition, new marine fish species were successfully cultured over the same period. This review outlines the past and present situation of finfish culture in Italy and discusses future developments and priorities, with particular emphasis on new, emerging aquaculture species.     

Immune rainbow trout serum has an anti-proliferation effect on isolated mouse T-cells: Possible autoimmune downregulatory implications

Multiple sclerosis is generally believed to involve an autoimmune syndrome in which affected individuals experience degradation of the myelin sheath in the central nervous system. In this study, rainbow trout were immunized with myelin basic protein and myelin in an attempt to induce a myelin-specific autoimmune response using the experimentally induced autoimmune response in Lewis rats as a model. Subsequent to immunization, rainbow trout antibodies to myelin basic protein were detected via an ELISA. Although clinical signs of nerve dysfunction were never apparent, disease due to demyelinization cannot be ruled out until histological studies are performed. It is shown that both rainbow trout immune and normal sera exert an inhibitory affect on the mitogenic stimulation of isolated mouse splenic T-cells. This in vitro inhibitory activity, which is clearly greater in immune serum, is hypothesized to be derived from a nonspecific antiinflammatory factor. While the identity of the factor(s) is not yet known, likely possibilities are discussed.     

Determining Vaccination Frequency in Farmed Rainbow Trout Using Vibrio anguillarum O1 Specific Serum Antibody Measurements

Background

Despite vaccination with a commercial vaccine with a documented protective effect against Vibrio anguillarum O1 disease outbreaks caused by this bacterium have been registered among rainbow trout at Danish fish farms. The present study examined specific serum antibody levels as a valid marker for assessing vaccination status in a fish population. For this purpose a highly sensitive enzyme-linked immunosorbent assay (ELISA) was developed and used to evaluate sera from farmed rainbow trout vaccinated against V. anguillarum O1.

Study Design

Immune sera from rainbow trout immunised with an experimental vaccine based on inactivated V. anguillarum O1 bacterin in Freund’s incomplete adjuvant were used for ELISA optimisation. Subsequently, sera from farmed rainbow trout vaccinated with a commercial vaccine against V. anguillarum were analysed with the ELISA. The measured serum antibody levels were compared with the vaccine status of the fish (vaccinated/unvaccinated) as evaluated through visual examination.

Results

Repeated immunisation with the experimental vaccine lead to increasing levels of specific serum antibodies in the vaccinated rainbow trout. The farmed rainbow trout responded with high antibody levels to a single injection with the commercial vaccine. However, the diversity in responses was more pronounced in the farmed fish. Primary visual examinations for vaccine status in rainbow trout from the commercial farm revealed a large pool of unvaccinated specimens (vaccination failure rate = 20%) among the otherwise vaccinated fish. Through serum analyses using the ELISA in a blinded set-up it was possible to separate samples collected from the farmed rainbow trout into vaccinated and unvaccinated fish.

Conclusions

Much attention has been devoted to development of new and more effective vaccines. Here we present a case from a Danish rainbow trout farm indicating that attention should also be directed to the vaccination procedure in order to secure high vaccination frequencies necessary for optimal protection with a reported effective vaccine.