Strains Of Rainbow Trout Research Articles

Comparative susceptibility of Atlantic salmon and rainbow trout to Yersinia ruckeri: Relationship to O antigen serotype and resistance to serum killing

A study was undertaken to compare the virulence and serum killing resistance properties of Atlantic salmon and rainbow trout Yersinia ruckeri isolates. Five isolates, covering heat-stable O-antigen O1, O2 and O5 serotypes, were tested for virulence towards fry and juveniles of both species by experimental bath challenge. The sensitivity of 15 diverse isolates to non-immune salmon and rainbow trout serum was also examined. All five isolates caused significant mortality in salmon fry. Serotype O1 isolate 06059 caused the highest mortality in salmon (74% and 70% in fry and juveniles, respectively). Isolate 06041, a typical ERM-causing serotype O1 UK rainbow trout strain, caused mortalities in both rainbow trout and salmon. None of the salmon isolates caused any mortalities in 150–250g rainbow trout, and only serotype O2 isolate 06060 caused any significant mortality (10%) in rainbow trout fry. Disease progression and severity was affected by water temperature. Mortality in salmon caused by the isolates 06059 and 05094 was much higher at 16°C (74% and 33%, respectively) than at 12°C (30 and 4% respectively). Virulent rainbow trout isolates were generally resistant to sera from both species, whereas salmon isolates varied in their serum sensitivity. Convalescent serum from salmon and rainbow trout that had been infected by serotype O1 isolates mediated effective classical pathway complement killing of serotype O1 and O5 isolates that were resistant to normal sera. Overall, strains recovered from infected salmon possess a wider range of phenotypic properties (relative virulence, O serotype and possession of serum-resistance factors), compared to ERM-causing rainbow trout isolates.

Molecular characterization of PRR13 and its tissue-specific expression in rainbow trout (Oncorhynchus mykiss)

The proline-rich protein 13 (PRR13) is reported to be a key regulator of the resistance to cytostatica by decreasing the copy number of the proapoptotic gene thrombospondin-1. We isolated and characterized the complete PRR13 gene sequence of rainbow trout (Oncorhynchus mykiss). The gene comprises four exons and three introns, the latter of comparatively short lengths (100-811bp). The full-length PRR13 cDNA consists of 1,101 nucleotides, including an open reading frame of 563bp, which is predicted to encode a 187 amino acid protein with a molecular mass of 18.8kDa. A continuous stretch of ten serine residues at the C-terminus is highly conserved and characteristic for vertebrate PRR13, but not for other known proline-rich proteins. Phylogenetic analyses suggest a clear separation of teleostean PRR13 proteins and those from mammalian and reptilian species. Comparison of the tissue-specific PRR13 mRNA abundance in two strains of the rainbow trout coastal form (TCO Steelhead II-WA vs. BORN Steelhead II-Germany) revealed an increased expression in the BORN trout in nearly all examined tissues. The major expression differences were detected in gill (2.29-fold) and in liver tissue (2.16-fold). Hence, the increased PRR13 expression in BORN trout might cause improved protection from natural cytostatica and therefore support our assumption that PRR13 is a candidate gene possibly involved in the varying ability of the two rainbow trout strains to handle environmental stress under local conditions of the Southern Baltic.

Invasion of Ceratomyxa shasta (Myxozoa) and comparison of migration to the intestine between susceptible and resistant fish hosts

The myxozoan parasite Ceratomyxa shasta infects salmonids causing ceratomyxosis, a disease elicited by proliferation of the parasite in the intestine. This parasite is endemic to the Pacific Northwest of North America and salmon and trout strains from endemic river basins show increased resistance to the parasite. It has been suggested that these resistant fish (i) exclude the parasite at the site of invasion and/or (ii) prevent establishment in the intestine. Using parasites pre-labeled with a fluorescent stain, carboxyfluorescein succinimidyl diacetate (CFSE), the gills were identified as the site of attachment of C. shasta in a susceptible fish strain. In situ hybridization (ISH) of histological sections was then used to describe the invasion of the parasites in the gill filaments. To investigate differences in the progress of infection between resistant and susceptible fish, a C. shasta-susceptible strain of rainbow trout ( Oncorhynchus mykiss) and a C. shasta-resistant strain of Chinook salmon ( Oncorhynchus tshawytscha) were sampled at consecutive time points following exposure at an endemic site. Using ISH in both species, the parasite was observed to migrate from the gill epithelium into the gill blood vessels where replication and release of parasite stages occurred. Quantitative PCR verified entry of the parasite into the blood. Parasite levels in blood increased 4 days p.i. and remained at a consistent level until the second week when parasite abundance increased further and coincided with host mortality. The timing of parasite replication and migration to the intestine were similar for both fish species. The field exposure dose was unexpectedly high and apparently overwhelmed the Chinook salmon’s defenses, as no evidence of resistance to parasite penetration into the gills or prevention of parasite establishment in the intestine was observed.

Use of meristic counts and skeletal anomalies to assess developmental plasticity of farmed rainbow trout (Oncorhynchus mykiss, Walbaum 1792): a preliminary study

Summary Rainbow trout is the longest-standing intensively-reared species in Western countries, where it has been subjected by farmers to selection for productive traits for more than a century. One interesting aspect in this context is to try and understand if prolonged artificial selection has in some way altered the phenotypic plasticity of this species. In this preliminary study, we characterized meristic counts and skeletal abnormalities in two different (Italian and French) rainbow trout strains, reared during on-growing following different approaches (intensive and semi-intensive), in order to analyze whether there are any differences in the skeletal elements and if so, what. Despite the different genetic origin and rearing methodologies to which the lots analyzed were subjected, the occurrences of malformed and seriously malformed individuals were not significantly different, nor were the mean number of anomalies per specimen. The body region most affected by deformities was the caudal vertebral column in both lots, although the French lot was also characterized by an high occurrence of spinal anomalies in the haemal region. Among the meristic counts, only the number of anal and dorsal rays showed statistically different median values between the two lots.

Side effects of sexual maturation on heritability estimates in rainbow trout (Oncorhynchus mykiss)

In ¢sh, sexual maturation is often considered to be a problem because it perturbs growth and product quality. Therefore, it is common to select against early-maturing males in commercial breeding programmes (Gjedrem 2000). Genetic determinism of age at sexual maturation has been extensively studied in many species, and even some QTLs have been found (e.g. Gjerde 1986; Hankin, Nicholas & Downey 1993; Longalong, Eknath & Bentsen 1999; Kause, Ritola, Paananen, Mantysaari & Eskelinen 2003; Haidle, Janssen, Gharbi, Moghadam, Ferguson & Danzmann 2008). However, the eiect of sexual maturation on heritability estimates for other traits is not documented. In this paper, we present data collected during the beginningof sexualmaturationof a group of rainbow trout and showhow it biases heritability estimations. The ¢sh studied were issued froma full-factorial mating between two dams and 45 sires. Fish were all reared in the same tank since the eyed stage under a natural photoperiod and pedigrees were redrawn using10 microsatellites. Fishwere harvested in April at 17 months of age. They were killed on ice and several growth and quality traits were determined. Body weight was the main trait studied in this paper. The sex of the ¢sh was recorded by visual inspection of the gonads. For females, none of the individuals showed signs of maturation. For males, observers attempted to diierentiate non-maturing and maturing males but it turned out to be di⁄cult because we were at the very beginning of the maturation (this rainbow trout strain usually spawns in November^ December). However, we recorded gonads weight to enable calculation of the gonado-somatic index (GSI5100 gonads weight/body weight), which was used to determine which males were maturing or not.We studied several GSI thresholds: 0.1, 0.2, 0.3, 0.4 and 0.5. For each threshold, males with GSI above the threshold were considered to be maturing males. We studied sex eiect and heritability estimates for each threshold. Heritability was estimated using VCE5 (Groeneveld & Kovac 1990) with a sire model and sex and dam as ¢xed eiects. Dam was set as a ¢xed eiect because there were only two dams in our mating design, and therefore between-dams variance is of no interest. Two dams were used instead of one in order to avoid confusion of dominance eiects with additive genetic eiects in the between-sires variance. Moreover, this design was demonstrated to be e⁄cient for estimating heritabilities when the total number of oispring analysed is ¢xed (Dupont-Nivet, Vandeputte & Chevassus 2002). First, we analysed all the datasets with a sex eiect comprising three levels (female, male and maturing male). Second, maturing males were removed from the dataset and the sex effect was set to two levels (male and female). Using ‘FAP’ software (Taggart 2007), 87% of ¢sh could be attributed to their parents. Oispring from two sires with less than three oispring were removed from the data set. Four hundred and thirty-three animals were ¢nally analysed. The sex ratio was well equilibrated with 217 females, i.e., 50.1%. In Table 1, Aquaculture Research, 2010, 41, e878^e880 doi:10.1111/j.1365-2109.2009.02448.x

Expression of immune-regulatory genes, arginase-2 and inducible nitric oxide synthase (iNOS), in two rainbow trout (Oncorhynchus mykiss) strains following exposure to Myxobolus cerebralis

The present endeavor was conducted to evaluate the role of activated macrophage in the susceptibility of two different rainbow trout (Oncorhynchus mykiss) strains, a susceptible American (T) and a more resistant German (H), to infection with Myxobolus cerebralis. Arginase-2 and inducible nitric oxide synthase (iNOS) genes were used as references to the alternative and classical pathway of macrophage activation. The expression level of both genes was measured using quantitative real-time polymerase chain reaction. The expression level of arginase-2 was significantly upregulated in strain T at 2 h and 8 days post exposure in the strain H. In case of iNOS, the expression level was significantly upregulated from 24 h to 8 days p.e. in strain T and only in 8 days p.e. in strain H. During this study also, the influence of nitric oxide (NO) on the viability of the triactinomyxon spores (TAMs) of M. cerebralis was evaluated using the NO-donor S-nitroso-N-acetyl-penicillamine (SNAP). Rising final concentrations of SNAP from 0.25 to 1 mM at 2, 4, and 24 h resulted in increasing numbers of propidium iodide-positive TAMs detected. The results of this study suggest an inability of strain T to react with an effective immune response against infection with M. cerebralis. Furthermore, the TAMs of M. cerebralis react with significant decrease of viable spores to rising concentration of SNAP and longer incubation, but there is also evidence for some resistance to NO activity.

Effects of Ceratomyxa shasta dose on a susceptible strain of rainbow trout and comparatively resistant Chinook and coho salmon

Ceratomyxa shasta infects salmon and trout, causing ceratomyxosis, a disease characterized by parasite proliferation in the intestine and death. We used laboratory challenges to investigate the infective dose for 3 fish species: a susceptible strain of rainbow trout Oncorhynchus mykiss and comparatively resistant Chinook O. tshawytscha and coho salmon O. kisutch. For susceptible rainbow trout, we determined the outcome of infection under conditions of varying parasite dose, fish size, and parasite concentration. A single actinospore was sufficient to cause a lethal infection in susceptible rainbow trout. The mean days to death (MDD) did not significantly decrease among doses causing 100% prevalence, indicating a minimum time required for parasites to replicate to a fatal level. When dose was constant, but delivered in a higher parasite concentration, higher infection prevalence and mortality resulted. One actinospore fish(-1) caused 57% infection and mortality in fish challenged in 0.5 1 of water, whereas 10 spores fish(-1) resulted in an average of 49% infection and mortality in 1 l challenges. This effect is most likely due to a higher encounter rate in the smaller water volume. Neither infection prevalence nor MDD was significantly different between large trout (84.9 g) and small trout (6.3 g). Chinook salmon did not become infected even when challenged with 5000 actinospores. One fatal infection occurred in coho salmon challenged with 1000 actinospores. This study confirms that even low doses of C. shasta cause severe infection in highly susceptible fish, describes the dose response on MDD, and demonstrates that parasite concentration influences infection prevalence.

Comparison of the susceptibility of brown trout ( Salmo trutta) and four rainbow trout ( Oncorhynchus mykiss) strains to the myxozoan Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD)

Differences in susceptibility to the myxozoan parasite Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD), between four strains of rainbow trout ( Oncorhynchus mykiss) and brown trout ( Salmo trutta) were evaluated. Fish were exposed to water enzootic for the parasite in the field for 5 days and were subsequently transferred to the laboratory. Relative parasite load was determined after 2, 3 and 4 weeks post-exposure (wpe) by quantitative real-time PCR (qPCR) of kidney samples and number of parasite stages was determined in immunohistochemical stained sections of kidney, liver and spleen tissues. According to qPCR results, the highest amount of parasite DNA per equal amount of host tissue at all time points was measured in brown trout. Two of the rainbow trout strains showed lower relative parasite load than all other groups at the beginning of the experiment, but the parasite multiplied faster in these strains resulting in an equal level of relative parasite load for all rainbow trout strains at 4 wpe. A weak negative correlation of fish size and parasite load was detected. Only in samples of a few fish, single stages of T. bryosalmonae were found in sections stained by immunohistochemistry impeding quantitative evaluation of parasite numbers by this method. The results indicate a differential resistance to T. bryosalmonae between the rainbow trout strains investigated and between rainbow trout and brown trout.

An evaluation of DVAqua®, a fully-fermented yeast culture, during long-term hatchery rearing of McConaughy strain rainbow trout

The addition of a proprietary, fully-fermented yeast Saccahromyces cerevisiae culture supplement (DVAqua®, Diamond V Mills, Cedar Rapids, IA, USA) was evaluated during long-term feeding of McConaughy strain rainbow trout Oncorhynchus mykiss. Beginning at initial feeding and continuing for 408 days of hatchery rearing, the trout received either a commercially-manufactured feed or the same feed containing 0.125 g kg−1 DVAqua. This study was conducted at a production level as part of normal (real-world) hatchery operations, with the fish periodically inventoried and moved into different rearing units. Although no rearing-tank replication occurred during the first 54 days of feeding, multiple tanks and raceways were used thereafter. Fish in rearing units receiving DVAqua supplementation exhibited less mortality, particularly during the earlier rearing stages. During the final 177 days of rearing in six raceways, DVAqua-fed McConaughy strain trout were significantly larger and had a significantly improved feed conversion ratio. The overall feed conversion ratio for the entire duration of the study was 1.17 in the fish receiving DVAqua supplementation compared to 1.21 in the control group. Despite the limitations of this study, the use of DVAqua is recommended for McConaughy strain rainbow trout and other less-domesticated, more difficult-to-rear salmonids.

In vivo exposure of susceptible and non-susceptible fish species to Myxobolus cerebralis actinospores reveals non-specific invasion behaviour

Due to controversial previous results, it has been unclear whether Myxobolus cerebralis (Myxosporea, Myxozoa) is able to specifically choose a salmonid host by selective attachment and penetration. Using a novel in vivo tracking assay that employs fluorescence staining of actinospore sporoplasms, we demonstrate a lack of host specificity of M. cerebralis actinospores during their initial invasion reactions. Fish were experimentally exposed to stained actinospores that could be detected as emitted sporoplasms in and on the fish integument of skin, gills and fins. There were no significant differences in the number of actively emerging sporoplasms found on epithelial surfaces of a susceptible and resistant strain of rainbow trout and common carp after experimental exposure. Numbers of parasite attachment rates to carp and trout gill tissue were also assessed using quantitative real-time PCR (qPCR). This method demonstrated that actinospore reactivity rate was not affected by the staining procedure. An even higher number of parasite stages was detected in carp than in trout gills. Subsequently, the ability of carp to lower the infection severity of susceptible rainbow trout by trapping the parasites under natural conditions was also investigated. Myxospore load was significantly reduced in hosts infected with actinospore samples that were preincubated with live carp. These results indicate the possibility of biological disturbance to the life cycle of the parasite in the wild by interceptor fish species as one measure to prevent whirling disease.

Subspecies‐informative SNP assays for evaluating introgression between native golden trout and introduced rainbow trout

We characterize 20 single nucleotide polymorphism assays for evaluating hybridization between native golden trout subspecies (Oncorhynchus mykiss aguabonita and O.m. whitei) and introduced rainbow trout strains. These assays utilize the 5'-nuclease reaction, facilitating high-throughput genotyping of many individuals and making them useful in quantifying and monitoring introgression and potentially applicable to studies of other O. mykiss groups. Minor allele frequency differentials (δq) among native and introduced rainbow groups ranged from 0 to 1, with an average differential of 0.75 for both subspecies aguabonita and whitei relative to the hatchery rainbow trout strain.

Cloning and tissue-specific expression of a .DELTA.-COP homologue in a freshwater and a brackish water-adapted strain of rainbow trout (Oncorhynchus mykiss)

In eukaryotic cells, intracellular transport is mediated by coated vesicular carriers. Coat proteins I (COPI) vesicles are involved in the retrograde transport from Golgi apparatus to the endoplasmic reticulum. The COPI complex is composed of ADP-ribosylation factor 1 and coatomer comprising seven subunits, termed alpha-zeta. We isolated and characterised a cDNA sequence from rainbow trout homolog to delta-subunit of COPI complex (delta-COP). Trout delta-COP gene encodes a protein of 509 aa including a characteristic Mu homology domain. Searches at the Ensemble Genome browser identified three additional teleostean delta-COP-like sequences from pufferfish, rice fish, and stickleback. Sequence identity of piscine delta-COP protein sequences is greater than 84%. Moreover, a phylogenetic analysis indicates that delta-COP protein sequences are strongly conserved among vertebrate species. delta-COP homologue is ubiquitously expressed in trout tissues. Quantitative Real-Time RT-PCR revealed that delta-COP is differentially expressed in liver and gill tissue of two rainbow trout strains, the freshwater strain STEELHEAD and the brackish water-adapted strain BORN.

Susceptibility of whirling disease (WD) resistance and WD susceptible strains of rainbow trout Oncorhynchus mykiss to Tetracapsuloides bryosalmonae, Yersinia ruckeri and viral haemorrhagic septicaemia virus

The focus of this work was to examine the susceptibility of a German rainbow trout strain (H) along with a North American strain (TL, which is highly susceptible to whirling disease) to three pathogens: the myxozoan parasite Tetracapsuloides bryosalmonae, which causes proliferative kidney disease (PKD), the bacterium Yersinia ruckeri, which causes enteric red mouth disease (ERM) and VHS virus, which is the causative agent of viral haemorrhagic septicaemia. Exposure to T. bryosalmonae was conducted under field conditions for 6 days in a hatchery long known to be endemic for the parasite. Fish were then transferred to our wet laboratory and held under controlled conditions until the end of the experiment at 16 weeks. Infection trials with Y. ruckeri and viral haemorrhagic septicaemia virus took place under controlled laboratory conditions, and lasted 21 days.Infections were confirmed by observation of clinical signs, histology and PCR, for all the pathogens investigated. For ERM, an additional bacteriological examination was carried out and for VHS; viral infection was confirmed by cell culture. At least one of these methods confirmed infection in all fish that died following challenges. The German strain H was found to have similar susceptibility as that of the American strain TL to all three pathogens investigated; there were no significant differences in the course of the diseases, clinical signs or mortality.

Genetic characterisation of farmed rainbow trout in Norway: intra- and inter-strain variation reveals potential for identification of escapees

BackgroundThe rainbow trout (Oncorhynchus mykiss) is one of the most important aquaculture species in the world, and Norway is one of the largest producers. The present study was initiated in response to a request from the Norwegian police authority to identify the farm of origin for 35 escaped rainbow trout captured in a fjord. Eleven samples, each consisting of approximately 47 fish, were collected from the three farms operating in the fjord where the escapees were captured. In order to gain a better general understanding of the genetic structure of rainbow trout strains used in Norwegian aquaculture, seven samples (47 fish per sample) were collected from six farms located outside the region where the escapees were captured. All samples, including the escapees, were genotyped with 12 microsatellite loci.ResultsAll samples displayed considerable genetic variability at all loci (mean number of alleles per locus per sample ranged from 5.4–8.6). Variable degrees of genetic differentiation were observed among the samples, with pair-wise FST values ranging from 0–0.127. Self-assignment tests conducted among the samples collected from farms outside the fjord where the escapees were observed gave an overall correct assignment of 82.5%, demonstrating potential for genetic identification of escapees. In the "real life" assignment of the 35 captured escapees, all were excluded from two of the samples included as controls in the analysis, and 26 were excluded from the third control sample. In contrast, only 1 of the escapees was excluded from the 11 pooled samples collected on the 3 farms operating in the fjord.ConclusionConsiderable genetic variation exists within and among rainbow trout strains farmed in Norway. Together with modern statistical methods, this will provide commercial operators with a tool to monitor breeding and fish movements, and management authorities with the ability to identify the source of escapees. The data generated in this study were used by the Norwegian police to initiate an investigation of the company operating the three farms in the fjord where escapees were observed.

Population genetic structure and ancestry of Oncorhynchus mykiss populations above and below dams in south-central California

Genetic analyses of coastal Oncorhynchus mykiss, commonly known as steelhead/rainbow trout, at the southern extreme of their geographic range in California are used to evaluate ancestry and genetic relationships of populations both above and below large dams. Juvenile fish from 20 locations and strains of rainbow trout commonly planted in reservoirs in the five study basins were evaluated at 24 microsatellite loci. Phylogeographic trees and analysis of molecular variance demonstrated that populations within a basin, both above and below dams, were generally each other’s closest relatives. Absence of hatchery fish or their progeny in the tributaries above dams indicates that they are not commonly spawning and that above-barrier fish are descended from coastal steelhead trapped at dam construction. Finally, no genetic basis was found for the division of populations from this region into two distinct biological groups, contrary to current classification under the US and California Endangered Species Acts.

Petri Dish Incubation of Eyed Eggs from Rainbow Trout and Splake

AbstractFour experiments were conducted from 2004 to 2006 to evaluate different protocols for incubating eyed eggs of salmonids in petri dishes. In the first two experiments, which used eyed eggs from Erwin strain rainbow trout Oncorhynchus mykiss or splake (lake trout Salvelinus namaycush ×brook trout S. fontinalis), dishes were loaded at either 10 or 20 eggs/dish and incubated at 10°C. Water changes occurred every 3 or 7 d until complete hatch; for each species, one group of dishes received no water change. Survival to hatch was not affected by the number of eggs per dish or the frequency of water changes in either species. However, in experiments 1 and 2, hatch was significantly earlier in the dishes containing 20 eggs than in dishes containing 10 eggs. In the last two experiments, 15 eyed eggs from Shasta or McConaughy strain rainbow trout were incubated at either 10°C or 12°C; the water was changed every 3 d or not at all. Shasta strain eggs exhibited no significant difference in survival or time to hatch between any of the treatments. For McConaughy strain eyed eggs, survival to hatch was significantly greater at 10°C than at 12°C, but water change treatment did not affect survival. No significant differences in time (d) to complete hatch were observed between temperature treatments or between water change regimes. To successfully mimic vertical‐flow incubation of eyed salmonid eggs in petri dishes, we recommend a density of no more than 15 eggs/dish; no water change is needed at a temperature of 10°C. Daily removal of dead eggs and hatched fry is also required.

Digestibility in selected rainbow trout families and relation to growth and feed utilisation

Experiments have been carried out aimed at clarifying variations in the digestibility of dietary nutrients in rainbow trout families and studying how differences in digestibility may be related to growth and feed utilisation at various growth rates. The digestibility of protein, lipid, carbohydrates (nitrogen-free extracts, NFE) and dry matter was analysed in two experiments involving eight rainbow trout families (Ab, Ba, Cd, Dc (first study); V, X, Y, Z (second study)). In the first experiment rainbow trout were reared for 128 days at 13.0C, and in the second experiment, they were reared for 84 days at 16.8C. In both experiments, the fish were fed ad libitum and reared from an initial weight of 70-100 g to a final weight of 500-700 g. When the fish reached a weight of approxi- mately 200 g, some individuals were moved to another experimental system in which the digestibility of protein, lipid, nitrogen-free extracts and dry matter was measured. Taken as a whole, our results indicate that selective breeding still offers a large potential for improved growth and feed utilisation in rainbow trout strains. In the first study, family Dc showed a higher specific growth rate (SGR) than the other three families (P \ 0.05), and family Ba showed a lower feed conversion ratio (FCR) than family Ab (P \ 0.05); there were no observed differences in digestibility despite some differences in growth. In the second study, family Y grew faster than all of the other families (P \ 0.05), and family Z grew faster than families V and X (P \ 0.01). A comparable pattern was seen for FCR, with family Y utilising feed better than family V (P \ 0.05), and families V, Y and Z performing better than family X (P \ 0.001). Protein digestibility was higher in the two fastest growing families (Y and Z) than in the slower growing family X (P \ 0.05), while lipid digestion was higher in family Y than in family V (P \ 0.05). A comparison of the results from both experiments revealed that protein digestibility in particular was closely

Family growth response to fishmeal and plant-based diets shows genotype × diet interaction in rainbow trout ( Oncorhynchus mykiss)

The ability of rainbow trout to efficiently utilize plant-based diets for growth and the genetic variation for that trait have not been thoroughly examined. In this study, growth of a pedigreed population from the commercial Kamloop strain was assessed while feeding both plant-based and traditional fishmeal-based diets from initiation of feeding to termination of the growth trial at an average body weight of 600 g. Both fish oil (5.00%) and soybean oil (8.43%) were included in the plant-based diet, and only fish oil was used in the fishmeal diet (10.10%). Ninety-five (92 informative) full-sib families nested within 47 (46 informative) half-sib families were reared in a common environment. Parentage assignment was performed on approximately 1000 fish fed each diet using eight microsatellite markers chosen for non-duplication, a minimum of five alleles with no known null alleles, at least 50% heterozygosity, and unambiguous scoring. Progeny were assigned to parental pairs via two allocation programs, PAPA and FAP, to increase accuracy and to test efficiency. The fish fed the fishmeal/oil diet were approximately 8% larger than the fish fed the plant-based diet ( P < 0.05). A significant genotype × diet effect was detected. The variance component for this effect accounted for 5% of the sum of the variance components for all the random effects. The genetic correlation for growth on the two diets was 0.73 ± 0.13, with a heritability of 0.31 ± 0.07 on the plant diet and 0.32 ± 0.07 on the fishmeal diet. We conclude that substantial genetic variation for utilizing plant-based diets containing soybean meal and oil exists in this widely used commercial rainbow trout strain.

Discovery of genes implicated in whirling disease infection and resistance in rainbow trout using genome-wide expression profiling

BackgroundWhirling disease, caused by the pathogen Myxobolus cerebralis, afflicts several salmonid species. Rainbow trout are particularly susceptible and may suffer high mortality rates. The disease is persistent and spreading in hatcheries and natural waters of several countries, including the U.S.A., and the economic losses attributed to whirling disease are substantial. In this study, genome-wide expression profiling using cDNA microarrays was conducted for resistant Hofer and susceptible Trout Lodge rainbow trout strains following pathogen exposure with the primary objective of identifying specific genes implicated in whirling disease resistance.ResultsSeveral genes were significantly up-regulated in skin following pathogen exposure for both the resistant and susceptible rainbow trout strains. For both strains, response to infection appears to be linked with the interferon system. Expression profiles for three genes identified with microarrays were confirmed with qRT-PCR. Ubiquitin-like protein 1 was up-regulated over 100 fold and interferon regulating factor 1 was up-regulated over 15 fold following pathogen exposure for both strains. Expression of metallothionein B, which has known roles in inflammation and immune response, was up-regulated over 5 fold in the resistant Hofer strain but was unchanged in the susceptible Trout Lodge strain following pathogen exposure.ConclusionThe present study has provided an initial view into the genetic basis underlying immune response and resistance of rainbow trout to the whirling disease parasite. The identified genes have allowed us to gain insight into the molecular mechanisms implicated in salmonid immune response and resistance to whirling disease infection.

Microhabitat selection of Gyrodactylus salaris Malmberg on different salmonids

The microhabitat selection of the ectoparasite Gyrodactylus salaris (Laerdalselva strain, Norway) was investigated concurrently with studies on the parasite population growth on five strains of Atlantic salmon, Salmo salar L., and a strain of Danish rainbow trout, Oncorhynchus mykiss (Walbaum). The salmon used were hatchery-reared parr of East Atlantic strains [River Conon (Scotland), River Storå (western Denmark) and River Atran (western Sweden)] and Baltic strains [Lule and Ume (eastern Sweden)]. The location and numbers of parasites were recorded on anaesthetized fish once a week from week 0 to week 8. The mean abundance of G. salaris steadily increased to high levels on the River Conon, Storå and Atran strains until the end of the experiment. The mean abundance of G. salaris on the two Baltic strains (River Lule älv and River Ume älv) initially increased but after 4-7 weeks the growth of the parasite infrapopulations decreased markedly. The Danish rainbow trout strain showed the lowest abundances of all the fish species and strains. Gyrodactylus salaris preferentially selected the fins and head region when colonising the hosts (all species and strains). Increasing percentages of G. salaris on the tail fins of the East Atlantic strains and rainbow trout were found during the course of infection, whereas the two Baltic salmon strains experienced a decreasing percentage of parasites in this microhabitat.