Strains Of Rainbow Trout Research Articles

Intra-strain dioxin sensitivity and morphometric effects in swim-up rainbow trout ( Oncorhynchus mykiss)

Inter and intra-specific differences in sensitivity of early life stage salmonids to 2,3,7,8-TCDD exposure have been reported, but intra-strain differences have not been found in the literature. Our results indicate that intra-strain variability in terms of embryo mortality (LD50) is small in Eagle Lake strain of rainbow trout, LD50 values ranging from 285 to 457 pg TCDD egg g −1. These results confirm Eagle Lake as a less sensitive strain within rainbow trout, and do not indicate overlap with reported LD50 values for brook or lake trout. Our results also demonstrate that although generalized edema in regions including the yolk-sac are frequently associated with mortality following dioxin exposure, not all edematous fish die. We detected dose-dependent decreases in cranial length, eye diameter, mass, and total length ( P<0.05) in viable swim-up rainbow trout. These effects are presumed to indicate more subtle dose-dependent disruptions of the viteline vein vasculature and, therefore, in access to energy sources. A tendency for dose-dependent decrease in liver glycogen reserves concurred with previous results on salmonids and with the well described TCDD-induced alterations in intermediate metabolism of rats and chicken embryos (wasting syndrome). This syndrome could be contributing to the reduced growth that we observed.

Growth Rate, Maturation Level and Flesh Quality of Three Strains of Large Rainbow Trout (Oncorhynchus Mykiss) Reared in Estonia

Three all-female strains of large rainbow trout imported to Estonia (Danish, Finnish and Donaldson strain) were evaluated in a communal rearing experiment in tanks. The fish had been reared on different fish farms before the experiment started and they had an initial weight of 400–500 g. There were no significant genetic differences between the investigated strains on the basis of three allozyme loci. The total weight gain of the strains during the trial was similar but differences were revealed between seasons. The growth rate of the Finnish trout was high during the first autumn but decreased during the second summer of the trial, probably due to infestation by eye fluke Diplostomum sp. The strains differed in the percentage of immature fish and in the level of gonad development at the age of 2.5–3 years. The Donaldson strain had the highest number of immature fish of the studied strains. Mature females of the Finnish strain had the smallest gonads but also the lowest percentage of immature fish. The level of maturation was the main factor determining the quality – slaughter yield and flesh color.

Genetic variation measured by microsatellites among three strains of domesticated rainbow trout (Oncorhynchus mykiss, Walbaum)

Genetic variation fuels selective change in natural and captive populations. In establishing a broodstock for selective improvement, the level of genetic diversity is an important consideration because it provides an indication of the scope for selective progress. Three domesticated strains of rainbow trout, Oncorhynchus mykiss (Walbaum), were examined at nine polymorphic microsatellite loci to assess detectable levels of allelic diversity and heterozygosity within and differentiation among the strains. A total of 126 alleles were observed to segregate into unique multilocus genotypes for each of the 152 individuals assayed. There was an average heterozygosity of 71.5% at these nine loci, and an average of 14 alleles at a locus. Each locus was represented by alleles unique to at least two of the three strains. Deviations from Hardy–Weinberg expectations of genotype frequencies were detected in each strain. Subsequent analysis indicated sub-structuring within strains leading to Wahlund effects that caused these deviations. Significant differences in genotype frequencies and pairwise FST values demonstrated that all strains were unique. The overall FST of 0.089 provides additional evidence of unique genetic diversity present in each strain, and agrees well with the degree of genetic variation found in rainbow trout across broad geographical ranges. The genetic diversity contributed by each population suggests that there is greater scope for selective improvement of numerous traits within a synthetic strain combining these three strains than within any individual strain.

Relatedness determination in the absence of pedigree information in three cultured strains of rainbow trout ( Oncorhynchus mykiss)

We evaluate the utility of a relatedness estimator ( r) as a tool for inbreeding avoidance in three aquaculture strains of rainbow trout ( Oncorhynchus mykiss) that show different amounts of genetic variation. The predicted distributions of r values for unrelated, half-sib and full-sib individuals based on population allele frequencies at 11–13 microsatellite loci were compared to those obtained from the genotypes of known parents. In two of the three strains, the r distributions derived from simulated progeny of known parents were significantly lower than those predicted using pairs of individuals created from strain-specific allele frequencies. This was most pronounced for the strain with the lowest average number of alleles per locus and derived from a very limited number of founders. The net result of these left shifts in the distributions is an underestimation of relatedness. In contrast, the third strain showed a more modest but significant right shift for the curves derived from the simulated progeny. The result of the right shift would be a reduction in the amount of related pairs assigned as unrelated for a given value of r. Thus, the probability of assigning related pairs as unrelated will increase markedly in aquaculture populations with histories of inbreeding and genetic bottlenecks.

Effects of Partial Tank Covers on the Growth of Juvenile Feral Rainbow Trout during Hatchery Rearing

AbstractPartial tank covers were evaluated for their effects on the growth of juvenile feral McConaughy strain rainbow trout Oncorhynchus mykiss during hatchery rearing. Trout were reared in 1999 and 2000 in circular tanks that were either completely open on top or partially (29%) covered. Trout reared in tanks with partial covers were 93 mm long at the end of 55 d of rearing in 1999, which was significantly longer than the 88‐mm mean length of trout reared in uncovered tanks. Total lengths were also significantly different after 34 d of rearing in 2000: 81 mm for fish from partially covered tanks and 78 mm for fish from open tanks. The total weight gains of fish per tank were significantly greater (23.9 versus 22.7 kg) and feed conversions were significantly better (0.83 versus 0.87) in partially covered tanks in 1999. In 2000, the total weight gain of fish per tank was 15.4 kg in tanks with partial covers and 13.5 kg in uncovered tanks, and the respective feed conversions were 0.90 and 1.05. However, neither weight gain nor conversion was significantly different in 2000. No significant differences in percent mortality were observed in fish reared with or without partial covers.

Determination of Smoltification Status in Juvenile Migratory Rainbow Trout and Chinook Salmon in Minnesota

Abstract The progress of smoltification was quantified with an enzyme assay (gill sodium-potassium-activated adenosine triphosphatase, or “Na+, K+-ATPase,” activity) in nonnative populations of migratory salmonines that are stocked or naturally spawned in Minnesota tributaries of Lake Superior. This information was needed to develop stocking strategies that would maximize imprinting at intended locations and to determine the causes and consequences of early emigration in stream-reared fish. Species and strains tested included (1) chinook salmon Oncorhynchus tshawytscha during hatchery rearing and after stocking, (2) two strains of O. mykiss—steelhead (naturalized) and a Kamloops (hatchery) strain of migratory rainbow trout—during hatchery rearing and after stocking, and (3) stream-reared steelhead emigrants captured in smolt traps. The ATPase activity level that distinguished smolts from nonsmolts was 11 μmol Pi · (mg protein)−1 · h−1 for chinook salmon and 10 μmol Pi · (mg protein)−1 · h−1 for all groups...

Effect of tributyltin on trout blood cells: changes in mitochondrial morphology and functionality

The aquatic environment is the largest sink for the highly toxic organotin compounds, particularly as one of the main sources is the direct release of organotins from marine antifouling paints. The aim of this study was to investigate the mitochondrial toxicity and proapoptotic activity of tributyltin chloride (TBTC) in teleost leukocytes and nucleated erythrocytes, by means of electron microscopy investigation and mitochondrial membrane potential evaluation, in order to provide an early indicator of aquatic environmental pollution. Erythrocytes and leukocytes were obtained from an inbred strain of rainbow trout ( Oncorhynchus mykiss). Transmission electronic micrographs of trout red blood cells (RBC) incubated in the presence of TBTC at 1 and 5 μM for 60 min showed remarkable mitochondrial morphological changes. TBTC-mediated toxicity involved alteration of the cristae ultrastructure and mitochondrial swelling, in a dose-dependent manner. Both erythrocytes and leukocytes displayed a consistent drop in mitochondrial membrane potential following TBTC exposure at concentrations >1 μM. The proapoptotic effect of TBTC on fish blood cells, and involvement of mitochondrial pathways was also investigated by verifying the release of cytochrome c, activation of caspase-3 and the presence of “DNA laddering”. Although mitochondrial activity was much more strongly affected in erythrocytes, leukocytes incubated in the presence of TBTC showed the characteristic features of apoptosis after only 1 h of incubation. Longer exposures, up to 12 h, were required to trigger an apoptotic response in erythrocytes.

Hormone profile in fast- and slow-growing strains of rainbow trout (Oncorhynchus mykiss) in response to nutritional state

The present study reports the hormone profile [growth hormone (GH) and thyroid hormones] in a fast- and slow-growing strain of rainbow trout under different feeding regimes. An examination as to whether growth rate could be related to the endogenous levels of these growth-promoter hormones was also undertaken. Fish were fed to satiation to establish routine feeding behaviour; others were submitted to a restricted ration level (2% of body weight) to nullify the feed intake effect, thereby allowing a comparison of the general metabolism of the fish, over a period of 16 weeks. Finally, fish were submitted to a 30-day fasting period, which functioned as a test to amplify the capacity of the animals to maintain high levels of circulating hormones. Differences in growth rate between the two rainbow trout strains, when fed to satiation, could not be associated with differences in hormonal status (pituitary and plasma GH, plasma T 3 and T 4 ). Nonetheless, fish of the fast-growing strain exhibited significantly higher circulating GH values than slow-growing fish, after the fasting period. Additional studies on both the thyroid hormones and GH receptor systems, and the cellular response to these hormones are warranted to further characterize this aspect of the endocrine regulation of body growth in the two rainbow trout strains.

Susceptibility of two strains of rainbow trout (one with suspected resistance to whirling disease) to Myxobolus cerebralis infection.

The susceptibility of 2 strains of rainbow trout Oncorhynchus mykiss, 1 from North America (TL) and 1 from Germany (GR), to Myxobolus cerebralis (the cause of salmonid whirling disease) was assessed following exposure to the infectious stages (triactinomyxons). Two laboratory experiments were conducted with age-matched rainbow trout of each strain. At the beginning of the study, the 2 trout strains were aged ca. 570 degree-days in Expt 1, and ca. 999 degree-days in Expt 2. In both experiments, replicate groups of each trout strain were exposed to 10, 100, 1000 or 10000 triactinomyxons (TAMs) fish(-1) for 2 h. The fish were then held in aquaria receiving 15 degrees C well-water. Severity of infection was evaluated 5 mo after exposure by presence of clinical signs (whirling and/or black tail), prevalence of infection, severity of microscopic lesions, and spore counts. Clinical signs of whirling disease were evident only in the younger fish exposed in Expt 1: These occurred first among TL rainbow trout at the highest dose at 6 to 7 wk post exposure and then 2 wk later in fish at the 1000 TAMs dose. Black tail was also observed among GR rainbow trout at the 10000 TAMs dose only, but in fewer fish. The prevalence of infection, spore numbers, and severity of microscopic lesions due to M. cerebralis among GR rainbow trout were less at all doses compared to TL rainbow trout. Risk of infection analyses showed that TL rainbow trout were more prone to infection at the lower doses than GR trout. Mean spore counts were consistently (10- to 100-fold) less in GR than TL trout at doses of 1000 TAMs or lower. Microscopic lesions increased with increasing dose in both strains of rainbow trout. The mechanisms underlying the greater resistance of the GR strain to M. cerebralis infections are unknown, but are under investigation as part of a long-term project to determine the basis for resistance and susceptibility of salmonid fishes to whirling disease.

Mass isolation of primordial germ cells from transgenic rainbow trout carrying the green fluorescent protein gene driven by the vasa gene promoter.

Mass isolation of live primordial germ cells (PGCs) was demonstrated for the first time in ectothermal vertebrates. To establish a stem cell-mediated gene transfer system in fish, a stem cell line that retains the ability to develop into gametes is necessary. PGCs are well suited for use as the initial material for such a stem cell line. We established transgenic rainbow trout (Oncorhynchus mykiss) strains carrying the green fluorescent protein (GFP) gene driven by a rainbow trout vasa-like gene (RtVLG) promoter/enhancer. Because GFP expression was specific to the PGCs, PGCs were successfully visualized in all developmental stages examined. Isolated genital ridges containing GFP-labeled PGCs were enzymatically dissociated. To isolate PGCs from the complex pools of dissociated genital ridges, GFP-labeled cells were sorted by flow cytometry. The sorted GFP-positive cells were large and round with a large nucleus, typical characters of PGC morphology. The expression of RtVLG was detected only in the GFP-positive cell population, confirming that these cells were PGCs. This simple and efficient technique to purify a large number of viable PGCs opens the way for establishing a stem cell line, which can differentiate into the germline. The purified PGCs would also be a novel tool for cellular and molecular study of vertebrate germline stem cells.

Detection of Visible Implant Elastomer in Fingerling and Yearling Rainbow Trout

Visible implant elastomer (VIE) was evaluated for marking yearling rainbow trout Oncorhynchus mykiss. The rate of tag detection after the yearlings had been at large for 35 months was also compared with the detection rate found in a subsequent year-class that had been marked as fingerlings and had been at large for 29 months. Fish were marked in the postocular adipose eyelid tissue and on the ventral surface of the lower jaw and examined in the dark under ultraviolet light. Detection rates for both year-classes ranged from 29% to 33%, based on the proportion of fish with two detectable marks. Because the marks were not easily recognized, we believe the detection rates were overestimated. We conclude that detection of VIE at the sites we chose was problematic for the strain of rainbow trout we marked. More favorable long-term detection rates in other species suggest that poor detection rates may be unique to heavily pigmented strains of rainbow trout.

Differences in MHC class I genes between strains of rainbow trout ( Oncorhynchus mykiss)

In rainbow trout there is only one dominant classical MHC class I locus, Onmy-UBA, for which four very different allelic lineages have been described. The purpose of the present study was to determine if Onmy-UBA polymorphism could be used for strain characterisation. This was performed by lineage-specific PCR investigation of 30 fish, each of the Nikko and Donaldson strains, and by sequence analysis of 25 of the amplified DNA fragments. Two new MHC class I lineages were detected in addition to the four previously described lineages, thus six distinct lineages were observed within the fish examined (Sal-MHCIa*A–F). The distribution of lineages appeared to be strain-specific. For example, the lineage Sal-MHCIa*A was very common in the Nikko strain but could not be detected in the Donaldson strain. Analysis of MHC class I variation may help to elucidate relationships between strains and the roles of MHC alleles in disease resistance.

Comparison of growth performance, immunological response and genetic diversity of five strains of rainbow trout ( Oncorhynchus mykiss)

The domestication of rainbow trout, Oncorhynchus mykiss, has led to the development of distinguishable isolated populations. In this study, five different strains of rainbow trout from the Northwest, USA were examined for variability in growth, immunological response, and genetic diversity. Growth rates for the different strains were monitored and compared for 28 weeks, with the animals fed at a fixed rate or to apparent satiation. Feed conversion ratios (FCR), specific growth rates (SGR), and thermal-unit growth coefficients (TGC) for the entire period were calculated for each of the strains. The different strains were also evaluated immunologically with infectious hematopoietic necrosis virus (IHNV), and their post-immunization antibody neutralization titers were monitored for a period of 12 weeks. Using microsatellites, the genetic variability between the strains was examined from a representational sample of the population of each strain. Fastest growing strains grew to a set weight of 350 g more rapidly regardless of whether they were fed at a fixed rate or to apparent satiation. These faster growing strains also exhibited a lower FCR and higher SGR and TGC values, and higher percentage protein retention. The IHNV neutralization titers for the strains varied considerably with one high humoral response group and one low humoral response group. The remaining three strains clustered approximately midway between the other two. Genetically, the strains exhibited a pattern of wide divergence, with only 9 common alleles out of a total of 89 different alleles between the five strains. As expected, commercial aquaculture strains reared locally were genetically more similar, and strains that have undergone intense selection tended to have a strong correlation between reduced genetic variability, FCR, and SGR as compared to noncommercial strains.

Feeding behaviour of fast-and slow-growing strains of rainbow trout, Oncorhynchus mykiss (Walbaum), during first feeding

Feeding behaviour of fast-and slow-growing strains of rainbow trout, <i>Oncorhynchus mykiss</i> (Walbaum), during first feeding

A Comparison of Susceptibility toMyxobolus cerebralisamong Strains of Rainbow Trout and Steelhead in Field and Laboratory Trials

Abstract Three strains of rainbow trout and steelhead Oncorhynchus mykiss were evaluated for the presence of whirling disease in field and laboratory trials. In the field exposures, fingerling Salmon River steelhead and Cayuga Lake and Randolph strains of rainbow trout were placed in wire cages in an earthen, stream-fed pond in New York State that was known to harbor Myxobolus cerebralis. Control fish were held at another hatchery that was free of whirling disease. In the controlled trials at the National Fish Health Research Laboratory, fingerling steelhead and Cayuga Lake and Mount Lassen rainbow trout were exposed to triactinomyxons at low (200 triactinomyxons/fish) or high (2,000 triactinomyxons/fish) levels for 2 h. Controls of each group were sham-exposed. Following an incubation period of 154 d for laboratory trials and 180 d for field trials, cranial tissue samples were taken for spore enumeration (field and laboratory trials) and histological analyses (laboratory only). Clinical signs of disease,...

A genetic analysis of the London strain of rainbow trout.

The London strain of rainbow trout (Oncorhynchus mykiss) was created by interbreeding three other strains of rainbow trout and therefore was expected to have higher levels of genetic variation than other strains of rainbow trout. We examined 129 London strain rainbow trout from Indiana by allozyme electrophoresis to assess levels of genetic variation and to examine the relationship between the London strain and other hatchery strains. When using the same loci to compare with other hatchery strains the London strain showed levels of genetic variation within the range of other hatchery strains: mean heterozygosity of 0.053 (0.031-0.099), 1.27 (1.20-1.60) alleles per locus and 20.0% (20.0-40.0%) of the loci were polymorphic. The London strain is somewhat distinct from other hatchery strains (D=0.009-0.072), in part because of the high frequency of the sIDHP*40 allele.

Feeding behaviour of fast- and slow-growing strains of rainbow trout,Oncorhynchus mykiss(Walbaum), during first feeding

The development of feeding behaviour in two rainbow trout strains and their hybrid was compared at the transition from endogenous nutrition to exogenous feeding. After 60 min of acclimatization, the swimming pattern, spatial distribution, agonistic behaviour and snapping of fish were quantified by making 5-min observations on groups of five fish. Behavioural patterns were recorded in four replicate groups per treatment, before and after the introduction of dry trout feed or Artemia nauplii (actometric tests) or extracts of these (olfactometric tests). Fish of the slow growing strain were less active than those of the other two strains. Greater swimming activity observed in the fish of the fast growing strain was associated with more rapid feeding and a higher number of snapping responses. Such behavioural precocity is of interest because it could provide the basis for the growth differences between the fast and slow growing strains.

Development and characterization of DNA sequence OmyP9 associated with the sex chromosomes in rainbow trout.

This work describes the construction and characterization of a sequence characterized amplified DNA region (SCAR DNA), designated OmyP9, that was derived from a RAPD marker associated with the sex chromosomes in rainbow trout. A RsaI restriction fragment length polymorphism in OmyP9 identifies variants A, B and C. We found six OmyP9 variant phenotypes - A, B, C, AB, BC and ABC, in 186 individuals of seven different rainbow trout strains. The patterns of inheritance of OmyP9 in 139 fingerlings from 10 crosses of three strains of rainbow trout were studied. The males had a greater representation of the A variant (93.3%) suggesting an association with the Y chromosome. All male fingerlings analysed inherited the A variant from their male parents. These results support the hypothesis that OmyP9 is located on the sex chromosomes of rainbow trout, and that for the males studied the A variant is located on the Y chromosome in a region close to sex determinants and/or in a sector where the genetic recombination between X and Y is restricted. The present evidence also supports our previous hypothesis that OmyP9 is organized as a tandem repeated sequence in the sex chromosomes of rainbow trout. We feel that the OmyP9 RsaI marker can be used for sex identification in crosses where it is possible to determine the phenotype of the parents.

Salmonids Resistant toCeratomyxa shastaAre Susceptible to Experimentally Induced Infections withMyxobolus cerebralis

Two strains of rainbow trout Oncorhynchus mykiss and one strain of steelhead (anadromous rainbow trout) previously shown to demonstrate resistance to the myxosporean pathogen Ceratomyxa shasta were found to be susceptible to experimentally induced infections with the myxosporean Myxobolus cerebralis. Laboratory exposures to waterborne infectious stages (triactinomyxons) of M. cerebralis of both strains of rainbow trout and the steelhead resulted in clinical signs of whirling disease, including the characteristic tail chasing and black tail, approximately 42–49 d after exposure at a water temperature of 15°C. At 5 months postexposure, the severity of microscopic lesions and spore concentrations in the head cartilage of all salmonids resistant to C. shasta were evaluated. The Iron Gate steelhead and the Pit River rainbow trout that were resistant to C. shasta had lesion scores and spore counts similar to those of control rainbow trout known to be susceptible to C. shasta. Evidence of some resistance to M. cerebralis among the Deschutes River strain of rainbow trout was demonstrated by lower lesion scores and mean spore counts than were seen in the control rainbow trout strain. In general, however, the mechanisms of resistance that have developed among certain salmonid populations to one myxosporean, C. shasta, do not extend to protection or resistance to a second myxosporean, the causative agent of salmonid whirling disease.

Lack of Selection for Resistance to Whirling Disease among Progeny of Colorado River Rainbow Trout

Abstract We compared the resistance to whirling disease of two groups of Colorado River rainbow trout Oncorhynchus mykiss and a domestic strain of rainbow trout in a controlled laboratory challenge. These three groups represented the progeny of wild rainbow trout known to have recruited (1) during the early years of infestation by Myxobolus cerebralis of the Colorado River or (2) before the presence of M. cerebralis in the system and (3) the Erwin strain of rainbow trout. The severity of whirling disease in each group was dependent on the dose of triactinomyxons of M. cerebralis to which the fish were exposed. Microscopic lesions and spore counts both increased with increasing parasite dose. Survival of the progeny of Colorado fish that recruited before the presence of M. cerebralis in the system was significantly less than was that of the domestic fish exposed to 0 and 1,000 triactinomyxons/fish. The parents that recruited to the system before the presence of M. cerebralis were considerably older than we...