Body Weight Of Rainbow Trout Research Articles

Genomic selection models substantially improve the accuracy of genetic merit predictions for fillet yield and body weight in rainbow trout using a multi-trait model and multi-generation progeny testing

BackgroundIn aquaculture, the proportion of edible meat (FY = fillet yield) is of major economic importance, and breeding animals of superior genetic merit for this trait can improve efficiency and profitability. Achieving genetic gains for fillet yield is possible using a pedigree-based best linear unbiased prediction (PBLUP) model with direct and indirect selection. To investigate the feasibility of using genomic selection (GS) to improve FY and body weight (BW) in rainbow trout, the prediction accuracy of GS models was compared to that of PBLUP. In addition, a genome-wide association study (GWAS) was conducted to identify quantitative trait loci (QTL) for the traits. All analyses were performed using a two-trait model with FY and BW, and variance components, heritability, and genetic correlations were estimated without genomic information. The data used included 14,165 fish in the pedigree, of which 2742 and 12,890 had FY and BW phenotypic records, respectively, and 2484 had genotypes from the 57K single nucleotide polymorphism (SNP) array.ResultsThe heritabilities were moderate, at 0.41 and 0.33 for FY and BW, respectively. Both traits were lowly but positively correlated (genetic correlation; r = 0.24), which suggests potential favourable correlated genetic gains. GS models increased prediction accuracy compared to PBLUP by up to 50% for FY and 44% for BW. Evaluations were found to be biased when validation was performed on future performances but not when it was performed on future genomic estimated breeding values.ConclusionsThe low but positive genetic correlation between fillet yield and body weight indicates that some improvement in fillet yield may be achieved through indirect selection for body weight. Genomic information increases the prediction accuracy of breeding values and is an important tool to accelerate genetic progress for fillet yield and growth in the current rainbow trout population. No significant QTL were found for either trait, indicating that both traits are polygenic, and that marker-assisted selection will not be helpful to improve these traits in this population.

Identifying environmental variables explaining genotype-by-environment interaction for body weight of rainbow trout (Onchorynchus mykiss): reaction norm and factor analytic models

BackgroundIdentifying the relevant environmental variables that cause GxE interaction is often difficult when they cannot be experimentally manipulated. Two statistical approaches can be applied to address this question. When data on candidate environmental variables are available, GxE interaction can be quantified as a function of specific environmental variables using a reaction norm model. Alternatively, a factor analytic model can be used to identify the latent common factor that explains GxE interaction. This factor can be correlated with known environmental variables to identify those that are relevant. Previously, we reported a significant GxE interaction for body weight at harvest in rainbow trout reared on three continents. Here we explore their possible causes.MethodsReaction norm and factor analytic models were used to identify which environmental variables (age at harvest, water temperature, oxygen, and photoperiod) may have caused the observed GxE interaction. Data on body weight at harvest was recorded on 8976 offspring reared in various locations: (1) a breeding environment in the USA (nucleus), (2) a recirculating aquaculture system in the Freshwater Institute in West Virginia, USA, (3) a high-altitude farm in Peru, and (4) a low-water temperature farm in Germany. Akaike and Bayesian information criteria were used to compare models.ResultsThe combination of days to harvest multiplied with daily temperature (Day*Degree) and photoperiod were identified by the reaction norm model as the environmental variables responsible for the GxE interaction. The latent common factor that was identified by the factor analytic model showed the highest correlation with Day*Degree. Day*Degree and photoperiod were the environmental variables that differed most between Peru and other environments. Akaike and Bayesian information criteria indicated that the factor analytical model was more parsimonious than the reaction norm model.ConclusionsDay*Degree and photoperiod were identified as environmental variables responsible for the strong GxE interaction for body weight at harvest in rainbow trout across four environments. Both the reaction norm and the factor analytic models can help identify the environmental variables responsible for GxE interaction. A factor analytic model is preferred over a reaction norm model when limited information on differences in environmental variables between farms is available.

Genetics of Microenvironmental Sensitivity of Body Weight in Rainbow Trout (Oncorhynchus mykiss) Selected for Improved Growth

Microenvironmental sensitivity of a genotype refers to the ability to buffer against non-specific environmental factors, and it can be quantified by the amount of residual variation in a trait expressed by the genotype’s offspring within a (macro)environment. Due to the high degree of polymorphism in behavioral, growth and life-history traits, both farmed and wild salmonids are highly susceptible to microenvironmental variation, yet the heritable basis of this characteristic remains unknown. We estimated the genetic (co)variance of body weight and its residual variation in 2-year-old rainbow trout (Oncorhynchus mykiss) using a multigenerational data of 45,900 individuals from the Finnish national breeding programme. We also tested whether or not microenvironmental sensitivity has been changed as a correlated genetic response when genetic improvement for growth has been practiced over five generations. The animal model analysis revealed the presence of genetic heterogeneity both in body weight and its residual variation. Heritability of residual variation was remarkably lower (0.02) than that for body weight (0.35). However, genetic coefficient of variation was notable in both body weight (14%) and its residual variation (37%), suggesting a substantial potential for selection responses in both traits. Furthermore, a significant negative genetic correlation (−0.16) was found between body weight and its residual variation, i.e., rapidly growing genotypes are also more tolerant to perturbations in microenvironment. The genetic trends showed that fish growth was successfully increased by selective breeding (an average of 6% per generation), whereas no genetic change occurred in residual variation during the same period. The results imply that genetic improvement for body weight does not cause a concomitant increase in microenvironmental sensitivity. For commercial production, however, there may be high potential to simultaneously improve weight gain and increase its uniformity if both criteria are included in a selection index.

The relationship and the fecundity between the egg size and the body weight of rainbow trout (Oncorhynchus mykiss Walbaum, 1792) and brook trout (Salvelinus fontinalis Mitchil, 1814).

The relationship and the fecundity between the egg size and the body weight of rainbow trout (Oncorhynchus mykiss Walbaum, 1792) and brook trout (Salvelinus fontinalis Mitchil, 1814).

Estimation of additive and dominance genetic variances for body weight at harvest in rainbow trout, Oncorhynchus mykiss

Additive genetic, dominance genetic, and common environmental variance components were estimated for body weight at harvest for three populations of rainbow trout under selection for six generations in Norway. Six different models were studied by including all or different subsets of the following effects in an animal model: additive genetic ( A), parental dominance ( D), common environmental due to full-sibs ( CE) and inbreeding coefficient ( F) as a covariate. Variance components were estimated using the Average Information Restricted Maximum Likelihood (AIREML) method. In general, the results showed that estimates of additive genetic variance were inflated under the simple models ( A) and ( A+ F), and decreased remarkably under the more complex models such as ( A+ CE), ( A+ CE+ F), ( A+ D+ F), and ( A+ D+ CE+ F). The magnitude of the dominance variance ranged from 0 to 22% and the common environmental variance from 0% to 6% of the total phenotypic variance. The study confirmed the presence of a significant dominance genetic variance for harvest body weight in rainbow trout. However, the results indicate that the dominance and common environmental effects may be confounded in the present data.

Metabolic response to dietary phosphorus intake in rainbow trout ( Oncorhynchus mykiss)

The objectives of this study were to determine which indicators were most responsive to suboptimal phosphorus intake in fingerling rainbow trout, and to observe the magnitude of these changes over time. Fish with an initial mean weight of 1.8 g were hand-fed one of five semipurified wheat-gluten based diets containing between 0.23%–1.16% dietary phosphorus, or a fish meal control diet (1.8% P) for 8 weeks. Phosphorus, calcium and magnesium concentrations in whole body, skin (with scales), and plasma were measured bi-weekly. Alkaline phosphatase activity was determined in plasma and in a crude intestinal homogenate. There was no correlation between dietary phosphorus concentration and body weight of rainbow trout. Of all tissues and metabolites examined, skin was the most responsive to differences in dietary phosphorus concentration. Dietary treatment had a significant effect on the concentrations of ash, phosphorus, calcium and magnesium in rainbow trout skin at weeks 4 and 8. Whole body ash, phosphorus, calcium, and magnesium concentrations were also highly responsive to graded levels of dietary phosphorus at week 8. Rainbow trout fed suboptimal phosphorus diets had significantly lower plasma phosphorus concentrations and alkaline phosphatase activity, and significantly higher whole body lipid than those fed adequate phosphorus diets. Alkaline phosphatase activity of the intestinal homogenate was not significantly correlated with dietary phosphorus intake.

Genetic and environmental variation of body weight in rainbow trout ( Oncorhynchus mykiss)

Body weight data covering the period from birth year 1978 to 1986 from a selection experiment with rainbow trout conducted at the University of California at Davis were analyzed with regard to the genetic and environmental variation in three lines (Line C reproduced by random selection; Line E selected for egg size; Line Y selected for body weight at 364 days of age). Variance components for body weight from 168 to 364 days were estimated using a derivative-free restricted maximum likelihood algorithm under a single trait animal model. Heritability estimates were low, ranging from 0.03 to 0.13. The estimates for Line Y were lower than those for Line C and Line E, possibly a result of sampling error when the three lines were formed from a small common base population. The heritability estimates tended to increase with age; averaged over the three lines, the estimates were lowest at 168 days (0.05) and highest at 336 and 364days (0.10). Full-sib family effects caused by factors other than additive genetic effects were relatively large, ranging from 0.01 to 0.17 as a proportion of the phenotypic variance, and also increased with age, being lowest at 196 days (0.03) and highest at 364 days (0.14) averaged over the three lines. Both common environmental and non-additive genetic effects could contribute to this component. Common environmental effect may result from the competition for space between families owing to the particular rearing procedures used for the experiment. In addition, the different inbreeding levels among families may have increased the variation between families by reducing the expression of non-additive genetic effects to different degrees. The age trend of full-sib family effects on body weight may be a reflection of the accumulation of competition effect and the increase of non-additive genetic effect as the fish grew larger.

Selection experiments for improving “pan-size” body weight of rainbow trout ( Oncorhynchus mykiss)

Two generation selection experiments for improving pan-size body weight of rainbow trout were carried out in a series of four experiments including spring and autumn spawners. Each selection experiment consisted of a selection and a contemporary control line. Combined family selection was applied in all selection lines using pan-size body weight as the selection criterion. Comparisons of growth performance of selection and control lines included fattening of fish at two stocking densities. In general, responses under low density conditions were higher than those under high density conditions. After two generations, the highest significant response was obtained in line 4 with 32 g (deviation from control mean) or 27% at low density whereas at high density the response was only onefourth of this value. Averaged over all lines, realized heritability was 0.15. In general, positively correlated responses were found for rearing weight; however, greater changes in the ranking between rearing and fattening weight could be observed for a number of families. Till now, selection for fattening weight has not resulted in changes in the proportional weight of head and fins and has not altered carcass composition.

Simulation of Response to Selection for Body Weight in Rainbow Trout

Simulation of Response to Selection for Body Weight in Rainbow Trout

A genetic analysis of body weight and length in rainbow trout reared in seawater for 18 months

Data from four year-classes of raibow trout was analysed. The brood fish originally came from different Norwegian fish farms, but all are considered to belong to the same population. During the freshwater period each full-sib family was reared separately and each group was given as equal environmental conditions as possible. Fingerlings from each fullsib family were sampled and freeze-branded. At an age of one year fingerlings from each family were sampled and transported to different fish farms along the Norwegian coast. This paper deals with the traits body weight and length at slaughter after about 18 months in net cages in the sea. Fish farm × sire interaction was significant, but accounted for a relatively small part of the total phenotypic variance. It is concluded that genotype × farm interaction can be ignored when planning a selection programme for rainbow trout under Norwegian farming conditions. A significant interaction was found between sire and dam, implying the presence of non-additive genetic variation. The heritabilities for body weight and length estimated from sire components (year-class 1973, 1974 and 1975) were 0.17 and 0.23, respectively. The genetic correlation between body weight and length was close to unity. Genetic variation in body weight of rainbow trout is high, about three times as high as for body length. The heritabilities estimated for condition factor were small and none of the sire components were significant. It is concluded that the combination of weight and length used to calculate the K-factor has little genetic basis.

Carcinogenicity and Acute Toxicity of Dimethylnitrosamine in Rainbow Trout (Salmo gairdneri)23

Four-week-old rainbow trout (Salmo gairdneri) were fed diets containing 0, 3, 50, 200, 400, and 800 ppm dimethylnitrosamine (DMN) for 52 weeks. At the end of 52 weeks, the fish were fed a control diet without DMN for an additional 26 weeks. Samples were taken at 26, 52, and 78 weeks to determine tumor incidence. A dose-related carcinogenic response was established from these results, and an equation was derived to relate the level of the carcinogen to the hepatocellular carcinoma incidence. From a published dose-response study that used outbred Porton rats, a second equation was derived for comparison. Rats and trout were approximately equal in their sensitivity to DMN carcinogenesis. The median lethal dose after ip injection of DMN was 1,770 mg/kg body weight in rainbow trout. Relative to the range of 15-50 mg/kg body weight reported for several mammalian species, trout were resistant to the acute toxicity of DMN.