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ABSTRACT: This study determined the effect of genetic variation, feed deprivation, and insulin-like growth factor-I (IGF-I) on weight loss, plasma IGF-I and growth hormone, and indexes of protein degradation in eight full-sibling families of rainbow trout. After 2 wk of feed deprivation, fish treated with IGF-I lost 16% less (P < 0.05) wet weight than untreated fish. Feed deprivation increased growth hormone (P < 0.05) and decreased IGF-I (P < 0.05), but hormone levels were not altered by IGF-I. Plasma 3-methylhistidine concentrations were not affected by IGF-I but were decreased after 2 wk (P < 0.05) and increased after 4 wk (P < 0.05) of feed deprivation. In white muscle, transcript abundance of genes in the ubiquitin-proteasome, lysosomal, and calpain- and caspase-dependent pathways were affected by feed deprivation (P < 0.05). IGF-I prevented the feed deprivation-induced upregulation of MAFbx (F-box) and cathepsin transcripts and reduced abundance of proteasomal mRNAs (P < 0.05), suggesting that reduction of protein degradation via these pathways may be partially responsible for the IGF-I-induced reduction of weight loss. Family variations in gene expression, IGF-I concentrations, and weight loss during fasting suggest genetic variation in the fasting response, with considerable impact on regulation of proteolytic pathways. These data indicate that nutrient availability, IGF-I, and genetic variation affect weight loss, in part through alterations of proteolytic pathways in rainbow trout, and that regulation of genes within these pathways is coordinated in a way that supports a similar physiological response.
AJP Regulatory Integrative and Comparative Physiology 09/2009; 297(5):R1332-42. · 3.34 Impact Factor
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ABSTRACT: As a first step toward the genetic mapping of QTL affecting stress response variation in rainbow trout, we performed complex segregation analyses (CSA) fitting mixed inheritance models of plasma cortisol by using Bayesian methods in large full-sib families of rainbow trout. To date, no studies have been conducted to determine the mode of inheritance of stress response as measured by plasma cortisol response when using a crowding stress paradigm and CSA in rainbow trout. The main objective of this study was to determine the mode of inheritance of plasma cortisol after a crowding stress. The results from fitting mixed inheritance models with Bayesian CSA suggest that 1 or more major genes with dominant cortisol-decreasing alleles and small additive genetic effects of a large number of independent genes likely underlie the genetic variation of plasma cortisol in the rainbow trout families evaluated. Plasma cortisol is genetically determined, with heritabilities of 0.22 to 0.39. Furthermore, a major gene with an additive effect of -42 ng/mL (approximately 1.0 genetic SD) is segregating in this rainbow trout broodstock population. These findings provide a basis for designing and executing genome-wide linkage studies to identify QTL for stress response in rainbow trout broodstock and markers for selective breeding.
Journal of Animal Science 08/2009; 87(11):3490-505. · 2.10 Impact Factor
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ABSTRACT: Selective breeding of animals for increased innate resistance offers an attractive strategy to control disease in agriculture. However, this approach is limited by an incomplete knowledge of the heritability, duration, and mechanism(s) of resistance, as well as the impact of selection on the immune response to unrelated pathogens. Herein, as part of a rainbow trout broodstock improvement program, we evaluated factors involved in resistance against a bacterial disease agent, Flavobacterium psychrophilum. In 2005, 71 full-sibling crosses, weighing an average of 2.4 g, were screened, and resistant and susceptible crosses were identified. Naive cohorts were evaluated at 10 and 800 g in size, and most maintained their original relative resistant or susceptible phenotypes, indicating that these traits were stable as size increased >300-fold. During the course of these studies, we observed that the normalized spleen weights of the resistant fish crosses were greater than those of the susceptible fish crosses. To test for direct association, we determined the spleen-somatic index of 103 fish crosses; created high, medium, and low spleen-index groups; and determined survival following challenge with F. psychrophilum or Yersinia ruckeri. Consistent with our previous observations, trout with larger spleen indices were significantly more resistant to F. psychrophilum challenge; however, this result was pathogen-specific, as there was no correlation of spleen size with survival following Y. ruckeri challenge. To our knowledge, this is the first report of a positive association between spleen size and disease resistance in a teleost fish. Further evaluation of spleen index as an indirect measure of disease resistance is warranted.
The Journal of Immunology 04/2008; 180(6):4156-65. · 5.79 Impact Factor
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ABSTRACT: Although studies have established that exogenous growth hormone (GH) treatment stimulates growth in fish, its effects on target tissue gene expression are not well characterized. We assessed the effects of Posilac (Monsanto, St. Louis, MO), a recombinant bovine GH, on tissue transcript levels in rainbow trout selected from two high-growth rate and two low-growth rate families. Transcript abundance was measured in liver and muscle with the Genome Research in Atlantic Salmon Project (GRASP) 16K cDNA microarray. A selection of the genes identified as altered by the microarray and transcripts for insulin-like growth factors, growth hormone receptors (GHRs), and myostatins were measured by real-time PCR in the liver, muscle, brain, kidney, intestine, stomach, gill, and heart. In general, transcripts identified as differentially regulated in the muscle on the microarray showed similar directional changes of expression in the other nonhepatic tissues. A total of 114 and 66 transcripts were identified by microarray as differentially expressed with GH treatment across growth rate for muscle and liver, respectively. The largest proportion of these transcripts represented novel transcripts, followed by immune and metabolism-related genes. We have identified a number of genes related to lipid metabolism, supporting a modulation in lipid metabolism following GH treatment. Most notable among the growth-axis genes measured by real-time PCR were increases in GHR1 and -2 transcripts in liver and muscle. Our results indicate that short-term GH treatment activates the immune system, shifts the metabolic sectors, and modulates growth-regulating genes.
Physiological Genomics 03/2008; 32(3):380-92. · 2.73 Impact Factor
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ABSTRACT: The effects of growth hormone secretagogues (GHSs) on the teleost somatotropic axis are poorly understood, particularly with respect to insulin-like growth factor-I (IGF-I) and the IGF-binding proteins (IGFBPs). To assess the endocrine and orexigenic responses of rainbow trout (Oncorhynchus mykiss) to GHS treatment, animals were injected with human GHRH(1-29)-amide, KP-102 or rat ghrelin at 0, 1 or 10 pmol/g body mass. Feed intake was tested at 2 and 5 h post-injection and plasma levels of growth hormone (GH), IGF-I and the IGFBPs were determined at 3, 6 and 12 h post-injection. Feed intake was significantly elevated by all of the GHSs tested at both post-injection time points. All GHSs elevated plasma GH levels in a time-dependent manner. Plasma IGF-I levels were elevated by all GHSs at 3 h post-injection, whereas those animals treated with KP-102 and ghrelin exhibited depressions at 6 h. Four IGFBPs were identified in the plasma by western blotting. Levels of the 20 kDa IGFBP decreased over the sampling time. Levels of the 32 kDa IGFBP were significantly depressed by all GHSs tested. Levels of the 42 kDa IGFBP were significantly elevated by all GHSs tested. Plasma levels of the 50 kDa IGFBP was decreased in some treatment groups at 3 h, but elevated by 6 h in the ghrelin-treated groups and elevated in all treatment groups by 12 h post-injection. The endocrine and orexigenic responses demonstrate that GHSs influence the teleost neuroendocrine system beyond short-term actions (<3 h post-injection) on GH release and the responses of the IGFBPs to GHS treatment support this notion and clarify their identification as functional homologues to mammalian IGFBPs.
Comparative Biochemistry and Physiology - Part A Molecular & Integrative Physiology 04/2007; 146(3):390-9. · 2.23 Impact Factor
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ABSTRACT: The efficient use of feed for growth and meat production is important for all animal production industries including aquaculture. Residual feed intake (RFI) is an alternative measure of feed efficiency that has been widely used in livestock production. Residual feed intake was calculated as the difference between intake observed and intake predicted on the basis of a bioenergetics model; a low RFI indicates greater efficiency. Residual feed intake offers some advantages as a selection criterion for improving production efficiency over traditional feed efficiency statistics because it is not a ratio and it typically has a larger coefficient of variation. The RFI of individually reared rainbow trout progeny from six different genetic cross-types was examined for genetic variation. Proximate analysis and nitrogen retention were also evaluated to determine if differences in RFI correlate to differences in body composition and nutrient retention and varied by cross-type. Differences between cross-types indicated a genetic component for RFI, with the most efficient fish of approximately 160 g consuming 0.99 g less and inefficient fish consuming 0.05 g more feed per day than expected. Lower RFI was associated with higher growth rates (r=−0.38, P<0.05) and greater nitrogen retention (r=−0.82 P<0.001).
Aquaculture Research 04/2005; 36(7):704 - 711. · 1.20 Impact Factor
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ABSTRACT: A study was conducted to evaluate genotype × feed interactions in a commercial strain of rainbow trout (Oncorhynchus mykiss). Microsatellite DNA markers were used to determine the pedigree of the top 1% and bottom 1% of progeny in a large scale commercial growth trial of 24,000 rainbow trout from 20 full-sib families (20 dams × 10 sires in a nested mating design). The progeny were pooled at eyed stage and divided into 2 groups. Half of the fish from each family were fed a standard fishmeal-based diet and the other half was fed a plant protein (gluten)-based diet to determine the relative family rankings in each diet. The primary protein sources in the plant protein-based diet were corn gluten and wheat gluten meals. Krill was supplemented to this feed for the early life stages (starter, #1, #2, #3 crumbles), but was eliminated in the larger pellet sizes. Large genetic variation for growth was identified for both diets and the sire effect was found to be highly significant (P < 0.001). The family rankings were similar for both diets, which suggest that the fish that grow faster on fishmeal diet are likely to grow faster on plant protein-based diets, and therefore current commercial strains that exhibit superior growth should retain their improved performance if raised on gluten-based diets. Multiplexing microsatellite markers would further improve the efficiency of parentage assignment protocols in large-scale rainbow trout selection programs.
Aquaculture.
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ABSTRACT: 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.
Aquaculture.
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ABSTRACT: Genes within the major histocompatibility complex (MHC) are important for both innate and adaptive immune responses in mammals; however, much less is known regarding their contribution in teleost fishes. We examined the involvement of four major histocompatibility (MH) genomic regions in rainbow trout in resistance to the causative agent of bacterial coldwater disease (BCWD), Flavobacterium psychrophilum. Fish from the 2005 NCCCWA brood-year (71 full-sib families) were challenged with F. psychrophilum strain CSF 259-93. The overall mortality rate was 70%, with large variation in mortality between families. Disease resistance was quantified as post-challenge days to death. Phenotypic variation and additive genetic variation were estimated using mixed models of survival analysis. To examine association, eight microsatellite markers were isolated from MH gene-containing BAC clones and mapped onto the rainbow trout genetic linkage map. The parents and grandparents of the 2005 brood-year families were genotyped with these eight markers and another two markers tightly linked to the MH-IB region to assess the extent of linkage disequilibrium (LD) of MH genomic regions MH-IA, MH-IB, TAP1, and MH-II with survival post-challenge. MH-IB and MH-II markers were linked to BCWD survivability when data were analyzed by family. Tests for disease association at the population level substantiated the involvement of MH-IB, but not MH-II, with disease resistance. The impact of selective breeding for disease resistance on MH sequence variation is discussed in the context of aquaculture production.
Marine Biotechnology 10(4):429-37. · 3.43 Impact Factor
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ABSTRACT: Lysine is the second limiting amino acid in fish meal based diets, second only to methionine. However, little is known about lysine metabolism in rainbow trout (RBT). Therefore, lysine catabolism by the lysine α-ketoglutarate reductase (LKR) pathway was studied. Additionally, since genetically improved strains could influence fish production, these studies were performed in 4 distinct families of RBT. Two full-sibling families, differing in feed efficiency, were selected from each of 2 strains (A and B) of RBT. Eight fish from each of the 4 families were allotted to individual tanks. Fish were fed until satiation for 5 weeks when four fish within each family were randomly selected for 2 weeks of starvation. After the starvation period, all fish were harvested. Hepatic in-vitro LKR activity and lysine oxidation were measured as was LKR mRNA. No effect of family within strain on LKR activity or lysine oxidation was detected. Strain A exhibited a 55% reduction (p < 0.01) in LKR transcripts compared to strain B pooled across both feeding levels. Within each family, LKR mRNA was decreased (p < 0.01) in starved vs. fed fish. On average, there was a 68% decrease in LKR transcripts for starved fish. LKR activity averaged 104 ± 33 and 150 ± 31 nmol/min*gm liver (p > 0.1) in fed and starved fish, respectively. Lysine oxidation averaged 1.2 ± 0.5 and 2.2 ± 0.4 nmol/min*gm liver (p > 0.1) in fed and starved fish, respectively. LKR transcripts were positively correlated to weight gain (p < 0.01). These data are consistent with multiple modes of LKR regulation in fish.
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ABSTRACT: Although studies have established that exogenous growth hormone (GH) treatment stimulates growth in fish, its effects on target tissue gene expression are not well characterized. We assessed the effects of Posilac (Monsanto, St. Louis, MO), a recombinant bovine GH, on tissue transcript levels in rainbow trout selected from two high-growth rate and two low-growth rate families. Transcript abundance was measured in liver and muscle with the Genome Research in Atlantic Salmon Project (GRASP) 16K cDNA microarray. A selection of the genes identified as altered by the microarray and transcripts for insulin-like growth factors, growth hormone receptors (GHRs), and myostatins were measured by real-time PCR in the liver, muscle, brain, kidney, intestine, stomach, gill, and heart. In general, transcripts identified as differentially regulated in the muscle on the microarray showed similar directional changes of expression in the other nonhepatic tissues. A total of 114 and 66 transcripts were identified by microarray as differentially expressed with GH treatment across growth rate for muscle and liver, respectively. The largest proportion of these transcripts represented novel transcripts, followed by immune and metabolism-related genes. We have identified a number of genes related to lipid metabolism, supporting a modulation in lipid metabolism following GH treatment. Most notable among the growth-axis genes measured by real-time PCR were increases in GHR1 and -2 transcripts in liver and muscle. Our results indicate that short-term GH treatment activates the immune system, shifts the metabolic sectors, and modulates growth-regulating genes.
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ABSTRACT: The U.S. Department of Agriculture's National Center for Cool and Cold Water Aquaculture is conducting a breeding program for rainbow trout Oncorhynchus mykiss to develop improved germplasm for the U.S. aquaculture industry. Current selection efforts are focused on growth and disease resistance, but stress response is also a concern. Using plasma cortisol concentrations after a 3-h crowding stress as a measure of stress responsiveness, we have previously shown family variation in cortisol responsiveness and a positive phenotypic correlation between poststressor cortisol level and growth performance within our broodstock. Selection for improved growth performance may therefore increase cortisol responsiveness to stress. In the present studies, narrow-sense heritability (h2) for cortisol responsiveness was estimated to be moderately high by means of midparent–offspring regression and nested family design analyses (h2 ≥ 0.40 and 0.56, respectively). In addition, fish from the same families were used to determine associations between cortisol responsiveness to crowding and resistance to Yersinia ruckeri, the pathogenic agent of enteric redmouth disease, in an immersion challenge. Phenotypic and breeding values for cortisol responsiveness were not correlated with survivability with respect to Y. ruckeri whether or not the fish experienced repeated daily exposure to a crowding stress before the disease challenge. Furthermore, phenotypic and breeding values for poststressor plasma glucose and chloride levels and lysozyme activity did not correlate with disease survivability in stressed and unstressed fish. Finally, there was no correlation between the survival values of families when they were stressed before the disease challenge and when they were not, suggesting that there is variability among families in the effect of stress on resistance to Y. ruckeri.
