Growth Hormone Transgenic Coho Salmon Research Articles

Rationed and satiated growth hormone transgenic Coho Salmon (Oncorhynchus kisutch) show tissue specific differences in energy stores.

Growth hormone transgenic coho salmon experience increased growth rates, driven primarily through elevated feed intake and feed conversion. However, neuropeptides that signal appetite stimulation have been shown to exhibit variable responses across fed states, suggesting a more complex system mediating growth in these fish. Studies have proposed that growth hormone may have a modulatory role on the energy reserves of fish, possibly through AMP-activated protein kinase (AMPK) activation. AMPK, an energy sensor in cells, has previously been shown to be upregulated in growth hormone transgenic salmon when compared to wild type, however, whether this effect is seen across fed states is unknown. Here, we tested the hypothesis that growth hormone induces an energetic deficit in metabolic tissues, leading to constitutive AMPK activation in growth hormone transgenic salmon. This study compared AMPK activity, ATP, and glycogen, of the liver, heart, and muscle of wild-type, and growth hormone transgenic salmon either fed to satiation or a wild-type ration. The results suggest that white muscle ATP levels in growth hormone salmon are elevated in satiation and rationed conditions. In the liver, growth hormone transgenic salmon fed a rationed wild-type diet experience reductions in ATP level and glycogen. In none of the tissues examined, did AMPK activity change. Taken together, these results indicate that growth hormone transgenic salmon experience metabolic duress when not fed to satiation.

Fast-growing growth hormone transgenic coho salmon (Oncorhynchus kisutch) show a lower incidence of vaterite deposition and malformations in sagittal otoliths.

In fish otoliths, CaCO3 normally precipitates as aragonite, and more rarely as vaterite or calcite. A higher incidence of vaterite deposition in otoliths from aquaculture-reared fish has been reported and it is thought that high growth rates under farming conditions might promote its deposition. To test this hypothesis, otoliths from growth hormone (GH) transgenic coho salmon and non-transgenic fish of matching size were compared. Once morphometric parameters were normalized by animal length, we found that transgenic fish otoliths were smaller (-24%, -19%, -20% and -30% for length, width, perimeter and area, respectively; P<0.001) and rounder (-12%, +13.5%, +15% and -15.5% in circularity, form factor, roundness and ellipticity; P<0.001) than otoliths from non-transgenic fish of matching size. Interestingly, transgenic fish had smaller eyes (-30% eye diameter) and showed a strong correlation between eye and otolith size. We also found that the percentage of otoliths showing vaterite deposition was significantly smaller in transgenic fish (21-28%) than in non-transgenic fish (69%; P<0.001). Likewise, the area affected by vaterite deposition within individual otoliths was reduced in transgenic fish (21-26%) compared with non-transgenic fish (42.5%; P<0.001). Our results suggest that high growth rates per se are not sufficient to cause vaterite deposition in all cases, and that GH overexpression might have a protective role against vaterite deposition, a hypothesis that needs further investigation.

Assessing wild genetic background and parental effects on size of growth hormone transgenic coho salmon

Experiments examining potential impacts of growth hormone (GH) transgenesis in fish typically use a single source strain and do not address potential differential impacts in strains of different genetic backgrounds. Here, we examine the effects of differing genetic backgrounds when reared in culture on the growth of transgenic and nontransgenic coho salmon (Oncorhynchus kisutch) produced by mating sires from different rivers with transgenic dams from a single origin. We found a significant difference in size between offspring of sires originating from various river systems in British Columbia. This difference was independent of differences between transgenotypes (i.e., transgenic vs. nontransgenic offspring). However, the effects of strain or sire were relatively small compared to the effects of the transgene, which were consistent regardless of sire origin. Thus, results derived from studies of GH transgenic fish from a single source population can provide useful information for assessments of GH transgenic salmon from other systems. This has important implications for examining potential risks from introgression of a transgene into different populations.

Assessing the effects of genotype-by-environment interaction on epigenetic, transcriptomic, and phenotypic response in a Pacific salmon.

Genotype-by-environment (GxE) interactions are non-parallel reaction norms among individuals with different genotypes in response to different environmental conditions. GxE interactions are an extension of phenotypic plasticity and consequently studying such interactions improves our ability to predict effects of different environments on phenotype as well as the fitness of genetically distinct organisms and their capacity to interact with ecosystems. Growth hormone transgenic coho salmon grow much faster than non-transgenics when raised in tank environments, but show little difference in growth when reared in nature-like streams. We used this model system to evaluate potential mechanisms underlying this growth rate GxE interaction, performing RNA-seq to measure gene transcription and whole-genome bisulfite sequencing to measure gene methylation in liver tissue. Gene ontology (GO) term analysis revealed stress as an important biological process potentially influencing growth rate GxE interactions. While few genes with transcription differences also had methylation differences, in promoter or gene regions, many genes were differentially methylated between tank and stream environments. A GO term analysis of differentially methylated genes between tank and stream environments revealed increased methylation in the stream environment of more than 95% of the differentially methylated genes, many with biological processes unrelated to liver function. The lower nutritional condition of the stream environment may cause increased negative regulation of genes less vital for liver tissue function than when fish are reared in tanks with unlimited food availability. These data show a large effect of rearing environment both on gene expression and methylation, but it is less clear that the detected epigenetic marks are responsible for the observed altered growth and physiological responses.

Comparison of growth rates between growth hormone transgenic and selectively-bred domesticated strains of coho salmon (Oncorhynchus kisutch) assessed under different culture conditions

Aquaculture continues to be the fastest-growing animal food sector and accounts for over 50% of the world's fish consumption. This trend is projected to continue, highlighting the role that the aquaculture industry will play in ensuring future global food security. Enhancement of growth rates of fish can optimize aquaculture production and has been achieved through selective breeding programs producing fast-growing domesticated strains, or the development of growth hormone (GH) transgenic strains. Although the ability of selectively-bred domesticated and GH transgenic salmon to outgrow wild-type salmon is well documented, very little research has been reported that directly compares the growth rates of domesticated and GH transgenic strains. The aim of the present study was to compare the growth and survival of selectively-bred domesticated and GH transgenic coho salmon across a range of experimental conditions. We performed four experiments investigating the growth rates of domesticated and GH transgenic salmon by comparing these strains at different developmental stages and under different experimental rearing conditions, as well as under conditions when strains were competing and when they were reared separately. Results from all experiments showed that GH transgenic coho salmon grew faster and to a larger size than the selectively-bred domesticated coho salmon. This was true whether fish groups were reared post-smolt in freshwater or seawater, whether reared together or separately, and whether manipulated to be size-matched at early stages. Thus, GH transgenesis could become a viable complement to selective breeding to produce fast-growing salmon for aquaculture systems. While further research can continue to optimize the development and use of transgenic strains, the data presented here also are important for environmental risk assessments by providing data on the relative fitness and ecological consequences of selectively-bred domesticated and GH transgenic fish should they enter nature.

Loci associated with variation in gene expression and growth in juvenile salmon are influenced by the presence of a growth hormone transgene

BackgroundGrowth regulation is a complex process influenced by genetic and environmental factors. We examined differences between growth hormone (GH) transgenic (T) and non-transgenic (NT) coho salmon to elucidate whether the same loci were involved in controlling body size and gene expression phenotypes, and to assess whether physiological transformations occurring from GH transgenesis were under the influence of alternative pathways. The following genomic techniques were used to explore differences between size classes within and between transgenotypes (T vs. NT): RNA-Seq/Differentially Expressed Gene (DEG) analysis, quantitative PCR (qPCR) and OpenArray analysis, Genotyping-by-Sequencing, and Genome-Wide Association Study (GWAS).ResultsDEGs identified in comparisons between the large and small tails of the size distributions of T and NT salmon (NTLarge, NTSmall, TLarge and TSmall) spanned a broad range of biological processes, indicating wide-spread influence of the transgene on gene expression. Overexpression of growth hormone led to differences in regulatory loci between transgenotypes and size classes. Expression levels were significantly greater in T fish at 16 of 31 loci and in NT fish for 10 loci. Eleven genes exhibited different mRNA levels when the interaction of size and transgenotype was considered (IGF1, IGFBP1, GH, C3–4, FAS, FAD6, GLUT1, G6PASE1, GOGAT, MID1IP1). In the GWAS, 649 unique SNPs were significantly associated with at least one study trait, with most SNPs associated with one of the following traits: C3_4, ELA1, GLK, IGF1, IGFBP1, IGFII, or LEPTIN. Only 1 phenotype-associated SNP was found in common between T and NT fish, and there were no SNPs in common between transgenotypes when size was considered.ConclusionsMultiple regulatory loci affecting gene expression were shared between fast-growing and slow-growing fish within T or NT groups, but no such regulatory loci were found to be shared between NT and T groups. These data reveal how GH overexpression affects the regulatory responses of the genome resulting in differences in growth, physiological pathways, and gene expression in T fish compared with the wild type. Understanding the complexity of regulatory gene interactions to generate phenotypes has importance in multiple fields ranging from applications in selective breeding to quantifying influences on evolutionary processes.

Influence of a growth hormone transgene on the genetic architecture of growth-related traits: A comparative analysis between transgenic and wild-type coho salmon.

Genetic engineering has been increasingly applied to many commercially important plant and animal species, generating phenotypic changes that are not observed in natural populations and creating genetic interactions that have not experienced natural selection. The degree to and way in which such human‐induced genetic variation interacts with the rest of the genome is currently largely unknown. Integrating such information into ecological and risk assessment frameworks is crucial to understand the potential effects of genetically modified organisms in natural environments. Here, we performed QTL mapping to investigate the genetic architecture of growth‐related traits in nontransgenic (NT) and growth hormone transgenic (T) coho salmon with large changes in growth and related physiology, with the aim of identifying how an inserted transgene might influence the opportunity for selection. These fish shared the same parental genetic background, thus allowing us to determine whether the same or different loci influence these traits within the two groups. The use of over 1,700 loci, derived from restriction site‐associated DNA sequencing, revealed that different genomic regions were linked with growth over time between the two groups. Additionally, the effect sizes of detected QTL appear to have been influenced by the transgene. Direct comparison of QTL between the T and NT fish during two size‐matched periods identified little overlap in their location. Taken together, the results showed that the transgene altered the genetic basis of growth‐related traits in this species. The study has important implications for effective conservation and management of wild populations experiencing introduction of transgenes. Evolutionary changes and their ecological consequences may occur at different rates and in different directions in NT versus T individuals in response to selection. Thus, assessments of phenotypic change, and hence ecological risk, should be determined periodically to evaluate whether initial estimates made with founder strains remain valid.

Internal Morphological Effects of Growth Hormone Transgenesis in Coho Salmon

AbstractEffects of growth hormone (GH) overexpression on internal morphology were examined in homozygous and hemizygous GH transgenic Coho Salmon Oncorhynchus kisutch aided by clearing and staining and magnetic resonance imaging methodologies. Morphological effects of transgenesis were observed in pin bones in fast‐growing hemizygous transgenic salmon, in vertebral column and swim bladder deformities in homozygotes, and as nonproportional modifications to some cranial structures examined among groups. These data provide further examples of the complex pleiotropic effects arising from GH overexpression in transgenic salmon.

Assessing the capacity for compensatory growth in growth-hormone transgenic coho salmon Oncorhynchus kisutch.

The effect of feed cycling (consisting of periods of starvation followed by periods of refeeding to satiation) on compensatory growth was evaluated in growth hormone transgenic and non-transgenic wild-type coho salmon Oncorhynchus kisutch. The specific growth rate (GSR ) of feed-restricted non-transgenic O. kisutch was not significantly different from the GSR of fully-fed non-transgenic O. kisutch during two refeeding periods, whereas the GSR of feed-restricted transgenic O. kisutch was significantly higher in relation to the GSR of fully-fed transgenic O. kisutch during the second refeeding period, but not during the first, indicating that growth compensation mechanisms are different between non-transgenic and growth-hormone (GH)-transgenic O. kisutch and may depend on life history (i.e. previous starvation). Despite the non-significant growth rate compensation in non-transgenic O. kisutch, these fish showed a level of body mass catch-up growth not displayed by transgenic O. kisutch.

Effect of growth hormone overexpression on gastric evacuation rate in coho salmon.

Growth hormone (GH) transgenic (T) coho salmon consistently show remarkably enhanced growth associated with increased appetite and food consumption compared to non-transgenic wild-type (NT) coho salmon. To improve understanding of the mechanism by which GH overexpression mediates food intake and digestion in T fish, feed intake and gastric evacuation rate (over 7days) were measured in size-matched T and NT coho salmon. T fish displayed greatly enhanced feed intake levels (~2.5-fold), and more than 3-fold increase in gastric evacuation rates relative to NT coho salmon. Despite the differences in feed intake, no differences were noted in the time taken from first ingestion of food to stomach evacuation between genotypes. These results indicate that enhanced feed intake is coupled with an overall increased processing rate to enhance energy intake by T fish. To further investigate the molecular basis of these responses, we examined the messenger RNA (mRNA) levels of several genes in appetite- and gastric-regulation pathways (Agrp1, Bbs, Cart, Cck, Glp, Ghrelin, Grp, Leptin, Mc4r, Npy, and Pomc) by qPCR analyses in the brain (hypothalamus, preoptic area) and pituitary, and in peripheral tissues associated with digestion (liver, stomach, intestine, and adipose tissue). Significant increases in mRNA levels were found for Agrp1 in the preoptic area (POA) of the brain, and Grp and Pomc in pituitary for T coho salmon relative to NT. Mch and Npy showed significantly lower mRNA levels than NT fish in all brain tissues examined across all time-points after feeding. Mc4r and Cart for T showed significantly lower mRNA levels than NT in the POA and hypothalamus, respectively. In the case of peripheral tissues, T fish had lower mRNA levels of Glp and Leptin than NT fish in the intestine and adipose tissue, respectively. Grp, Cck, Bbs, Glp, and Leptin in stomach, adipose tissue, and/or intestine showed significant differences across the time-points after feeding, but Ghrelin showed no significant difference between T and NT fish in all tested tissues.

Salinity acclimation and advanced parr–smolt transformation in growth-hormone transgenic coho salmon (Oncorhynchus kisutch)

Growth hormone (GH) is involved in the parr–smolt transformation of salmonid fishes and is known to improve salinity tolerance. This study compared the capacity for seawater acclimation of GH transgenic coho salmon (Oncorhynchus kisutch (Walbaum, 1792)) to that of wild-type fish, allowing examination of responses to sustained (chronic) exposure to elevated GH. GH transgenic fish (GH TG) smolted 1 year in advance of wild-type salmon and showed a greater capacity to hypo-osmoregulate in seawater. As GH TG fish were much larger than the wild-type fish, a second experiment was conducted with three size-matched groups of coho salmon (a 1+-year-old wild-type group, a 1+-year-old ration-restricted GH TG group, and a 0+-year-old fully fed GH TG group). When size-matched, the effect of GH transgenesis was not as dramatic, but the feed-rationed TG1+ group exhibited smaller deviations in plasma ion and osmolality levels following seawater exposure than did the other groups, suggesting a somewhat improved hypo-osmoregulatory ability. These results support a role for GH in the development of seawater tolerance by salmonid fishes independent of fish size.

Behaviour of growth hormone transgenic coho salmon Oncorhynchus kisutch in marine mesocosms assessed by acoustic tag telemetry.

Underwater acoustic tag telemetry was used to assess behavioural differences between juvenile wild-type (i.e. non-transgenic, NT) and growth hormone (GH) transgenic (T) coho salmon Oncorhynchus kisutch in a contained simulated ocean environment. T O. kisutch were found across days to maintain higher baseline swimming speeds than NT O. kisutch and differences in response to feeding were detected between T and NT genotypes. This is the first study to assess behaviour of GH transgenic salmonids in a marine environment and has relevance for assessing whether behavioural effects of GH overexpression seen in freshwater environments can be extrapolated to oceanic phases of the life cycle.

Fitness component assessments of wild-type and growth hormone transgenic coho salmon reared in seawater mesocosms

Growth hormone (GH) transgenic fish have been proposed for use in aquaculture to enhance production efficiency. As part of a risk analysis for use of such fish, the influence of GH transgenesis on the potential to persist and succeed in natural ecosystems is being examined in confined laboratory conditions. GH transgenesis can greatly accelerate growth and, in culture conditions, is associated with secondary effects such as poor swimming capacity and spawning success. However, standard culture has also been shown to negatively affect fitness components of wild-type fish, raising the question of whether culture conditions influence fitness components of transgenic fish in a similar way. To examine factors influencing the phenotype of marine-stage GH transgenic salmon (T), and to determine if genotype-by-environment interactions exist at this life stage, we grew T and wild-type (NT) coho salmon (Oncorhynchus kisutch) over six cohort years in 350,000L seawater tanks (termed mesocosms) designed to minimize effects of standard culture conditions. Mesocosm rearing partially facilitated development of normal size and morphology of NT fish relative to nature-reared counterparts, but altered overall body shape, indicating mesocosm conditions do not fully mimic natural environmental effects on coho salmon phenotype. T fish reared in mesocosms had larger mass at maturity than mesocosm- or nature-reared NT fish, indicating GH transgenesis can alter maximum obtainable mass in salmon. Unlike NT, T fish obtained maximum size at maturity across environments, suggesting marine environmental conditions may affect T growth less than NT growth. Screening parents for a common disease agent (Renibacterium salmoninarum) improved seawater survival, and T fish had lower survival than NT fish when from unscreened parents and inconsistent relative survival when from screened parents, indicating GH transgenesis may constitute an advantage or disadvantage in terms of survival. Transgenic salmon had lower swimming capacity and aerobic scope, but similar routine metabolic rate and thermal tolerance, demonstrating transgenesis can have different influences depending on what phenotype is examined. Using an alternate strain of T fish in phenotypic comparisons did not greatly influence most fitness components, although had a strong effect on female fecundity. The inconsistent influence of GH transgenesis on different fitness components, and existence of genotype-by-environment interactions during the marine life stage, complicates extrapolation of laboratory data for transgenic fish to natural environments. However, current and previous data do not provide evidence that overall increased performance of GH transgenic salmon over wild-type fish would arise in the marine environment. Statement of relevanceRearing in seawater mesocosms demonstrate that growth hormone transgenesis has inconsistent effects on marine fitness components in coho salmon.

Regulation of feeding behavior and food intake by appetite-regulating peptides in wild-type and growth hormone-transgenic coho salmon

Survival, competition, growth and reproductive success in fishes are highly dependent on food intake, food availability and feeding behavior and are all influenced by a complex set of metabolic and neuroendocrine mechanisms. Overexpression of growth hormone (GH) in transgenic fish can result in greatly enhanced growth rates, feed conversion, feeding motivation and food intake. The objectives of this study were to compare seasonal feeding behavior of non-transgenic wild-type (NT) and GH-transgenic (T) coho salmon (Oncorhynchus kisutch), and to examine the effects of intraperitoneal injections of the appetite-regulating peptides cholecystokinin (CCK-8), bombesin (BBS), glucagon-like peptide-1 (GLP-1), and alpha-melanocyte-stimulating hormone (α-MSH) on feeding behavior. T salmon fed consistently across all seasons, whereas NT dramatically reduced their food intake in winter, indicating the seasonal regulation of appetite can be altered by overexpression of GH in T fish. Intraperitoneal injections of CCK-8 and BBS caused a significant and rapid decrease in food intake for both genotypes. Treatment with either GLP-1 or α-MSH resulted in a significant suppression of food intake for NT but had no effect in T coho salmon. The differential response of T and NT fish to α-MSH is consistent with the melanocortin-4 receptor system being a significant pathway by which GH acts to stimulate appetite. Taken together, these results suggest that chronically increased levels of GH alter feeding regulatory pathways to different extents for individual peptides, and that altered feeding behavior in transgenic coho salmon may arise, in part, from changes in sensitivity to peripheral appetite-regulating signals.

Potential risks of trophic impacts by escaped transgenic salmon in marine environments

SUMMARYThere is significant concern about potential ecological effects of introduced organisms, including non-indigenous species and those created by genetic modification. This paper presents an Ecopath with Ecosim modelling approach, designed to examine long-term trophic effects of growth hormone (GH) transgenic coho salmon should they ever escape to a coastal salmonid ecosystem, namely the Strait of Georgia in British Columbia (Canada). The model showed that the effects of introduced GH transgenic coho salmon varied with their biomass, diet, structure of the invaded ecosystem, and environmental conditions. Occasional escapes of non-reproductive salmon did not have a significant impact on the example ecosystem. However, effects of GH coho salmon varied with their diet when large numbers of these fish were present in the simulated ecosystem (for example, when they constituted 20% of total current aquaculture production in the area). Further, climate-driven changes in the biomass of low trophic levels (bottom-up effects) could have a greater impact on the ecosystem than the introduction of large numbers of GH coho salmon. A new version of Ecopath with Ecosim's Monte Carlo approach showed that the model predictions were robust to GH coho salmon's Ecopath parameters, but more sensitive to vulnerabilities of prey to GH coho salmon. Modelling ecosystem effects of genetically modified organisms provides a complementary approach for risk assessments when data from nature are not readily obtainable.

Rearing in seawater mesocosms improves the spawning performance of growth hormone transgenic and wild-type coho salmon.

Growth hormone (GH) transgenes can significantly accelerate growth rates in fish and cause associated alterations to their physiology and behaviour. Concern exists regarding potential environmental risks of GH transgenic fish, should they enter natural ecosystems. In particular, whether they can reproduce and generate viable offspring under natural conditions is poorly understood. In previous studies, GH transgenic salmon grown under contained culture conditions had lower spawning behaviour and reproductive success relative to wild-type fish reared in nature. However, wild-type salmon cultured in equal conditions also had limited reproductive success. As such, whether decreased reproductive success of GH transgenic salmon is due to the action of the transgene or to secondary effects of culture (or a combination) has not been fully ascertained. Hence, salmon were reared in large (350,000 L), semi-natural, seawater tanks (termed mesocosms) designed to minimize effects of standard laboratory culture conditions, and the reproductive success of wild-type and GH transgenic coho salmon from mesocosms were compared with that of wild-type fish from nature. Mesocosm rearing partially restored spawning behaviour and success of wild-type fish relative to culture rearing, but remained lower overall than those reared in nature. GH transgenic salmon reared in the mesocosm had similar spawning behaviour and success as wild-type fish reared in the mesocosm when in full competition and without competition, but had lower success in male-only competition experiments. There was evidence of genotype×environmental interactions on spawning success, so that spawning success of transgenic fish, should they escape to natural systems in early life, cannot be predicted with low uncertainty. Under the present conditions, we found no evidence to support enhanced mating capabilities of GH transgenic coho salmon compared to wild-type salmon. However, it is clear that GH transgenic salmon are capable of successful spawning, and can reproduce with wild-type fish from natural systems.

Glucose metabolic gene expression in growth hormone transgenic coho salmon

Salmonids are generally known to be glucose intolerant. However, previous studies have shown that growth hormone (GH) transgenic coho salmon display modified nutritional regulation of glycolysis and lipogenesis compared to non-transgenic fish, suggesting the potential for better use of glucose in GH transgenic fish. To examine this in detail, GH transgenic and non-transgenic coho salmon were subjected to glucose tolerance test and subsequent metabolic assessments. After intra-peritoneal injection of 250mg/kg glucose, we analysed post-injection kinetics of glycaemia and expression of several key target genes highly involved in glucose homeostasis in muscle and liver tissues. Our data show no significant differences in plasma glucose levels during peak hyperglycaemia (3–6h after injection), demonstrating a similar glucose tolerance between transgenic and non transgenic. However, and unrelated to the hyperglycaemic episode, GH transgenic fish return to a slightly lower basal glycaemia values 24h after injection. Correspondingly, GH transgenic fish exhibited higher mRNA levels of glucokinase (GK) and glucose-6-phosphate dehydrogenase (G6PDH) in liver, and glucose transporter (GLUT4) in muscle. These data suggest that these metabolic actors may be involved in different glucose use in GH transgenic fish, which would be expected to influence the glucose challenge response. Overall, our data demonstrate that GH transgenic coho salmon may be a pertinent animal model for further study of glucose metabolism in carnivorous fish.

Disease resistance and health parameters of growth-hormone transgenic and wild-type coho salmon, Oncorhynchus kisutch

To extend previous findings regarding fish health and disease susceptibility of growth-enhanced fish, hematological and immunological parameters have been compared between growth hormone (GH) transgenic and wild-type non-transgenic coho salmon (Oncorhynchus kisutch). Compared to non-transgenic coho salmon, transgenic fish had significantly higher hematocrit (Hct), hemoglobin (Hb), mean cellular hemoglobin (MCH), mean cellular volume (MCV), and erythrocyte numbers, and lower white cell numbers. In addition, resistance to the bacterial pathogen Aeromonas salmonicida (causal agent of furunculosis) has been assessed between the strains. Higher susceptibility of transgenic fish to this disease challenge was observed in two separate year classes of fish. The present findings provide fundamental knowledge of the disease resistance on GH enhanced transgenic coho salmon, which is of importance for assessing the fitness of transgenic strains for environmental risk assessments, and for improving our understanding effects of growth modification on basic immune functions.

Oxidative stress in growth hormone transgenic coho salmon with compressed lifespan – a model for addressing aging

Growth hormone (GH) transgenic fish have dramatically enhanced growth rates, increased oxygen demands and reactive oxygen species production. GH-transgenic coho salmon provide an opportunity to address effects of increased metabolism on physiological aging. The objective of this study was to compare oxidative stress in wild-type (WT) and GH-transgenic (T) coho salmon (Oncorhynchus kisutch) of different ages (1 and 2 years). Antioxidant enzyme activity, protein carbonyls (PC) and glutathione (GSH, GSSG) were measured. PC correlated to growth rates in individual fish. T fish exhibited lower antioxidant enzyme activities and GSH levels compared to the WT, while levels of PC and GSSG were higher. Age affects were observed in both WT and T fish; enzyme activities and GSH decreased while PC and GSSG increased. Our results support the metabolic rate theory of aging. This study aims to be a platform for continued studies of the theories of aging using fish as model organisms.

Growth of growth hormone transgenic coho salmon Oncorhynchus kisutch is influenced by construct promoter type and family line

Several different transgenic growth hormone (GH) gene constructs have been used to obtain accelerated growth in salmonids. However, there have been limited direct comparisons of these constructs in terms of the ability to achieve maximal growth in fish. We examined the effect of promoter type (sockeye salmon metallothionein-B or histone 3) fused to a growth hormone-1 coding region from the same species (OnMTGH1 and OnH3GH1 constructs respectively) on growth and plasma growth hormone (GH) and insulin-like growth factor-I (IGF-I) in multiple strains of GH transgenic coho salmon (Oncorhynchus kisutch). Salmon transgenic for the OnMTGH1 construct had consistently greater overall weight than those containing the OnH3GH1 construct, although both groups possessed greatly accelerated growth over non-transgenic fish. However, there were strong strain effects, where some OnH3GH1 strains had similar weight to OnMTGH1 strains while others did not. Triploidy diminished growth acceleration and decreased condition factors in both a fast growing MT strain and slower growing H3 strain. Plasma GH levels did not correlate to weight in transgenic strains, and all but one transgenic strain had plasma GH levels similar to equal sized non-transgenic fish. In contrast, plasma IGF-I content correlated well to size in transgenic strains. The mechanism by which accelerated growth in transgenic fish is obtained appears to be due in part to an upregulation of GH action through increased circulating IGF-I levels, and promoter-type appears to influence potential for growth.