Growth Hormone Transgenic Fish Research Articles

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.

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.

Genotype-environment interactions for survival and growth rate at varying levels of sodium chloride for growth hormone transgenic channel catfish (Ictalurus punctatus), channel catfish, and albino channel catfish

Lack of freshwater is emerging as the most critical natural resource issue facing humanity. Ongoing climate change will reduce freshwater supplies, and demand for food continues to expand rapidly. Swim-up channel catfish, Ictalurus punctatus, fry transgenic for the channel catfish growth hormone (GH) gene driven by the rainbow trout Oncorhynchus mykiss metallothionein promoter (rtMT-ccGH), or by the ocean pout Zoarces americanus antifreeze protein promoter (opAFP-ccGH), channel catfish, and albino channel catfish were grown at 0, 2.5, 5, and 7.5 parts per thousand (ppt) salinity. Survival was 100% for all genetic groups at 0 and 2.5 ppt. Increasing salinity to 5 ppt decreased overall survival as survival rates of rtMT-ccGH transgenic (T), rtMT-ccGH control (C), opAFP-ccGH transgenic (T), opAFP-ccGH control (C), channel catfish, and albino channel catfish were 83, 82, 83, 77, 89 and 40%, respectively. Increasing salinity to 7.5 ppt had a strong negative impact on survival as means for rtMT-ccGH (T), rtMT-ccGH (C), opAFP-ccGH (T), opAFP-ccGH (C), channel catfish, and albino channel catfish were 67, 13, 67, 10, 18, and 7%, respectively with the albino channel catfish having the lowest survival followed by opAFP-ccGH (C) (P = .002). Raising salinity to 2.5 ppt greatly increased the growth rate of GH transgenic channel catfish (11–33%), channel catfish (56%), and albino channel catfish (124%). NaCl had a negative effect on survival and growth rate for swim-up fry at 5 ppt. Significant differences were observed at varying salinity (P < .0001) for final body weights among genetic groups. Condition factor, growth and survival were not perfectly correlated, and genotype-environment interactions occurred for the overall phenotype. Apparently, GH can play a critical positive role for channel catfish under osmotic stress, which has relevance for aquaculture management under future global climate change. Optimum performance for all genotypes was observed with slightly elevated, 2.5 ppt. Although, GH transgenic catfish were less affected than non-transgenic channel catfish at 5–7.5 ppt, their performance was sub-optimal. GH transgenic fish are beneficial for use in culture environments that have slight shifts in salinity in the future, but they are only a partial solution for future environments at 5 ppt and higher.

Effect of growth rate on transcriptomic responses to immune stimulation in wild-type, domesticated, and GH-transgenic coho salmon

BackgroundTranscriptomic responses to immune stimulation were investigated in coho salmon (Oncorhynchus kisutch) with distinct growth phenotypes. Wild-type fish were contrasted to strains with accelerated growth arising either from selective breeding (i.e. domestication) or genetic modification. Such distinct routes to accelerated growth may have unique implications for relationships and/or trade-offs between growth and immune function.ResultsRNA-Seq was performed on liver and head kidney in four ‘growth response groups’ injected with polyinosinic-polycytidylic acid (Poly I:C; viral mimic), peptidoglycan (PGN; bacterial mimic) or PBS (control). These groups were: 1) ‘W’: wild-type, 2) ‘TF’: growth hormone (GH) transgenic salmon with ~ 3-fold higher growth-rate than W, 3) ‘TR’: GH transgenic fish ration restricted to possess a growth-rate equal to W, and 4) ‘D’: domesticated non-transgenic fish showing growth-rate intermediate to W and TF. D and TF showed a higher similarity in transcriptomic response compared to W and TR. Several immune genes showed constitutive expression differences among growth response groups, including perforin 1 and C-C motif chemokine 19-like. Among the affected immune pathways, most were up-regulated by Poly I:C and PGN. In response to PGN, the c-type lectin receptor signalling pathway responded uniquely in TF and TR. In response to stimulation with both immune mimics, TR responded more strongly than other groups. Further, group-specific pathway responses to PGN stimulation included NOD-like receptor signalling in W and platelet activation in TR. TF consistently showed the most attenuated immune response relative to W, and more DEGs were apparent in TR than TF and D relative to W, suggesting that a non-satiating ration coupled with elevated circulating GH levels may cause TR to possess enhanced immune capabilities. Alternatively, TF and D salmon are prevented from acquiring the same level of immune response as TR due to direction of energy to high overall somatic growth. Further study of the effects of ration restriction in growth-modified fishes is warranted.ConclusionsThese findings improve our understanding of the pleiotropic effects of growth modification on the immunological responses of fish, revealing unique immune pathway responses depending on the mechanism of growth acceleration and nutritional availability.

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.

Growth-Enhanced Transgenic Coho Salmon (Oncorhynchus kisutch) Strains Have Varied Success in Simulated Streams: Implications for Risk Assessment.

Growth hormone (GH) transgenic fish have accelerated growth and could improve production efficiency in aquaculture. However, concern exists regarding potential environmental risks of GH transgenic fish should they escape rearing facilities. While environmental effects have been examined in some GH transgenic models, there is a lack of information on whether effects differ among different constructs or strains of transgenic fish. We compared growth and survival of wild-type coho salmon (Oncorhynchus kisutch) fry, a fast-growing GH transgenic strain containing a metallothionein promoter (TMT), and three lines/strains containing a reportedly weaker histone-3 promoter (TH3) in hatchery conditions and semi-natural stream tanks with varying levels of natural food and predators. Rank order of genotype size and survival differed with varying environmental conditions, both within and among experiments. Despite accelerated growth in hatchery conditions, TMT fry gained little or no growth enhancement in stream conditions, had enhanced survival when food was limiting, and inconsistent survival under other conditions. Rank growth was inconsistent in TH3 strains, with one strain having highest, and two strains having the lowest growth in stream conditions, although all TH3 strains had consistently poor survival. These studies demonstrate the importance of determining risk estimates for each unique transgenic model independent of other models.

Fatty acid content in muscles of amago salmon homozygous or heterozygous for a growth hormone transgene

Abstract Fatty acids are a vital energy source in fish and are of significant importance to their physiological wellbeing. Amago salmon ( Oncorhynchus masou ishikawae ) transgenic for a growth hormone (GH) show both accelerated growth and altered fatty acid composition and content in liver tissues. In particular, they show a decrease in saturated fatty acids and monounsaturated fatty acids, and an increase in polyunsaturated fatty acids except for docosahexaenoic acid (22:6n− 3) and eicosapentaenoic acid (20:5n − 3). Furthermore, transgenic fish have decreased levels of serum glucose, triacylglycerol and an increase in 3-hydroxybutyric acid, generally considered a starvation marker. As liver tissue is physiologically connected to muscle tissue, here we examined the effects of GH transgenesis on fatty acid contents in muscles of homozygous and heterozygous GH transgenic fish. The major monounsaturated fatty acids oleic acid (18:1n − 9) and palmitoleic acid (16:1n − 7) were slightly higher in the control, whereas polyunsaturated fatty acids, except 22:6n − 3 and 20:5n − 3, were significantly greater in the transgenic fish ( P P

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.

Effects of domestication and growth hormone transgenesis on mRNA profiles in rainbow trout (Oncorhynchus mykiss)1

Growth rate can be genetically modified in many vertebrates by domestication and selection and more recently by transgenesis overexpressing growth factor genes [e.g., growth hormone (GH)]. Although the phenotypic end consequence is similar, it is currently not clear whether the same modifications to physiological pathways are occurring in both genetic processes or to what extent they may interact when combined. To investigate these questions, microarray analysis has been used to assess levels of mRNA in liver of wild-type and growth-modified strains of rainbow trout (Oncorhynchus mykiss). This species has been used as a model because nondomesticated wild strains are available as comparators to assess genetic and physiological changes that have arisen both from domestication and from GH transgenesis. The analysis examined pure wild-type and pure domesticated strains as well as 2 different GH transgenes (with markedly different growth effects) both in pure wild and in wild × domesticated hybrid backgrounds. Liver mRNA showed highly concordant changes (Pearson correlations; r>0.828; P<0.001) in levels in domesticated and GH transgenic fish, relative to wild-type, for both up- and downregulated genes. Furthermore, among domesticated, transgenic, and their hybrid genotypes, a strong correlation (P<0.001) was found between growth rate and the number of genes affected (r=0.761 for downregulated mRNA and r=0.942 for upregulated mRNA) or between growth rate and mRNA levels relative to wild-type (r=0.931 for downregulated mRNA and r=0.928 for upregulated mRNA). One GH transgenic strain was found to affect growth and mRNA levels similar to domestication whereas effects of the other GH transgenic strain were much stronger. For both GH transgenes, a hybrid domesticated×wild background influenced growth rate and mRNA levels to only a small extent relative to the transgenes in a pure wild-type genetic background. Functional analysis found that genes involved in immune function, carbohydrate metabolism, detoxification, transcription regulation, growth regulation, and lipid metabolism were affected in common by domestication and GH transgenesis. The common responses of mRNAs in domesticated and GH transgenic strains is consistent with the GH pathway or its downstream effects being upregulated in domesticated animals during their modification from wild-type growth rates.

Growth and endocrine effects of recombinant bovine growth hormone treatment in non-transgenic and growth hormone transgenic coho salmon

To examine the relative growth, endocrine, and gene expression effects of growth hormone (GH) transgenesis vs. GH protein treatment, wild-type non-transgenic and GH transgenic coho salmon were treated with a sustained-release formulation of recombinant bovine GH (bGH; Posilac™). Fish size, specific growth rate (SGR), and condition factor (CF) were monitored for 14weeks, after which endocrine parameters were measured. Transgenic fish had much higher growth, SGR and CF than non-transgenic fish, and bGH injection significantly increased weight and SGR in non-transgenic but not transgenic fish. Plasma salmon GH concentrations decreased with bGH treatment in non-transgenic but not in transgenic fish where levels were similar to controls. Higher GH mRNA levels were detected in transgenic muscle and liver but no differences were observed in GH receptor (GHR) mRNA levels. In non-transgenic pituitary, GH and GHR mRNA levels per mg pituitary decreased with bGH dose to levels seen in transgenic salmon. Plasma IGF-I was elevated with bGH dose only in non-transgenic fish, while transgenic fish maintained an elevated level of IGF-I with or without bGH treatment. A similar trend was seen for liver IGF-I mRNA levels. Thus, bGH treatment increased fish growth and influenced feedback on endocrine parameters in non-transgenic but not in transgenic fish. A lack of further growth stimulation of GH transgenic fish suggests that these fish are experiencing maximal growth stimulation via GH pathways.

Integration mechanisms of transgenes and population fitness of GH transgenic fish

It has been more than 20 years since the first batch of transgenic fish was produced. Five stable germ-line transmitted growth hormone (GH) transgenic fish lines have been generated. This paper reviews the mechanisms of integration and gene targeting of the transgene, as well as the viability, reproduction and transgenic approaches for the reproductive containment of GH-transgenic fish. Further, we propose that it should be necessary to do the following studies, in particularly, of the breeding of transgenic fish: to assess the fitness of transgenic fish in an aqueous environment with a large space and a complex structure; and to develop a controllable on-off strategy of reproduction in transgenic fish.

The growth promoting activity of two different kinds of recon-structed terminators in transgenic common carp

The transgenic promoter directly affects the activity of transgenic gene. Choice of terminator has been proved to affect the activity of transgenic gene. Since the relevant theoretical research is rare, using the terminator of transgenic gene or the promoter gene to construct the transgenic vector has not come to the conclusion. In order to construct a better transgenic vector to nurture "all fish" growth hormone transgenic fish which has a rapid growth character, two different transgenic vectors were constructed separately by the terminator of beta-actin gene and the terminator of growth hormone gene. After micro-injection, we obtained the P0 generation of "all fish" transgenic fish farming groups. Comparing the activities of the two different transgenic vectors, the weight distribution of the breeding groups from growth hormone gene terminator transgenic vector felt into a normal distribution; however, the weight distribution of the breeding groups originated from beta-actin gene terminator exhibited a non-normal mode and in a rightist trend. The average weight of GH (Growth hormone) gene terminator transgenic groups was significantly higher than that of the beta-actin gene terminator transgenic groups. Interestingly, a fast-growth transgenic carp was found from a mixed farming group, which was positive for the growth hormone gene terminator. This result showed that "all fish" GH gene transgenic carp could grow fast, and the transgenic gene could inherit from generation to generation. Our results suggest that the growth hormone gene terminator transgenic vector has stronger growth-promoting activity than the beta-actin gene terminator transgenic vector.

Metabolism traits of ‘all-fish’ growth hormone transgenic common carp ( Cyprinus carpio L.)

Transgenic animals with improved qualities have the potential to upset the ecological balance of a natural environment. We investigated metabolic rates of ‘all-fish’ growth hormone (GH) transgenic common carp under routine conditions and during starvation periods to determine whether energy stores in transgenic fish would deplete faster than controls during natural periods of starvation. Before the oxygen uptake was measured, the mean daily feed intake of transgenic carp was 2.12 times greater than control fish during 4 days of feeding. The average oxygen uptake of GH transgenic fish was 1.32 times greater than control fish within 96 h of starvation, but was not significantly different from controls between 96 and 144 h of starvation. At the same time, GH transgenic fish did not deplete energy reserves at a faster rate than did the controls, as the carcass energy contents of the two groups following a 60-d starvation period were not significantly different. Consequently, we suggest that increased routine oxygen uptake in GH transgenic common carp over that of control fish may be mainly due to the effects of feeding, and not to an increase in basal metabolism. GH transgenic fish are similar to controls in the regulation of metabolism to normally distribute energy reserves during starvation.

Progress in the evaluation of transgenic fish for possible ecological risk and its containment strategies

Genetically improved transgenic fish possess many beneficial economic traits; however, the commercial aquaculture of transgenic fish has not been performed till date. One of the major reasons for this is the possible ecological risk associated with the escape or release of the transgenic fish. Using a growth hormone transgenic fish with rapid growth characteristics as a subject, this paper analyzes the following: the essence of the potential ecological risks posed by transgenic fish; ecological risk in the current situation due to transgenic fish via one-factor phenotypic and fitness analysis, and mathematical model deduction. Then, it expounds new ideas and the latest findings using an artificially simulated ecosystem for the evaluation of the ecological risks posed by transgenic fish. Further, the study comments on the strategies and principles of controlling these ecological risks by using a triploid approach. Based on these results, we propose that ecological risk evaluation and prevention strategies are indispensable important components and should be accompanied with breeding research in order to provide enlightments for transgenic fish breeding, evaluation of the ecological risks posed by transgenic fish, and development of containment strategies against the risks.

Changes in hepatic gene expression related to innate immunity, growth and iron metabolism in GH-transgenic amago salmon ( Oncorhynchus masou) by cDNA subtraction and microarray analysis, and serum lysozyme activity

Growth hormone (GH) transgenic amago salmon ( Oncorhynchus masou) were generated with a construct containing the sockeye salmon GH1 gene fused to the metallothionein-B (MT-B) promoter from the same species. This transgene directed significant growth enhancement with transgenic fish reaching approximately four to five times greater weight than control salmon in F 2 and F 3 generations. This drastic growth enhancement by GH transgene is well known in fish species compared with mammals, however, such fish can show morphological abnormalities and physiological disorders like other GH transgenic animals. GH is known to have many acute effects, but currently there are no data describing the chronic effects of over-expression of GH on various hepatic genes in GH transgenic fish. Hepatic gene expression is anticipated to play very important roles in many physiological functions and growth performance of transgenic and control salmon. To examine these effects, we performed subtractive hybridization (using cDNA generated from liver RNA) in both directions to identify genes both increased and decreased in transgenic salmon relative to controls (576 clones were isolated and sequenced in total). Heme oxygenase, vitelline envelope protein, Acyl-coA binding protein, NADH dehydrogenase, mannose binding lectin-associated serine protease, hemopexin-like protein, leucyte-derived chemotaxin2 (LECT2), and many other genes were obtained in higher clone frequencies suggesting enhanced expression. In contrast, complement C3-1, lectin, rabin, alcohol dehydrogenase, Tc1-like transposase, Δ6-desaturase, and pentraxin genes were obtained in lower frequencies. Microarray analysis was also performed to obtain quantitative expression data for these subtracted cDNA clones. Analysis of fish across seasons was also conducted using both F 2 and F 3 salmon. Results of the microarray data essentially corresponded with those of the subtraction data when both F 2 and F 3 fish were completely immature, but the expression pattern was changed when fish approached maturation. Genes showing enhanced expression in GH transgenic fish in F 2 and F 3 by array analysis were vitelline envelope protein, hemopexin-like protein, heme-oxygenase, inter α-trypsin inhibitor, LECT2, GTP cyclohydrolase I feedback regulatory protein (GFRP), and bikunin. Reduced expression genes were lectin, Δ6-desaturase, apolipoprotein, and pentraxin. In particular, lectin was found to be highly suppressed in all F 2 and immature F 3 salmon. Further, serum lysozyme activity, one of innate immunity, was significantly ( p < 0.05) decreased in both F 2 and F 3 GH transgenic fish. These results indicate that the GH transgene fish had altered hepatic gene expression relating to iron-metabolism, innate immunity, reproduction, and growth.

Growth, viability and genetic characteristics of GH transgenic coho salmon strains

Transgenic coho salmon strains containing an all-salmon growth hormone (GH) gene construct (OnMTGH1) have been examined. The transgene utilized is comprised of the metallothionein-B promoter driving the expression of the type-I growth hormone gene from sockeye salmon. Transgene DNA is integrated into the salmon genome, but is transmitted at low frequency from founder transgenic animals consistent with late integration following microinjection resulting in mosaic animals, whereas subsequent generations transmit transgene DNA as a stable Mendelian trait. Different families established from separate founder animals yield lines with unique growth characteristics suggesting important site-of-integration effects on transgene expression. Growth enhancement of transgenic salmon is initiated early, with advanced hatch timing but occurring also throughout the life history, particularly during the early phase in fresh water. GH transgenic fish showed precocious smoltification and onset of sexual maturation, but approximately normal adult body size, indicating that compression of the normal coho salmon life history is occurring. The viability of diploid GH transgenic salmon ranges from reductions to greater than that of controls among strains, and triploid transgenic animals had normal viability relative to diploid transgenic salmon. Triploid transgenic salmon display a reduction in growth rate relative to transgenic diploids, but are still significantly growth enhanced compared with nontransgenic controls. The distinct phenotypic characteristics of GH transgenic families suggest that evaluation for aquaculture and for risk assessments requires examination of strains on a case-by-case basis. Furthermore, strong effects of size at maturity in culture conditions were observed for nontransgenic wild strain coho salmon which were not apparent in GH transgenic salmon, indicating that strong genotype by environment effects strongly influence phenotype and complicate risk assessments.

Effects of growth hormone transgenesis on metabolic rate, exercise performance and hypoxia tolerance in tilapia hybrids

Swimming respirometry was employed to compare inactive metabolic rate (Rr), maximum metabolic rate (Rmax), resultant aerobic scope and maximum sustainable (critical) swimming speed (Ucrit), in growth hormone transgenic (GHT) and wild‐type (W) tilapia Oreochromis sp. hybrids. Although the Rr of GHT tilapia was significantly (58%) higher than their W conspecifics, there were no significant differences in their net aerobic scope because GHT tilapia exhibited a compensatory increase in Rmax that was equal to their net increase in Rr. As a consequence, the two groups had the same Ucrit. The GHT and W tilapia also exhibited the same capacity to regulate oxygen uptake during progressive hypoxia, despite the fact that the GHT fish were defending a higher demand for O2. The results indicate that ectopic expression of GH raises metabolic rate in tilapia, but the fish compensate for this metabolic load and preserve such physiological determinants of fitness as aerobic scope, swimming performance and tolerance of hypoxia.

Increased ability to compete for food by growth hormone-transgenic coho salmonOncorhynchus kisutch(Walbaum)

In salmonids, growth hormone (GH) stimulates growth, appetite and the ability to compete for food. This study tested the hypothesis that increased GH levels in GH-transgenic coho salmon Oncorhynchus kisutch (Walbaum) increase competitive ability through higher feeding motivation. The transgenic strain of salmon used contained a gene construct consisting of the sockeye metallothionein-B promoter fused to the type 1 growth gene coding region. The transgenic animals (mean size = 250 g) were F1 individuals. In six consecutive feeding trials, the intake of contested food pellets by size-matched pairs consisting of one control (1 year older non-transgenic coho salmon) and one GH-transgenic coho salmon was compared. Pellets were provided sequentially until neither fish took three consecutive pellets; the identity of the fish taking each pellet was noted. Calculated on the three first pellets offered at each feeding trial, the transgenic coho salmon consumed 2.5 times more contested pellets than the controls, supporting the hypothesis that GH transgenesis increases the ability to compete for food. Overall, the transgenic fish consumed 2.9 times more pellets that the non-transgenic controls, indicating a high feeding motivation of the transgenic fish throughout the feeding trials. It appears that GH transgenesis and GH treatments can induce similar changes in the feeding behaviour of salmonids. Depending on how transgenic and wild individuals differ in other fitness-related characters, escaped GH transgenic fish may compete successfully with native fish in the wild.

Growth hormone increases predation exposure of rainbow trout

The energetic state of an animal strongly influences decisions that balances feeding against predation risk. Growth hormone increases the metabolic demands, which should elevate the feeding motivation of an animal. This, in turn, may increase the willingness to risk exposure to predators during feeding. To test this hypothesis, we studied the effect of growth hormone on the behavioural response of rainbow trout (Oncorhynchus mykiss) to simulated attacks from a model heron. After attacks, growth hormone treated trout foraged closer to the water surface, resumed feeding earlier, and ate more food than did control trout. Such behaviour should increase the susceptibility to aerial predation. Thus, predation may select against high endogenous growth hormone secretion in wild fish. Furthermore, genetic manipulations to increase growth hormone levels, intended to improve growth performance in aquaculture, may result in individuals with substantially altered behavioural patterns. In light of the increasing potential for interactions between farmed and wild fish, growth hormone transgenic fish may pose a threat to wild fish populations.