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Doubled haploid gynogens are individuals whose genetic material consists of two identical maternal chromosome sets and who lack paternal genetic contributions. These individuals can be useful in whole‐genome sequence assembly to eliminate allelic variation in an individual that otherwise complicates the discrimination of SNPs and paralogs in regular diploids. This is particularly important in salmonid species, which have extensive remnants of an ancestral whole‐genome duplication. Further, doubled haploid individuals are fully homozygous and can be used to generate clonal lines. Here, successful timing was determined for late pressure shocking for producing doubled haploid gynogens in five Oncorhynchus species (Chinook Salmon O. tshawytscha, Coho Salmon O. kisutch, Chum Salmon O. keta, Pink Salmon O. gorbuscha, and Sockeye Salmon O. nerka) and one Salvelinus species (domesticated Artic Char Salvelinus alpinus). For this study, sperm was treated with UV irradiation to inactivate the paternal nuclear DNA and used to fertilize eggs. The resulting zygotes were pressure shocked at various times following fertilization to form doubled haploid embryos via inhibition of the first cell division (mitotic gynogenesis). At an incubation temperature of 10.5°C, successful postfertilization pressure shock times for maximal survival of confirmed gynogens were 2.41–2.83 accumulated thermal units (ATUs) for Coho Salmon, 2.63–2.84 ATUs for Chum Salmon, 2.84–3.06 ATUs for Pink Salmon, 2.19 ATUs for Sockeye Salmon, and 2.63–3.06 ATUs for Chinook Salmon, whereas for Arctic Char a shock time of 2.29–2.54 ATUs at 4°C incubation was successful. Survival to fry stage ranged from less than 1% to 11.7%. Survivors were genotyped using microsatellite markers to assess nonpaternity and maternal homozygosity and were found to be 92.5% gynogens when averaged across all treatments and species. Mitotic gynogenetic individuals were produced in all six salmonid species and were used in subsequent studies to generate whole‐genome sequences for Chinook, Coho, Chum, and Sockeye salmons. [ABSTRACT FROM AUTHOR]

Domesticated and growth hormone (GH) transgenic salmon provide an interesting model to compare effects of selected versus engineered phenotypic change on relative fitness in an ecological context. Phenotype in domestication is altered via polygenic selection of traits over multiple generations, whereas in transgenesis is altered by a single locus in one generation. These established and emerging technologies both result in elevated growth rates in culture, and are associated with similar secondary effects such as increased foraging, decreased predator avoidance, and similar endocrine and gene expression profiles. As such, there is concern regarding ecological consequences should fish that have been genetically altered escape to natural ecosystems. To determine if the type of genetic change influences fitness components associated with ecological success outside of the culture environments they were produced for, we examined growth and survival of domesticated, transgenic, and wild-type coho salmon fry under different environmental conditions. In simple conditions (i.e. culture) with unlimited food, transgenic fish had the greatest growth, while in naturalized stream tanks (limited natural food, with or without predators) domesticated fish had greatest growth and survival of the three fish groups. As such, the largest growth in culture conditions may not translate to the greatest ecological effects in natural conditions, and shifts in phenotype over multiple rather than one loci may result in greater success in a wider range of conditions. These differences may arise from very different historical opportunities of transgenic and domesticated strains to select for multiple growth pathways or counter-select against negative secondary changes arising from elevated capacity for growth, with domesticated fish potentially obtaining or retaining adaptive responses to multiple environmental conditions not yet acquired in recently generated transgenic strains. [ABSTRACT FROM AUTHOR]

There is persistent commercial interest in the use of growth modified fishes for shortening production cycles and increasing overall food production, but there is concern over the potential impact that transgenic fishes might have if ever released into nature. To explore the ecological consequences of transgenic fish, we performed two experiments in which the early growth and survival of growth-hormone transgenic rainbow trout (Oncorhynchus mykiss) were assessed in naturalized stream mesocosms that either contained predators or were predator-free. We paid special attention to the survival bottleneck that occurs during the early life-history of salmonids, and conducted experiments at two age classes (first-feeding fry and 60 days post-first-feeding) that lie on either side of the bottleneck. In the late summer, the first-feeding transgenic trout could not match the growth potential of their wild-type siblings when reared in a hydrodynamically complex and oligotrophic environment, irrespective of predation pressure. Furthermore, overall survival of transgenic fry was lower than in wild-type (transgenic = 30% without predators, 8% with predators; wild-type = 81% without predators, 31% with predators). In the experiment with 60-day old fry, we explored the effects of the transgene in different genetic backgrounds (wild versus domesticated). We found no difference in overwinter survival but significantly higher growth by transgenic trout, irrespective of genetic background. We conclude that the high mortality of GH-transgenic trout during first-feeding reflects an inability to sustain the basic metabolic requirements necessary for life in complex, stream environments. However, when older, GH-transgenic fish display a competitive advantage over wild-type fry, and show greater growth and equal survival as wild-type. These results demonstrate how developmental age and time of year can influence the response of genotypes to environmental conditions. We therefore urge caution when extrapolating the results of GH-transgenesis risk assessment studies across multiple life-history or developmental stages. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The first genetically modified ( GM) fish intended for human consumption has recently stimulated significant scientific discussion and regulatory scrutiny regarding food safety and environmental risks. Currently, no experiments with transgenic fish have been performed in nature, yet such data are needed to facilitate predictions of ecological consequences should engineered fish escape to the natural environment., To address this limitation, we conducted experiments under natural conditions but within a contained environment to assess the impact of invasion of growth-enhanced GM coho salmon Oncorhynchus kisutch ( Walbaum) on survival and growth of three naturally cohabitating fishes: Chinook salmon O. tshawytscha ( Walbaum), steelhead trout O. mykiss ( Walbaum) and conspecific wild-type coho salmon., We found that the impact of stream-reared GM coho salmon on invaded specimens was similar to the impact of non- GM coho salmon. However, GM fish significantly reduced survival and growth of the invaded populations if they were first allowed to grow larger under hatchery conditions before being released., Synthesis and applications. Our results show that the ecological impact of fish genetically modified ( GM) for rapid growth on closely related fish species may not be high in stream environments, unless these fish are first reared under culture conditions where they are able to realize their genetic growth potential. As such, first generation escapes of GM fish into the natural environment should be a main concern in the short term, whereas later generations, which are more similar to naturally occurring genotypes, are expected to have significantly weaker effects but which could persist for longer periods. [ABSTRACT FROM AUTHOR]

We tested the fitness consequences of introgression of fast-growing domesticated fish into a wild population. Fry from wild and domesticated rainbow trout ( Oncorhynchus mykiss) crosses, F1 hybrids, and first- and second-generation backcrosses were released into two natural lakes. Parentage analysis using microsatellite loci facilitated the identification of survivors, so fitness was estimated in nature from the first-feeding stage. Results indicated that under certain conditions, domesticated fish survived at least as well as wild fish within the same environment. Relative growth and survival of the crosses, however, were highly dependent on environment. During the first summer, fastest-growing crosses had the highest survival, but this trend was reversed after one winter and another summer. Although the F1 hybrids showed evidence of outbreeding depression because of the disruption of local adaptation, there was little evidence of outbreeding depression in the backcrosses, and the second-generation backcrosses exhibited a wild-type phenotype. This information is relevant for assessing the multigenerational risk of escaped or released domesticated fish should they successfully interbreed with wild populations and provides information on how to minimize detrimental impacts of a conservation breeding and/or management programme. These data also further understanding of the selection pressures in nature that maintain submaximal rates of growth. [ABSTRACT FROM AUTHOR]

Salmonids show a high degree of phenotypic plasticity that can differ among genotypes, and this variation is one of the major factors contributing to uncertainty in extrapolating laboratory-based risk assessment data to nature. Many studies have examined the relative growth and survival of transgenic and non-transgenic salmonids, and the results have been highly variable due to genotype × environment interactions. The relative survival of fast- and slow-growing strains can reverse depending on the environment, but it is not clear which specific environmental characteristics are driving these responses. To address this question, two experiments were designed where environmental conditions were varied to investigate the contribution of rearing density, food amount, food type, habitat complexity, and risk of predation on relative growth and survival of fast-growing transgenic and slow-growing wild-type coho salmon. The first experiment altered density (high vs. low) and food amount (high vs. low). Density impacted the relative growth of the genotypes, where transgenic fish grew more than non-transgenic fish in low density streams, regardless of food level. Density also affected survival, with high density causing increased mortality for both genotypes, but the mortality of transgenic relative to non-transgenic fish was lower within the high-density streams, regardless of food level. The second experiment altered habitat complexity (simple vs. complex), food type (artificial vs. natural), amount of food (normal vs. satiation), and risk of predation (present vs. absent). Results from this experiment showed that genotype affected growth and survival, but genotype effects were modulated by one or more environmental factors. The effect of genotype on survival was influenced by all examined environmental factors, such that no predictable trend in relative survival of transgenic versus non-transgenic fry emerged. This was primarily due to variations in survival of non-transgenic fish under different environmental conditions (non-transgenic fry had highest survival in hatchery conditions, and lowest survival in complex conditions with natural food fed at a normal level with or without predators). Transgenic fry survival was only significantly influenced by predator presence. The effects of genotype on mass and length were significantly modulated by food type only. Transgenic fry were able to gain a large size advantage over non-transgenic fish when fed artificial food under all habitat types. These experiments support the observations of dynamic responses in growth and survival depending on the environment, and demonstrate the challenge of applying laboratory-based experiments to risk assessment in nature. [ABSTRACT FROM AUTHOR]

Prior to the development of any conservation strategies to mitigate deleterious impacts of environmental change and contamination, there must be a method to make meaningful predictions of the effect of environmental change on organisms. Assessment of relative transcriptomic expression patterns can provide a link between the environment and the physiological response of the organism by identifying genes that respond to environmental stressors; this information could also assist in teasing apart the molecular basis of toxicological effects vs. physiological adaptation. Molecular responses to environmental stressors are probably not restricted to single or few genes, and therefore a more integrative approach is required to examine broad-scale patterns of transcriptomic response. To address this objective, used machine learning tools to link the mechanisms of physiological response to environmental stress; although widely used in clinical applications, such as finding the genetic basis of diseases (), ecological genomics applications of artificial neural networks are just beginning to emerge. Analyses such as these are important to help identify limitations on the adaptive capacity of organisms and to predict impacts of climate change, ocean acidification and anthropogenic contaminants on aquatic organisms. [ABSTRACT FROM AUTHOR]