Migration and growth potential of coho salmon smolts: implications for ecological impacts from growth-enhanced fish

Importance of Experimental Environmental Conditions in Estimating Risks and Associated Uncertainty of Transgenic Fish Prior to Entry into Nature

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.

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.

Alternate Directed Anthropogenic Shifts in Genotype Result in Different Ecological Outcomes in Coho Salmon Oncorhynchus kisutch Fry

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.

Gene--environment interactions influence feeding and anti-predator behavior in wild and transgenic coho salmon

Environmental conditions are known to affect phenotypic development in many organisms, making the characteristics of an animal reared under one set of conditions not always representative of animals reared under a different set of conditions. Previous results show that such plasticity can also affect the phenotypes and ecological interactions of different genotypes, including animals anthropogenically generated by genetic modification. To understand how plastic development can affect behavior in animals of different genotypes, we examined the feeding and risk-taking behavior in growth-enhanced transgenic coho salmon (with two- to threefold enhanced daily growth rates compared to wild type) under a range of conditions. When compared to wild-type siblings, we found clear effects of the rearing environment on feeding and risk-taking in transgenic animals and noted that in some cases, this environmental effect was stronger than the effects of the genetic modification. Generally, transgenic fish, regardless of rearing conditions, behaved similar to wild-type fish reared under natural-like conditions. Instead, the more unusual phenotype was associated with wild-type fish reared under hatchery conditions, which possessed an extreme risk averse phenotype compared to the same strain reared in naturalized conditions. Thus, the relative performance of genotypes from one environment (e.g., laboratory) may not always accurately reflect ecological interactions as would occur in a different environment (e.g., nature). Further, when assessing risks of genetically modified organisms, it is important to understand how the environment affects phenotypic development, which in turn may variably influence consequences to ecosystem components across different conditions found in the complexity of nature.

Accuracy of nonmolecular identification of growth-hormone- transgenic coho salmon after simulated escape

Concerns with transgenic animals include the potential ecological risks associated with release or escape to the natural environment, and a critical requirement for assessment of ecological effects is the ability to distinguish transgenic animals from wild type. Here, we explore geometric morphometrics (GeoM) and human expertise to distinguish growth-hormone-transgenic coho salmon (Oncorhynchus kisutch) specimens from wild type. First, we simulated an escape of 3-month-old hatchery-reared wild-type and transgenic fish to an artificial stream, and recaptured them at the time of seaward migration at an age of 13 months. Second, we reared fish in the stream from first-feeding fry until an age of 13 months, thereby simulating fish arising from a successful spawn in the wild of an escaped hatchery-reared transgenic fish. All fish were then assessed from 'photographs by visual identification (VID) by local staff and by GeoM based on 13 morphological landmarks. A leave-one-out discriminant analysis of GeoM data had on average 86% (72-100% for individual groups) accuracy in assigning the correct genotypes, whereas the human experts were correct, on average, in only 49% of cases (range of 18-100% for individual fish groups). However, serious errors (i.e., classifying transgenic specimens as wild type) occurred for 7% (GeoM) and 67% (VID) of transgenic fish, and all of these incorrect assignments arose with fish reared in the stream from the first-feeding stage. The results show that we presently lack the skills of visually distinguishing transgenic coho salmon from wild type with a high level of accuracy, but that further development-of GeoM methods could be useful in identifying second-generation,fish from nature as a nonmolecular approach.

Ecological risk analysis and genetically modified salmon: management in the face of uncertainty

The commercialization of growth hormone transgenic Atlantic salmon for aquaculture has become a controversial public policy issue. Concerns exist over the potential ecological effects of this biotechnology should animals escape captivity. From within an ecological risk-analysis framework, science has been sought to provide decision makers with evidence upon which to base regulatory decisions pertaining to genetically modified salmon. Here I review the available empirical information on the potential ecological and genetic effects of transgenic salmon and discuss the underlying eco-evolutionary science behind the topic. I conclude that data gaps and irreducible epistemic uncertainties limit the role of scientific inference in support of ecological risk management for transgenic salmon. I argue that predictive uncertainties are pervasive in complex eco-evolutionary systems and that it behooves those involved in the risk-analysis process to accept and communicate these limitations in the interest of timely, clear, and cautious risk-management options.

Inside the heads of David and Goliath: environmental effects on brain morphology among wild and growth-enhanced coho salmon Oncorhynchus kisutch

Transgenic and wild-type individual coho salmon Oncorhynchus kisutch were reared in hatchery and near-natural stream conditions and their brain and structure sizes were determined. Animals reared in the hatchery grew larger and developed larger brains, both absolutely and when controlling for body size. In both environments, transgenics developed relatively smaller brains than wild types. Further, the volume of the optic tectum of both genotypes was larger in the hatchery animals and the cerebellum of transgenics was smaller when reared in near-natural streams. Finally, wild types developed a markedly smaller telencephalon under hatchery conditions. It is concluded that, apart from the environment, genetic factors that modulate somatic growth rate also have a strong influence on brain size and structure.

Black carp growth hormone gene transgenic allotetraploid hybrids of Carassius auratus red var. (♀)×Cyprinus carpio (♂)

Ecological safety is a major consideration in the commercialization of transgenic fish. Development of sterile transgenic triploid fish through hybridization of transgenic tetraploid fish and transgenic diploid fish is a feasible way to solve this problem. The "all-fish" transgene, pbcAbcGHc, containing the black carp β-actin gene promoter and the open reading frame (ORF) of the black carp growth hormone (GH) gene was constructed and introduced into fertilized eggs of allotetraploid fish through microinjection. Contrast cultivation results showed that the growth rate of 150 day-old P(0) black carp GH gene transgenic allotetraploid fish was much higher than that of controls. Sixty 150 day-old transgenic allotetraploid fish were assayed by PCR for transgene integration and 90% of fish were positive for the transgene. The transgene was detected in 13 of 20 sperm samples from male transgenic allotetraploid fish. RT-PCR detected transcription of the exogenous black carp GH gene in the muscle, liver, kidney and ovaries of the largest transgenic allotetraploid fish. This study has developed P(0) black carp GH gene transgenic allotetraploid fish with a highly increased growth rate, which provides a solid foundation for the establishment of a pure line of transgenic allotetraploid fish and for the large scale production of sterile transgenic triploid fish.

[Progress in transgenic fish techniques and application]

Transgenic technique provides a new way for fish breeding. Stable lines of growth hormone gene transfer carps, salmon and tilapia, as well as fluorescence protein gene transfer zebra fish and white cloud mountain minnow have been produced. The fast growth characteristic of GH gene transgenic fish will be of great importance to promote aquaculture production and economic efficiency. This paper summarized the progress in transgenic fish research and ecological assessments. Microinjection is still the most common used method, but often resulted in multi-site and multi-copies integration. Co-injection of transposon or meganuclease will greatly improve the efficiency of gene transfer and integration. "All fish" gene or "auto gene" should be considered to produce transgenic fish in order to eliminate misgiving on food safety and to benefit expression of the transferred gene. Environmental risk is the biggest obstacle for transgenic fish to be commercially applied. Data indicates that transgenic fish have inferior fitness compared with the traditional domestic fish. However, be-cause of the genotype-by-environment effects, it is difficult to extrapolate simple phenotypes to the complex ecological interactions that occur in nature based on the ecological consequences of the transgenic fish determined in the laboratory. It is critical to establish highly naturalized environments for acquiring reliable data that can be used to evaluate the environ-mental risk. Efficacious physical and biological containment strategies remain to be crucial approaches to ensure the safe application of transgenic fish technology.