Monster Seminar Jam - Effect of GH Transgenesis
Dr. Robert Devlin, Aquaculture Division, Department of Fisheries and Oceans Canada
Fish with enhanced growth have been developed using selective breeding or transgenic approaches to study basic growth physiology and for potential use in aquaculture. The commercial application of these technologies has been scientifically and socially controversial, primarily due to potential environmental impacts which may arise from escape of these strains into nature. Risk assessment information is required to determine whether the genetic, physiological and behavioural characteristics of such animals is altered relative to wild strains, with consequent effects on survival and reproductive fitness. For coho salmon and rainbow trout, introgression of growth-enhanced domesticated genotypes into wild strains over three generations has revealed that phenotypic differences are primarily due to additive genetic effects and are diluted with each backcross generation. In contrast, phenotypes have been stable over six generations for transgenic strains overexpressing growth hormone (GH). Growth of transgenic strains can be dramatically enhanced, initiating early in development and resulting in precocious hatching, smoltification, and sexual maturity, suggesting an overall compression of the salmon life history is occurring. Regulation of normal GH gene expression has been disrupted in transgenic animals, and constitutive overexpression of GH leads to increased IGF-I gene transcription and circulating hormone levels in some strains. Non-allometric growth is observed for some organs and tissues, resulting in developmental abnormalities (acromegaly) and altered organ structure. Physiological performance can also be affected, including impaired swimming ability, metabolic efficiency, and disease resistance, and enhanced digestive efficiency. Some characteristics of transgenic fish may confer both enhancement and impairment of fitness, complicating fitness assessments. For example, transgenic fish have highly enhanced appetites and feeding behaviour which results in increased ability to compete for available food resources, but this same trait also results in increased predation mortality in semi-natural habitats. Similarly, for reproductive fitness, spawning success of transgenic coho salmon in laboratory arenas is impaired relative to wild salmon, but female fecundity is enhanced. Thus, while these fitness traits can be identified as important forces differentiating transgenic and wild fish, their exact magnitude cannot yet be reliably estimated from laboratory facilities due to significant genotype x environment interactions. These uncertainties in risk assessments for transgenic organisms in nature suggest that the development of completely reliable reproductive containment strategies is highly warranted to prevent interaction between wild and genetically-distinct fish.
Date and Time:
March 3, 2005,
11:00 am - 12:30 pm