Effect of Growth Horomone on Rainbow Trout: An Ecological Assessment of the Potential Impact of Genetic Engineering on Organism Design

Abstract

Trout genetically engineered to possess extra functioning growth homone genes were simulated, using injections of fish and bovine growth hormone. This was done to test potential and ecological impact of such genetic engineering on trout. Through analysis of growth and dry-mass budgets, it was determined that elevated levels of growth hormone resulted in increased growth and consumption. Potential constraints pertaining to respiration, density and evolutionary history were considered. Surprisingly, bovine growth hormone appeared to act as a super-normal stimuli, being more potent than the natural trout hormone. In fact the natural hormone inhibited growth at high dosages. Juvenile growth rates were less sensitive to elevated levels of growth hormone than those in more mature fish. Thus, improved growth was achieved by altering its normal ontogeny. This suggests that duplicating copies of growth hormone gene in an organism is not equivalent to a speciation event. Evidently, other manipulations would be required to increase the intrinsic metabolic power. Growth rate apparently is used as a cue for determining a particular ontogenetic trajectory (Stearns and Crandall, 1984). The fact that various species conform to one of at least four plastic developmental trajectories that are shaped by natural constraints and mortality patterns, means that growth hormone may elicit different responses in different species. The findings and implications of this study underscore the importance of using the holistic scope of ecology to achieve effective and efficient genetic engineering of target species.