decreasing the amount of feed needed to bring a fish to market size, while reducing wastes per unit of mass produced. Production of fish expressing a phytase transgene might allow use of less fish meal in feeds while decreasing phosphorus in effluent from aquaculture operations. However, transgenic fish and shellfish might pose environmental hazards (Kapuscinski and Hallerman, 1990; 1991; Hallerman and Kapuscinski, 1992a,b; 1993; Muir and Howard, 1999; 2001; 2002a,b). Below, the committee briefly reviews a series of empirical studies to examine potential ecologic risks posed by escaped or released transgenic fish and shellfish.
As indicated in Table 5.1, there are a number of important factors that contribute to risk. The risk factors for establishment in a community were high for all categories because: (1) cultured fish and shellfish stocks are not far removed from the wild type, (2) aquaculture production systems frequently are located in ecosystems containing wild or feral populations of conspecifics, (3) aquatic organisms exhibit great dispersal ability, and (4) aquacultured organisms often are marketed live.
Transgenic Atlantic salmon pose a near-term regulatory issue. A brief review of the hazards they pose provides a useful illustration of the environmental hazards posed by GE aquatic species more generally. Cultivated salmon escape from fish farms in large numbers (Carr et al., 1997; Youngson et al., 1997; Fisk and Lund, 1999; Volpe et al., 2000), posing ecologic and genetic risks to native salmon stocks (Hansen et al., 1991; Hindar et al., 1991). Several studies that have focused on Atlantic salmon (Salmo salar) expressing a growth hormone (GH) gene construct suggest that transgenesis might affect fitness, but do not provide net fitness estimations needed for parameterizing fitness models predicting outcomes should such fish enter natural systems. GH transgenic salmon consumed food and oxygen at more rapid rates than control salmon (Stevens et al., 1998); although gill surface area was 1.24 times that in control salmon, it did not compensate for the 1.6-time elevation in oxygen uptake, and the metabolic cost of swimming was 1.4 times that for control salmon (Stevens and Sutterlin, 1999). Growth-enhanced transgenic fish were significantly more willing to risk exposure to a predator in order to gain access to food (Abrahams and Sutterlin, 1999), but reduced their exposure to predators when risk was heightened further, suggesting that they might not be significantly more susceptible to predation. Transgenic salmon lost their juvenile parr markings sooner than nontransgenics, suggesting early readiness for adaptation to seawater. Thus, findings to date are fragmentary, and it is difficult to assess the likely ecologic or genetic outcome should transgenic Atlantic salmon escape captivity and invade wild populations.
Pacific salmonids include a number of aquaculturally important species that have been the subject of a large number of transgenesis experiments and a small number of risk assessment experiments. These studies collectively show results similar to those obtained with Atlantic salmon, but also show that the