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ally introduced. Current programs to assess introductions were often set up to limit the possi- bility that pathogens or parasites would be intro- duced with species to be stocked. The Great Lakes Fishery Commission requires notification of salmonid introductions and has set up a proto- col to prevent introductions of salmonid diseases (Hnath 1993, Horner and Eshenroder 1993), and the Atlantic States Marine Fisheries Commission (ASMFC) has set up a procedural plan to deal with interjurisdictiona] transfers and introductions of shellfish to prevent the spread of disease (ASMFC 1989). As noted, any effort to reduce the risks associated with the introduction of an organism would have to include an assess- ment of its pathogens and other cryptic or asso- ciated flora or fauna. Introductions of nonindigenous strains may have deleterious genetic impacts on indigenous species. Because the qualities selected for in stocking or aquaculture programs may not nec- essarily be those that enhance survival in the wild, large scale releases or escapes of these strains may compromise the survivability of the indigenous species. Interbreeding of indigenous species with hatchery products or introduced strains may reduce adaptations that arc geneti- cally linked and thus result in a loss of natural genetic diversity. Such introductions may also lead to outbreeding depression (Waples 1991). Although the record is limited, there is increasing concern that open system aquaculture and stock- ingprograms may have deleterious impacts on wild stocks of the same species. More attention has been given to salmonids in this respect than to other species. There is increasing evidence that localized population units are adapted to specific environmental conditions. Such charac- teristics as timing and extent of migrations, size and shape at various life stages, optimal water temperatures, behavioral differences, and resis- tance to specific diseases may be genetically linked (Taylor 1991, Ferguson 1990). Although noting the limited information base, Hindar et al. (1991) concluded, "...any substantial influx of exogenous genes, may it be gene flow or com- plete displacement, has a negative effect on per- formance. In some instances, severe population reductions have followed introductions of cul- tured fish." Concern has been raised that large- scale escapes from open aquaculture facilities and stocking programs may threaten local wild stocks resulting in the loss of genetic adaptations (Gausen and Moen 1991, Waples, 1991). Two scientists have developed population models demonstrating that even if there is limited repro- duction of nonindigenous stocks, introductions of large numbers of cultured fish may lead to extinctions of wild stocks (Hutchings 1991, Evans and Willox 1991), Introductions of nonindigenous species also may affect indigenous species by altering habitat. The aquatic plant hydrilla (Hydrilla verticillata) was apparently released and spread both intentionally via aquarium dumping and unintentionally via transport on boat trailers. Hydrilla can clog water bodies and threaten both biotic resources and recreational activities (Courtenay and Williams 1992). Schardt and Schmitz (]990) reported that of Florida's nonindigenous aquatic plants "most were deliberately transplanted." For example, Australian melaleuca (Melaleuca quin- quenervia) was imported to Florida for forestry purposes but has since extensively invaded the State's wetlands (Culotta 1991, Schmitz et al. 1991). At one point, melaleuca seeds were even scattered by airplane. Interestingly, a similar sug- gestion has recently been made for the aerial dis- persal of "millions of killifish eggs" for mosquito control purposes (Kaczor 1992). Between the U.S. Army Corps of Engineers and the Tennessee Valley Authority, the Federal govern- ment spent $l3 million on research and control of aquatic plants in Fiscal Year 1992. Aquatic plants are a particularly important com- ponent of aquatic ecosystems because they make up the key interfaces between sediment, the water column and the atmosphere controlling both productivity and biogeochemical cycles as well as structuring aquatic habitats (Carpenter and Lodge 1986). Both fish and invertebrates tend to be more abundant and diverse in macro- phyte beds than in adjacent open water (Wiley et al. 1984, Killgore et al, 1989). Benthic popula- tions under macrophyte beds can exceed 100 times that which occurs in open areas (Miller et al. 1989). The introduction of macrophytes that become aquatic nuisance species tends to alter aquatic habitat. When introduced, such species often experience a rapid phase of dispersal and growth. Where indigenous plant species occur, the intro- duced species often have a competitive advantage due to a lack of natural predators or some mor- phological or physiological attribute. Hydrilla can withstand lower light and dissolved oxygen levels than most competing indigenous rooted aquatic 9