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considerable consequence, predation on eggs or young by introduced fishes has not been demonstrated to be a common occurcncc (Taylor et al. 1984). Spotiol A6crodon Concommittant overlap in usage of space by non-native and native fishes may lead to competititve interaction i( space is in limited supplyor of variable qualify. Evidence exists implicating displacement of brook trout by brown trout, but in general, displacements are largely inferential (Taylor et al. 1984). Con- versely,high densities of introduced fishes have been shown to exert negative effects on native fishes. For example, Noble et al. (1975) observed chat largemouth bass populations in Trinidad lake, Texas, declined with no evidence of recruitment as densi- ties ofblue tilapiarose to approximately 2,240 kg/ha' during the period of ]972-:975. Gene Pool Deer: iration Through reduction of heterogeneity through inbreeding is dearly a threat to any species being produced in a hatchery (Philipp et al- 1983), the risk is most acute with species of intercontinenta]Origin because the initial broodstock invariably represent limited gene pools ai the outset. The larger the stock- ing program, the more inbreeding among original broodstock is necessary. Thus species introduced to a novel habitat may or may not have the genetic characteristics necessary for them to adapt and/or periorrr as predicted- Fortunately, hybriuization events among introduced and native species in open waters are rare (Taylor et aJ. 1984)- N2verthe]ess, the possibility of native gene pools being altered threLgh such hybridization does exist- For exar-,ply, brown Trout arc known to hybridize urth native forms in North Amer- ica (Schwartz 1972. 1981; rJangel et al. 193; Chevass~s 1979). Table I. Organisms cited in tcxt- Common NamC Sc~cntiGc Namc Plonts )tydrilia JiydnNo venic;lloro water hyacinth E~Chprni0 crossitks Eurasian walermilfoil Mynophyllum Spicotum alligator weed Altemonrhero philoxeroides Fish Pacific salmon Oncorhyncus sp. grass carp Ctenopharyngodon idelle common carp Cyprinus carpio tlapias Oreochromis, Sorotherodon and 7-Jopia sp. blue llapia Oreochromis oureus (= Tiiapio oureau) redbelly tilapia TiJapia zt71i brown trout Sclmo trutta pike killifish Belonesoz beGzonus Oscar Astronotus ocel)olus bairdiella BoirdieDa icistio brook trout Soluelinus /onfinaFis largeJnouth bass I~ficropterus soLnoides coho salmon Oncorhyncus lasutch striped bass Morone soxohTis walking catfish Clangs botrochus Other whirling disease Myxosomo cerebrolis "ich" lchthyopthinus muJti~iliu misiakes will be made or that Icg~slation will be necessary to enforce an "attitude o! caution-" The Ielhwing actions toward that end are recommended. 1 1 1 1 Jnt-oducfion o/ Gsseases Ciseases caused by bactzria, viruses, and pa: ashes are all too often conveyed along with introduced aquatic species (see Hoff;nan and Schubert 1984; Shotts grid Gratzek 1964 for reviews)-This aspect re?resents one o(;he most severe threats tiat an introduced species may pose to a native community. Transfer of diseased fish was no doubt responsible for introduc- tion of whirling disease into North America from Europe. Recently, infectious hypodermal and hematopoietic necrosis virus (1HHNV) has been spread to a number of countries in conjunction with shipments of Iwo penaeid shrimp-1HHNV was first diagnosed in 1981 at shrimp culture facilities in Hawaii among shrimp introduced from Panama (Sindermann !986). Even "ich," one of the most common fish diseases urorld~vide, caused by a ciliated protozoan, is thought to have bt;en trans- ferred from Asia throughout the temperate zone with ship menu of fishes (Hoffman 1970, 1981). C. Courses of Action Mtroduction of species ro aquatic communities arc com- monly employed as a fisheries management tool or occur as a result of escapes from aquaculture or ornamental fish holding facilities- It is not feasible, nor desirable, to legislate against all such introductions- What is needed is more education on the role that introduced species can and should play m the context of .aquatic rCSOUrCCS managcmcm. The more informed natural rC>PUrCC man,lgC~S ArC dhnut ;uch i;SUC'• IhC ICSS GkCly Thal A. The membership reaffirms its endorsement of the 1972 "Position cf the American Fisheries Society on Introduction, of Exotic Aquatic Species" as modi5ed: Position o(Ameriean Fisheries Society on Introduced Aqua;ic Species. Our purpose is to formulate ~ broad mechanism for plann~nq. regulating, implementing, and monitoring all introductions of aquatic species- Some introductionsof species into ecosystems rn which they are not native have been successful and others unfortunate. Species not natb.,e to an ecosystem will be termed "intro duced." Some introductions a:c in some sense, planned and purposeful for management reasons: others arc accidental or are simply ways of disposing of unwanted pets or research organisms. It is recommended that the policy of the American Fisheries Society be: 1- Encourage fish importers, farmers, dealers, and hobbyists to prevent and discourage the accidental or purposeful intro- duction of aquatic species into their local ecosystems. 2. Urge that no city, county, state, province, or (ed•~ral agency introduce, or allow to be introduced, any species into any waters within its jurisdiction which might contaminate any waters outside its jurisdiction without official sanUiori of the exposed jurisdiction- 3 Urgc that only ornamcnl ~I ,~quanum I~sh dCJICfS be trcr :Wined to import such [,shcs fOr `-:+IC n~ r1~51 nbut~pn to hobb•nits 22 1 t