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002727 considcrable consequence. predation on e9gs or young by inl(Oduccd fishes has nol been demonstraled (0 be a common occurcncc (Taylor cl at 1984). Spatiol AlterOfion Concommittant overlap in usage of space by non-native and native fishes may leap to c.ompclititve intecaction if space is in limited su.p'ply 01' 01 variable quality. Evidence exists implicating displacement of brook trout by brown (rout, but in general, displacernenls are largely inferential (faylor el aI. 1984). Con. versely, high densities of introduced fIShes have been shown to exert negative effects on nalive fIShes. For example. Noble et al. (1975) observed that largemouth bass populations in Trinidad Lake, Texas. declined with no evidence of recruitment as densi. ties or blue tilapia rose to approximalely 2,240 kg/ha. during the period or 1972-,975. Gene Pool Delef'i-.Jration Through reduction of heterogeneity through inbreeding is clearly a threat to any species being produced in a hatchery (Philipp et aI. 1983), Ihe risk is most acule with species of intercontinental origin because the initial broodstock invariably represent limited gene pools at the outset. The larger the stock. ing program. the more inbreeding among original broodstock is necessary. Thus species introduced to a novel habitat mayor may not have the genet~c cha.ra.cteristics necessary {or them to adapt and/or penofTT' as predicted. Fortunately. hybriuization eve.nts among introduced and native species in open waters are rare (Taylor et a1. 1984). NevertheJess, (h~ possibility of native gene: pools being 3ltered through such hybridization does exist. For example, broum trout are knov.,." to hybridize W;th native forms in North Amer- ;ca (Schwartz 1972. 1981; Dangel et al. 1973; Chevassos 1979). In~oduc!ion of Diseoses Di!>eJ.ses caused by bacteria, viruses, and pa:asites are all too oh~n conveyed along with introduced aquatic species (see Hoffman and Schubel 1984; Shotts and Gratzek 1984 for rev~eUJs). This aspect represents one of the most severe threats th~t an introduced species may pose to a native community. Transfer of diseased fish was no doubt responsible. {or introduc. tion of whirling disease into North America from Europe. Recently, i.nlectious hypodermal and hematopoietic necrosis virus (lHHNV) has been spread to a number of countries in conjunction with shipments of live penaeid shrimp. IHHNV was first diagnosed in 1981 at shrimp culture facilities in Hawaii among shrimp introduced from Panama (Sindermann 1986). Even "ich," one of the most common fish diseases world\.vide, caused by a ciliated protozoan, is thought to have ~en trans- ferred from Asia throughout -the: 'temperate zone with ship' ments of fishes fHoffman 1970, 1981). C. Courses of Action Introduction of species 10 aquatic communities are com. monly employed as a fisheries management (001 or occor as a r~sult of escapes from aquaculture or om3mental f\Sh haWing facilities. It is not feasible. nOf desirable. 10 legislate against all such inlroouclions_ Whal is needed is more education on the role that introduced species can and should play in the context of ~Qualic resources management. The more informed natural resource' managers MC aboul such issues. the less likely that Table 1. Organisms cited in (exl. Common Name Scientific Name Pion's hydriJia water hyacinth Eurasian watermilfoil alligator weed FISh Pacific salmon grass carp common carp tilapias J-Iydril/a ucrticil/ata Eichornio crassipes Myriophyllum spicatum Allemonrhera phiJoxeroides Oncorhyncus sp. Clenophoryngodon ideHo CWrinus carpio o..eochromis. Sorotherodon and Tilopio sp. Oreochromis aureus (= T,/opio oureouJ Ti1opio ziIli $almo trolla Belonesox belizanus Astronotus ocel1olus Boirdielh i:istio Soluelinus Jontino&s Mcropterus solmoides Oncorhyncus kisulch Marone saxatUis Cionas batrochus blue lilapia redbelly lilapia brown trout pike killifISh oscar bairdiella brook trout largemouth bass coho S2J.mon striped bass walking catfish Other whirling disease "ich" My:rosoma cerebralis Ichrhyopthiriu5 multijiIiis misiakes will be m~de or that legislation will be necessary 10 ~nforce an ".)ttil~dp. of caution." The f"lbwing z.clions toward that end are recommended. A. The membership realfirms its endorsement of the 1972 .. "Position of the American Fisheries 5ocle~y on lntroouctiof, oi Exotic Aquatic SpeciC'S.' as modified: Position of Ame.rica.n Fi.sheries Sociely on Introduced Aqua:ic Species_ .Our purpose is to formulate ~ broad mechanism for planning, regulating, implementing, and monitoring all introductions of aquatic species. Some introductions or species into ecosystems in which they are not native have been successful and others unfortunate. Species not native to an ccos>'ste:m will be lermed "intra. duced:' Some introductions erc in some sense, planned Clnd purpose.{ul (or management reasons: others Me acc\denta\ m 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 hobbyisls 10 prevent and discourage the <1ccidental or purposeful intro- duction of aquatic species into their local ecosystems. 2_ Urge that no city, coumy. state, province, or fcdf>.ral agency-introduce, or a.\\ow to be. introduced, an)' spec.i.es. 'I"Ito.- any waters within its junsdiction which (T\lght contaminate an~' waters outside its jurisdiction without otrK:ial sanclion of Ihe ex.posed jurisdiction. 3. Urge Ihat only ornamcnl.)! '"'Cluarium fish de31c(!> be per. mitted to import such ftshes (or :...)Ie or dIstribution to houb...isl s. '-23'