WSP04306

• File Number: 8240.200.10.H
• Description: UCRBRIP Stocking
• Basin: Colorado Mainstem
• Date: 9/5/1996
• Author: UCRBRIP
• Title: Procedures for Stocking Nonnative Fish Species in the Upper Colorado River Basin
• Water Supply Pro - Doc Type: Publication

considerable consequence. predation on eggs or young by
introduced fishes has nol been demonslraled to be a common
occurcoce (Taylor et al. 1984).

Spatial Alteration

Concommittant overlap in usage of space by non.native and
native fishes may lea.d 10 compelilicve inleraction if space is in
limited sup-ply or of variable quality. Evidence exists implicating
displacement of brook trout by brown trout, but in general,
displacements are largely inferential (Taylor et aI. 1984). Con.
versely, h;gh densities of introduced raShes have been shown to
exert negative effects on native raShes. Forexample. Noble et a!.
(1975) obsOlVed that largemouth bass populationS in Trinidad
Lake, Texas, declined with no evidenceo( recruitment as densi-
ties of blue tilapia rose to approximately 2,240 kg/ha" during the
period of 1972.J975.

Gene Pool DetenJrOlion

Through reduction of heterogeneity through inbreeding is
clearly a threat to any species being produeed in a hatchery
(Philipp et aI. 1983), the risk is most acute with species of
intercontinental origin because the initial broodstockinvariably
represent limited gene pools at theoutsel. Thelargerthe stock.
ing program, the more inbreeding among original broodstock is
necessazy. Thus species introdueed to a novel habitat mayor
may not have the genetic characteristics necessary (or them to
adapt and/or pedonT' as predicted.
Fortunately. hybriuization events among introdueed and
native species in open waters are rare (Taylor et aJ. 1984).
Nevertheless. the possibility of native gene pools being altered
through sueh hybridization does exist. For example, brown
trout arc known to hybridize with native forms in North Amer-
ica (Schwartz 1972. 1981; Dangel et a!. 1973: Chevassus (979).

Introduction of Diseases

Diseases caused by bacteria, viruses, and pa:asites areall too
often conveyed along with introduced aquatic species (see
Hoffman and Schubert 1984; ShOlls and Gratzek 1984 for
reviews). This aspect represents onf:of the most severe threats
that an introduced spedes may pose to a native community.
Transfer of diseased fish was no doubt responsible fo( introdue.
tion of whirling disease into North America from Europe.
Recently, infectious hypodermal and hematopoietic necrosis
virus (IHHNV) has been spread to a number o( countries in
conjunction with shipments of live pe:naeid shrimp.1HHNV wa's
first diagnosed in 1981 at shrimp cullure-facililies in Hawaii
among shrimp introduced from Panama (Sindermann 1986).
Even "ich," one of the most commOn fish diseases worldwide,
caused by a ciliated pro1ozoan, is thoughlto have been-trans.
ferred from Asia throughout ,the -temperate zone with ship.
menls of fishes (Hoffman 1970. 1981).

C. Courses or Action

lotroduClion of species 10 aqualic communities arc com.
monly employed as a fisheries managemenl (001 or occur as a
result of escapes from aquaculture or ornamental nsh 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 in thecontcxt
of i,qualic resourceS managemenl. The more infonned natural
resource. managers Me about such issues. the less likely thaI

Table l. Organisms citcd in led.

Common Name

Scientific Name

Plants
hydrilia
walel hyacin( h
Eurasian watermilloil
aUigator weed
FISh .
Pacific salmon
grass carp
common carp
tilapias

J-/ydrilla ucrricillota
Eichoroio crossipes
MyriophJA1um spicolum
A/temonthera ph/Joxeroides

Oncorhyncus sp.
Ctenophoryngodon ideOa
Cwrinus corpio
Oreochromis, Sorotherodon
and 1iI0pio .p.
Oreochromis oureus
(= 1iI0pia oureou)
Tilapiozi11i
Sa/mo lrulla
Belanesox belizanus
Astronotus ocellatus
Boircflel1a idstia
Sa/ue1inus fontinatis
MicropteJUS salmaides
Oncorhyncus kisulch
Marone saxatilis
Clarias botrochus

blue lilapia

redbeUy tilapia
b(()wn trout
pike killifISh
oscar
bairdieUa
brook troUt
Iargemouth bass
coho salmon
striped bass
walking catfish
Other
whirling disease
4<kh"

Myxosoma cerebralis
lchlhyoplhirius multi)iliis

mistakes will be mace or that legislation will be necessary Co
enforce an "i1tlilude of caution." The following actions toward
that end are recommended.

A. The membership reaffirms ;lS endorsement of the 1972
." "Position of the American Fisheries Society on Introduction of
Exotic Aquatic Species" as modified:
Position of American Fisheries Society on
Introduced AQ~atic Species.
.Our purpose is to formulate i! broad mechanism for planning.
regulating. implementing, and monitoring all introductions of
aquatic species.
Some introductions of species inlo ecosystems in \vhich they
are not native have been successful and others unfortunate.
Species not native to an ccos\.'stem will be termed "intro'
duced." Some introductions ~re in some sense. planned and
purposeful for management reasons; others arc accidental or
are simply ways of disposing 01 unwanted pelS or research
organisms.
- -It is recommended that the policy of the American Fisheries
Society be:
1. Encourage fish impartels, farmers, dealers. and hobbyists
10 prevent and discourage the ~ccidcnlal or pUlposeful intro.
duction of aquatic species inlo Iheir local ecosysten-c..
2. Urge that nc;> city. county. state. province, or led....ral
agency-introduce, or allow to be introduced. any species into.
any waters within its jurisdictK,n which (night contaminale an~1
waters outside its jurisdiction wilhout offICial sanction of the
exposed jurisdiction.
3. Urge that only ornamenl,)I"\QuJriunl 'ish dealers be per.
mined to import such fjshes for :~)leordistribuliollIO hobb~JisIS.

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