1982;EIFAC1988; Pursiainen 1988; EIFAC
1990), depend on site selection and engi-
neering design of aquaculture installa-
tions; selection of appropriate species and
breeds; intensity of culture systems; qual-
ity of farm management and husbandry
(diseaseprecautions, stress avoidance, feed
formulation, feeding strategies and water
quality); disposal and treatment effluents;
uses of waters affected by farm effluents;
and the sensitivity ofthese recipient waters
to farm effluents.
The freshwater environment can be
affected by the release from fish farms of
uneaten food; feces and dissolved excre-
tory products; high microbial loads, para-
sites, disease organisms and vectors; and
aquaculture chemicals, such as
anesthetics, disinfectants, biocides, food
additives, drugs for disease prophylaxis'
treatment and inorganic and organic fer-
tilizers. The chemistry of the recipient
waterbodies and their bottom sediments
can be changed by an increase in sus-
pended solids, by biochemical and chemi-
cal oxygen demands, and by increased
nutrient loading, particularly nitrogen and
phosphorus. Thus, quantitative and quali-
tative changes in the biota (bacteria,
protozoa, plankton, benthos and fish) of
recipient waterbodies are very likely.
Nutrient and organic enrichment may lead
to local eutrophication and hypoxia or
anoxia (see also Beveridge 19841, although
the fertilization of some oligotrophic waters
may increase fish production. Wild fish
populations may be threatened by dis-
eases and parasites emanating from high
levels of infection in aquaculture instal-
lations. Aquaculture chemicals and their
residues may cause sublethal and lethal
effects on wild aquatic organisms, depend-
ing on their potential for bioaccumulation,
their toxicity and characteristics of
physicochemical persistence. The self-
purification capacity of recipient waters
may be diminished by antibiotics that
inhibit microbial growth. Also, the exces-
sive use of drugs may generate drug-re-
sistant pathogens.
Such impacts on rivers and freshwa-
terlakes also depend on the residence time
and amount of water flowing through the
aquaculture installations and on the ki-
netics of the recipient waters. Here, for
instance, seasonal changes in river flow,
lake flushingand water space around cages
may well influence the dilution and dis-
tribution of contaminated waters.
Inland fisheries can be affected by
intensive freshwater aquaculture. Abstrac-
tion of water, diversion of watercourses,
dam and pond construction, and setting
up of fishpens and cages in openwater
areas, can have serious implications for
aquatic wild life. The feedingand breeding
habitats of many species could be dis-
turbed. With aquatic life cycles being
disrupted and recruitment reduced, over-
all productivity may be lowered (Dunn
1989).
Fish species with good characteristics
for farming and stocking and good mar-
ketability have been and will continue to
be introduced to new habitats. However,
introduced exotic species and genetically
modified breedsmay alter and impoverish
local aquatic biodiversity and genetic
resources, as they may affect endemic
speciesvia cornpetition,predation, destruc-
tion of habitats, transmission of parasites
and diseases, and interspecific breeding
(Welcomme 1988).
Related concerns and recommenda-
tions on the conservation and utilization
of aquatic genetic resources have been
formulated atvarious expert consultations
dealingwithgeneticresources offish, stock
enhancement and aquaculture genetics
(FAOLJNEPl98l; EIFAC 1982; Chevassus
and Coche 1986). Joint efforts by working
parties on stock enhancement and intro-
ductions of the European Inland Fisheries
Advisory Commission of FA0 (EIFAC) and
the working group on introductions and
transfers of marine organisms of the