Environment and aquaculture in developing countries

neighboringwest coast sea-lochs but after
the farm had ceased operation the
differences were no longer apparent.
There is anecdotal evidence from
Norway (K. Tangen, pers. comm.) of an
increase in phytoplankton production as a
result of fish farming activity. Persson
(1991) suggests that there is clear evidence
of eutrophication resulting from fish
farming in coastal waters of Finland. In
the latter case, however, the measured
increase in phytoplankton biomass may
have been the result of accumulation due
to the ponding of near surface inshore
water, rather than an increase in growth
stimulated by fish farm waste (T. Miikinen,
pers. comm.). Gowen and Ezzi (1992) were
unable to measure any changes in
phytoplankton production or biomass in
relation to the nutrient enrichment they
observed and this raises an important
point: anthropogenic nutrients, including
fish farm waste, will only stimulate
phytoplankton growth ifgrowth is limited
by the availability of nutrients. In those
coastal regions where phytoplankton
growth is limited by light or the
accumulation of biomass is restricted by
dilution, eutrophication is unlikely.

Use of Chemicals in Intensive Cage

Culture

Various therapeutants are used in
intensive cage culture to control disease
and other chemicals are used to control
external parasites such as sen lice.
Concerns over the use of these chemicals
relates to their ecotoxicology, the potential
for bioaccumulation and in the case of
antimicrobialcompounds, the development
of disease resistance in target and
nontarget bacteria.
The problems experienced with the
antifouling compound tributyl tin, (used
on cage nets) serves as a good example of
why full evaluation and strict control is

necessary before a compound is licensed

for use in fish farming. Tributyl tin (now

banned for use in aquaculture in most

European countries) has been shown to be

toxic to nontarget organisms (Stepaenson

et al. 1986); accumulate in the flesh of the

farmed fish and cause mortality of farmed

fish (Short and Thrower 1986); and

accumulate through the food chain

(Laughlin 1986).

Current concerns center on the use of

dichlorvos (Nuvan or Aquaguard) an

organophosphorus compound use against

parasitic copepods (sea lice). This

compound is a general pesticide and

therefore is nonspecific, being toxic to a

range of crustacean larvae. Extensive use

of this compound in intensive cage culture

appears to have resulted in the

development of resistance in sea lice

populations andwhere repeated treatment

of fish has been carried out, increased the

sensitivity of fish to the compound. These

two factors have reduced the efficacy of

the treatment.

Interaction with Wildlife

In addition to the ecological effects of

the waste released from fish farms, the

physical presence of fish farms, the

presence of high biomasses of fish and

human activity can interact with wildlife

in a number of ways.

There have been a number of

accusations that fish farm development

has had a negative impact on wildlife, in

particular predatory birds and mammals

(Anon. 1988; Whilde 1990). While there is

clear evidence that many predatory birds

(such as cormorants, herons and shags)

and mammals (for example, seals) are

killed at fish farms (either as a result of

becoming trapped in netting or deliberately

killed), no objective studies into the effects

of these mortalities on breeding

populations have been carried out.