aims of farmers, and invites genetic
manipulation to develop better breeds.
The latter uses seed similar to wildtypes
to enhance fisheries. For both, the main-
tenance of good performance requires
thorough knowledge of the characteristics
of the original populations and of .khe
changes induced by human intervention
(choice of broodstock, techniques used for
captive breeding and larval rearing, and
genetic changes due to stock management,
e.g., inbreeding). Without this knowledge
there could be reduced performance due
to genetic deterioration from the original
populations. Moreover, the availability of
the original populations of selected and
manipulated lines is vital to permit the
recovery of genes lost by intentional or
unintentional manipulations.
The objective of aquaculture is to farm
fish for food and income and to keep su.ch
farming options open for future genera-
tions. A good understanding of genetic
variation within farmed aquatic
populations is a basic prerequisite for
efficient long-term management.
The application of genetics to
aquaculture and realization of the need
for conservation of aquatic genetic re-
sources (which are largely
nondomesticated) are very recent (Ryman
1991). Maintenance of intraspecific ge-
netic variability has been long neglected
in the management of natural populations.
Indeed, farmed aquatic species were for-
merly considered to be more or less geneti-
cally homogeneous, with a large amount
of variation caused by environmental
factors. The existence of high levels of
inter- and intrapopulation genetic varia-
tion in fish was not widely recognized until
the 1960s, with the introduction of bio-
chemical analyses in population genetics
(mainly electrophoresis of enzymes) which
led to the detection of previously unrec-
ognized genetic variation. These tech-
niques are now used very widely (e.g.,
Feryson and Thorpe 1991; Utter 1991;
Whitmore 1991). It is very important to
investigate the consequences of breeding
practices on the genetic structure cnd
performance of cultured stocks. Macaranas
and Fujio (1990) have suggested investi-
gations on genetic variability and differ-
ences at loci controllingbiochemical traits,
genetic differences at loci controlling
performance traits and the correlation
between these.
Parallel to the development of
aquaculture has emerged the need to
preserve natural living aquatic resources
(inter- and intrapopulation variation) and
to establish conservation programs at local,
national, regional and international lev-
els. The widespread transfers of aquatic
species and the enormous impact of hu-
man interventions on aquatic genetic
resources (from increasing fishing efforts
and intensification of aquaculture prac-
tices) are now becoming widely discussed
in relation to conservation (Hindar et al.
1991). However, understanding of how to
conserve aquatic genetic resources remains
weak. Most assumptions derive from
experience with other organisms and
theoretical speculation (Frankel and Sould
1981; Nelson and Soul4 1987). The con-
servation ofcultured fish genetic resources
can use similar approaches to those ap-
plied for the conservation of genetic re-
sources offarm animals (Siler et al. 1984).
There has been increasing interest in
conservation of fish genetic resources in
the last decade as evidenced by numerous
national and international meetings (e.g.,
FAOLJNEP 1981; Ryman 1981; STOCS
1981;Pullin1988;DasandJhingran1989;
Prace VurhVodnany 1989; Billington and
Hebert 1991; ICLARM 1992). An expert
consultation on "Utilization and conser-
vation of aquatic genetic resources" was
organized by FA0 in November 1992 in
Rome.
There are at present two main fields
in aquaculture genetic research: genetic
characterization of farmed stocks and