biotechnology. Although there is an exten-
sive literature on the theory of breeding
plans and their application to livestock
and plant production, little attention has
yet been given to this in aquaculture (Gall
1990).
Manipulation of genotypes for produc-
tion purposes and conservation of genetic
resources in nondomesticated populations
should be complementary. Human activi-
ties have strong impacts on aquatic ge-
neticresources. Artificial selection may be
intentional (through fisheries management
and by selection of broodstock) or unin-
tentional (where no specific breeding goals
exist, but the culturist must still choose
broodstock). For example, the larger in-
dividuals may be removed from apond and
sent to market and the smaller fish used
for restocking.Genetic Characterization
General Considerations
A prerequisite to gene pool conserva-
tion is the characterization of the genetic
structure of populations (FAOAJNEP
1981 1. Wild and farmed populations should
be monitored to determine their genetic
structure. Indeed, to manipulate better
the variation associated with quantitative
genetic traits in captive fish populations,
aquaculture geneticists should understand
the source of the variation of such traits
(Robinson and Doyle 1990). Moreover,
ecological and taxonomical studies are
required, particularly in tropical regions
where most ecosystems are poorly under-
stood and many species still undescribed
(FAO/UNEP 1981). In freshwaters, data
should be collected within localities, be-
tween localities within a drainage system,
and between drainage systems (Meffe
1986). Documentation of aquatic genetic
resources includes database development
and circulation of literature.
Genetic analyses can provide impor-
tant information on the taxonomic status
of populations. Some landlocked forms of
Salmo salar in North America were for-
merly given subspecific status (S. salar
sebago). This was not confirmed by protein
polymorphism and mtDNAanalyses (Stahl
1983,1987; Birt et al. 1986). This species
is better considered as comprising thou-
sands of reproductively isolated breeding
groups, the adults having strong homing
behavior, returning to spawn in their natal
rivers (Davidson et al. 1989).
Many techniques are used in the
characterization of fish genetic resources.
In the last decade, new techniques from
molecular biology have been introduced.
Although any one technique can provide
interesting data, a multitechnique ap-
proach is better (Chevassus and Coche
1986; Cataudella et al. 1987). Compara-
tive analyses of electrophoretic, meristic
and morphological variation should be
carried out to ensure unbiased estimates
of genetic variation (FAOAJNEP 1981).
These techniques facilitate detection of
genetic markers that are characteristic of
some stocks, in order to monitor quanti-
tative and qualitative genetic changes.
Genetic markers can be used to label
specific hatchery strains or natural
populations unambiguously, or even as
identification systems forpatentingstrains
(Gyllensten and Wilson 1987). The main
genetic markers of fish are morphological
characteristics, isozymes and
mitochondria1 DNA.Multivariate Analysis of
Morphometric and Meristic Data
Multivariate analysis ofmorphometric
and meristic data is less expensive and
laborious than electrophoresis andisuseful
for defining taxa and forms. However, it
must be carefully analyzed, as the expres-
sion of gene action on morphological
characters is greatly influenced by envi-
ronmental conditions (phenotypic plastic-
ity). Sometimes, morphological analyses
enable the detection of variation in fish