7937

• UCREFRP Catalog Number: 7937
• Author: Chart, T. E. and E. P. Bergerson.
• Title: Methods for Long-term Identification of Salmonids
• USFW Year: 1988.
• USFW - Doc Type: A Review.
• Copyright Material: NO

Allendorf and Phelps 1980,1981a;Cross and King 1983;
Stahl 1983). Recent studies have shown that
reproductive units of Atlantic salmon with morphologic
and genetic differences still exist in Scandinavia and
other pazts of the world (Ryman and Stah11981; Thorpe
and Mitchell 1981). In the River Alta, north Norway,
three appazently genetically undisturbed (Heggberget
et al. 1986) populations of Atlantic salmon were
detected on the basis of difference in growth patterns,
corroborated by differences in allelic frequencies.
Electrophoresis generates lazge volumes of data on
genotypic and allelic frequency; however, much of the
genetic variation in fish remains undetected. Current
technology is expanding to reveal previously undetected
alleles through techniques such as the modification of
buffer and gel concentrations and testing of different
thermal stabilities of proteins (Singh et a1.1976; Coyne
1982) and enzyme analysis of mitochondrial DNA
(Utter et al. 1987). Polyacrylamide and starch gel
electrophoresis and isoelectric focusing provide the
reseazcher with useful tools to identify stocks of fish
under many circumstances; however, the techniques
have limitations, as do all other methods of fish
identification.
Genetic Tagging
The intentional manipulation of naturally occurring
allelic variation through artificial propagation programs
has been explored as an alternative to physical tagging as
a means of identifying stocks of fish (Schweigert et al.
1977; Grant et al. 1980; Murphy et al. 1983; Beacham et
a1.1985). Differences in protein structure that are caused
by genetic variation and that have been identified
eledrophoretically are generally inherited according to
simple Mendelian principles (Seeb et al. 1986). Allelic
frequencies often differ in reproductively isolated
salmonid populations, and thus provide an opportunity
for generic marking (Allendorf and Utter 1979).
Genetic marking has been applied to freshwater
species other than sahnonids, including walleye,
Stizostedion vitreum vitreum (Clayton et al. 1974;
Murphy et al. 1983); common carp, Cyprinus carpio
(Moav et x1.1976), and largemouth bass (Carmichael et
x1.1986; Williamson et x1.1986).
In a lazge-scale, production-oriented study by Seeb
et al. (1986), in which chum salmon of Kennedy Creek,
WA, were genetically marked, electrophoretic
techniques described by May et al. (1979) were used to
detect polymorphisms at gene loci in extracted eye and
muscle tissue. Two loci from the muscle tissue that
expressed relatively low frequency alleles were chosen
for the genetic markers. In a genetically structured
breeding program stazted in 1976 and continued
thereafter, 20% of the total 1980 chum salmon run in
Kennedy Creek was genetically mazked and 29% in
1981. Knowing the number of mazked juveniles released
enabled researchers to estimate the number of juvenile
chum salmon produced in the area.
Taggart and Ferguson (1984) identified an allele of
limited distribution among native brown trout (Salmo
hutta) in Great Britain and Ireland that was also present
in low frequencies in hatchery stocks. They suggested
breeding homozygosity for this hatchery-specific allele,
which would provide a useful mark in identifying the
hatchery stock.
Sahnonid species are particularly suited for
biochemical stock identification because they show a
relatively high degree of protein polymorphism and
substantial heterogeneity among populations (Utter et
a1.1980; Ryman 1983). Electrophoretic identification of
component stocks from ocean commercial catches has
been reported for a number of anadromous salmonid
species (Nyman and Pippy 1972; Allendorf and Utter
1979; Grant et a1.1980; Payne 1980; Milner et al. 1983).
Genetic marking has advantages and disadvantages
(summary follows), compared with standard tagging
procedures (Taggart and Ferguson 1984; Seeb et al.
1986).
Advantages
Genetic tagging lacks the following limitations of
standard tagging procedures.
1. The inability to mark tiny larvae (Jamieson 1974;
Hedgecock et a1.1976).
2. The potential loss of the mark through fin
regeneration, brand illegibility, or tag loss (Stuart 1958;
Foerster 1968; Ricker 1975).
3. Differential mortality as a result of the tag or tagging
procedure (Foerster 1936; Ricker 1975).
4. Differential mark recovery resulting from altered
behavior in the tagged group (Ricker 1975).
Disadvantages
1. When the genotype is altered, stocks of fish-not
individuals-aze "tagged," and recoveries are assigned
to that stock on the basis of probabilities.
2. When genetically tagging a population of fish, the
researcher must consider to what degree that
population might be inbreeding. Ryman and Stahl
(1980) suggested using no fewer than 30 fish of the least
numerous sex in any one generation.
3. A final consideration in genetic marking was raised
by Allendorf and Utter (1979) when they proposed that
a potential genetic pitfall may lie in breeding a strain of
fish homorygous to a rare allele if that allele (or one
linked to it) causes some survival disadvantage to its
carriers. In other words, this allele may have been rare
for this very reason. Kimura (1983), however, contended
that rare alleles are typically at structural loci and are
wnsidered structurally neutral.
Genetic tagging provides a method whereby allelic
frequency may be stabilized in the hatchery system,
enabling an estimate of the intentional or unintentional
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