By James E. Lannan, Emeritus Professor of Fisheries
Oregon State University
One element of contention about the use of salmon hatcheries is the question of whether
hatchery-bred salmon differ genetically from naturally spawning "wild" salmon.
Disagreement on this subject is partly semantic, because the term "genetic
difference" is used in different contexts when referring to the individual and
population levels of biological organization.
Definition of terms
The gene is the fundamental unit of heredity. The following definition is
from the widely used genetics textbook by Strickberger:
The modern science of'genetics originated when Gregor Mendel discovered that hereditary
characteristics are determined by elementary units transmitted between generations in a
uniform predictable fashion. Each such unit, which can be called a genetic unit, or gene,
is a substance that must satisfy at least two essential requirements: (1) that it is
inherited between generations in such fashion that each descendant has a physical copy of
this material, and (2) that it provide information to its carriers in respect to
structure, function, and other biological attributes.
The term genome describes the set of genes possessed by an organism. All members
of a species are endowed with the same set of genes.
The term allele refers to different forms of a gene. Some genes occur in
two or more forms. Familiar examples of human genes that have more than one form are the
genes for eye color and ABO blood type. Brown and blue eyes are alleles of a gene that
determines eye color. Similarly, blood types A, B, and 0 are alleles of a single gene.
A gene pool is the totality of genetic material possessed by a species. The gene
pool of any species contains the instructions for all the inherited traits that the
species is capable of expressing. These instructions are the genetic resources of
the species. When genetic resources are lost from a gene pool, options for surviving and
reproducing may also be lost. As these options diminish, the probability of becoming
extinct increases. When genetic resources are lost from a species gene pool, they can
not be restored.
Genetic difference at the level of individual fish
At the level of individual fish, two animals are genetically different if one
individual possess an allele or alleles that the other does not. Therefore, the statement,
"hatchery fish are genetically different from wild fish," is true if and only if
there is an allele or alleles that occurs only in hatchery-bred fish, and a complimentary
allele or alleles that occur only in "wild", naturally spawned fish. No such
alleles are known to exist, and probably do not exist in nature. As a class, hatchery fish
are not genetically different from "wild" fish.
Hatchery-bred fish are descended from naturally spawning "wild" fish and
possess all the genes found in "wild" fish. There is no known genetic mechanism
that would result in the creation of an allele found only in artificially propagated fish.
Further, there is no known mechanism that would preclude the hatchery allele, if one
existed, from being introduced into naturally spawning populations when fish of hatchery
origin spawn naturally.
Genetic differences at the population level
At the population level, differences in the frequencies of inherited traits are often
observed between naturally spawning populations, between hatchery populations, and between
hatchery and naturally spawning populations. These differences in frequencies are referred
to as genetic differences because they describe variation in the organization of genetic
material among populations. This type of genetic variation arises because of
different genetic histories of the populations since their divergence from a common
ancestral population.
Genetic management of naturally spawning populations is not possible, but artificially
propagated populations are amenable to genetic management. The frequencies of inherited
traits in hatchery populations can be adjusted to suit management goals and objectives.
Establishing and maintaining hatchery populations with a prescribed pattern of life
history variation similar or identical to the naturally spawning populations with which
they may interbreed is an attainable management goal that could ameliorate concerns about
detrimental interactions.
Summary
At the level of individual fish, there is no genetic difference between
naturally-spawned and hatchery-bred salmon. At the population level, there may be
differences in the frequencies of inherited traits between populations.
February 2001