Salmonidae is a
family of
ray-finned fish, the only living family of
the
order
Salmoniformes. It includes
salmon,
trout,
chars,
freshwater
whitefishes and
graylings. The
Atlantic salmon and trout of
genus
Salmo give the family and order their
names.
Salmonids have a relatively primitive appearance among the
teleost fish, with the
pelvic
fins being placed far back, and an
adipose fin towards the rear of the back. They
are slender fish, with rounded scales and a forked tail. Their
mouths contain a single row of sharp teeth. Although the smallest
species is just long as an adult, most are much larger, and the
largest can reach .
All salmonids spawn in fresh water, but in many cases, the fish
spend most of their life at sea, returning to the rivers only to
reproduce. This type of life cycle is described as
anadromous. They are
predators, feeding on small crustaceans, aquatic
insects, and smaller fish.
Evolution of Salmonidae
Current salmonids arose from three
lineages:
whitefish (
Coregoninae),
graylings (
Thymallinae), and the
char,
trout and
salmons (
Salmoninae). Generally, it is accepted that all
three lineages share a suite of derived traits indicating a
monophyletic group.
Salmonidae first became evident in
the middle Eocene with the fossil Eosalmo driftwoodensis (discovered in
Driftwood Creek, central British Columbia
). This fossil shares traits found in the
salmoninae, whitefish and grayline lineages. Hence,
E.
driftwoodensis is an archaic salmonid, representing an
important stage in salmonid evolution.
A gap
appears in the salmonine fossil record after E.
driftwoodensis; until the late Miocene
(~7 m.y.a.) trout-like fossils appear in Idaho
, in the
Clarkia Lake
beds
. Several of these species appear to be
Oncorhynchus—the current genus
for Pacific salmon and some trout. The presence of these species so
far inland established that
Oncorhynchus was not only
present in the Pacific drainages before the beginning of the
Pliocene (~5-6 m.y.a.), but also that
rainbow and
cutthroat trout, and Pacific salmon lineages
had diverged before the beginning of the Pliocene. Consequently,
the split between
Oncorhynchus and
Salmo (Atlantic salmon) must have occurred well
before the Pliocene. Suggestions have gone back as far as the early
Miocene (~20 m.y.a.).
Speciation among
Oncorhynchus
has been examined for decades, and to this day, a family "tree" is
not completely developed for the Pacific salmonids.
Mitochondrial DNA (mtDNA) research has
been completed on a variety of Pacific trout and salmonid species,
but the results do not necessarily agree with fossil research, or
molecular research. It is generally agreed that
chum,
pink and
sockeye salmon lineages diverged in
the sequence after other species. Montgomery (2000) discusses the
pattern of the fossil record as compared to
tectonic shifts in the plates of the
Pacific Northwest America. The (potential)
divergence in
Onchorhyncus
lineages appear to follow the uprising of the
Pacific Rim. The climatic and habitat changes
that would follow such a geologic event are discussed, in the
context of potential stressors leading to adaptation and
speciation.
One interesting case involving speciation with salmon is that of
the Kokanee, sockeye that have been
landlocked. Kokanee sockeye evolve differently
from
anadromous
sockeye—they reach the level of "biological species". Biological
species—as opposed to
morphological species—are defined by
the capacity to maintain themselves in
sympatry as independent
genetic entities. This definition can be vexing
because it appears that it does apply only to sympatry, and this
limitation makes the definition difficult to apply.
There are examples in
Washington, Canada
and
elsewhere where two populations live in the same lake but spawn in different substrates, at different
times, and eat different food sources. There is no pressure
to compete or interbreed (two responses when resources are short).
These types of Kokanee salmon show the principal attributes of a
biological species: they are reproductively isolated and show
strong resources partitioning.
Classification
Together with the closely-related
Esociformes (the pikes and related fishes) and
Osmeriformes (e.g.
smelts), the Salmoniformes comprise the
superorder Protacanthopterygii.
The Salmonidae (and Salmoniformes) are divided into three
subfamilies and around ten genera:
Order
Salmoniformes
Notes
References
- Behnke, Robert J. Trout and Salmon of North America,
Illustrated by Joseph R. Tomelleri. 1st Chanticleer Press ed. New
York: The Free Press, 2002. ISBN 0-7432-2220-2
- Dushkina, L.A. Farming of Salmonids in Russia,
Aquaculture & Fisheries Management; Jan1994, Vol. 25 Issue 1,
p121-126
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