salmonid

Salmonidae Fossil range: Upper Cretaceous–Recent PreЄ Є O S D C P T J K Pg N [1]
Chinook salmon (Oncorhynchus tschawytscha)
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Superorder: Protacanthopterygii Order: Salmoniformes Family: Salmonidae
Genera
(see text)

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.^[2] Although the smallest species is just 13 centimetres (5.1 in) long as an adult, most are much larger, and the largest can reach 2 metres (6.6 ft).^[1]

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.^[2]

Evolution of Salmonidae

Current salmonids arose from three lineages: whitefish (Coregoninae), graylings (Thymallinae), and the char, trout and salmons (Salmonidae). Generally, it is accepted that all three lineages share a suite of derived traits indicating a monophyletic group.^[3]

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.^[3]

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.^[4] Several of these species appear to be Oncorhynchus—the current family for trout, char and Pacific salmon. 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.).^[3][5]

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.^[3] 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.^[5]

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.^[6] 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:^[1]

Order Salmoniformes

• Family: Salmonidae
  • Subfamily: Coregoninae
    • Coregonus - Whitefishes (70 species)
    • Prosopium - round whitefishes (6 species)
    • Stenodus - inconnu (1 species)
  • Subfamily: Thymallinae
    • Thymallus - Graylings (12 species)
  • Subfamily: Salmoninae
    • Brachymystax - lenoks (3 species)
    • Hucho (5 species)
    • Oncorhynchus - Pacific salmon and trout (14 species)
    • Parahucho
    • Salmo - Atlantic salmon and trout (29 species)
    • Salvelinus - Char and trout (e.g. Brook trout, Lake trout) (49 species)
    • Salvethymus (1 species)

Notes

References

Wikimedia Commons has media related to: Salmonidae

• 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
• "Salmonidae". FishBase. Ed. Rainer Froese and Daniel Pauly. October 2004 version. N.p.: FishBase, 2004.
• Salmonidae (TSN 161931). Integrated Taxonomic Information System. Retrieved on 12 December 2004.
• "Salmoniformes". FishBase. Ed. Ranier Froese and Daniel Pauly. October 2004 version. N.p.: FishBase, 2004.