| Osmeriformes | |
|---|---|
 | |
| Delta smelt,Hypomesus transpacificus (Osmeroidei:Osmeridae) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Superorder: | Osmeromorpha |
| Order: | Osmeriformes Regan, 1913[1] |
| Type species | |
| Salmo eperlanus | |
| Families | |
TheOsmeriformes/ɒsˈmɛrəfɔːrmiːz/ are anorder ofray-finned fish that includes thetrue orfreshwater smelts and allies, such as thenoodlefishes; they are also collectively calledosmeriforms. They belong to theteleostsuperorderProtacanthopterygii, which also includespike andsalmon, among others.[2] The order's name means "smelt-shaped", fromOsmerus (thetype genus) + the standardfish ordersuffix "-formes". It ultimately derives fromAncient Greekosmé (ὀσμή, "pungent smell") +Latinforma ("external form"), the former in reference to the characteristic aroma of the flesh ofOsmerus.[3][4][5]
In the classification used here, the order Osmeriformes contains twosuborders, fourfamilies, some 17 genera, and about 52species.[6] The "marine" smelts and allies (e.g. the odd-lookingbarreleyes) were formerly included here as suborder Argentinoidei; they are now usually considered more distantly related than it was believed and treated as orderArgentiniformes. When the marine smelts were included here, the subdivisions of the Osmeriformes were down-ranked by one.[7] Thegalaxiids were also previously placed in this order, being treated as allied with the retropinnids, but are now known to represent their own, distinct order.[8]
Osmeriformes are small to mid-sized slender fish. Theirmaxilla is usually included in the mouth's gape, and most of them have anadipose fin as is often found in theProtacanthopterygii. Their [pterosphenoid] usually has aventral flange, and thevomer has a shortposterior shaft. They have reduced or even missingarticular andmesopterygoid teeth, and the basisphenoid and orbitosphenoid bones are entirely absent. Theirscales lack radii.[7]
Despite the term "freshwater smelts", the members of the Osmeriformes are generallymarine,amphidromous oranadromous migrants. Even the sedentary freshwater species in this family are usually tolerant of considerable changes insalinity. Almost all osmeriformsspawn in fresh water, thus the marine species are generallyanadromous. They are found intemperate oceans worldwide and in temperatefreshwater of theHolarctic and around theSouth Pacific region; only a handful ofspecies occur intropical waters. Theeggs are surrounded by an adhesivemembrane.[7]
With theArgentiniformes,Alepocephaliformes,Galaxiiformes, andLepidogalaxiiformes separated as distinct orders, the remaining Osmeriformes appear to be amonophyletic group. Asprotacanthopterygians, they are known to be related to theSalmoniformes (pikes andsalmon). However, more recent studies incorporatinganatomical andDNA sequence data suggest that their closest relatives are the deep-seaStomiiformes.[9][10][11]
The classification of the Osmeriformes as approached here is:[6][10][12]
A possiblefossil osmeriform isSpaniodon, apiscivore fromLate Cretaceous seas.[9] The group originated probably somewhat earlier, but aCretaceous age maybe about 110million years ago or so is likely.[5][7] The oldest definite osmeriform isSpeirsaenigma from thePaleocene ofAlberta, Canada, which was a relative of the modern ayu fish and appears to have been a freshwater species.[14][15] In 2025, a new, extinct family of freshwater Southern Hemisphere smelt, theFerruaspidae, was identified from theMiocene-agedMcGraths Flat fossil site of Australia.[13]
The familiesGalaxiidae andLepidogalaxiidae were at one time placed together withRetropinnidae in the sub order Galaxoidei, however with new molecular studies they have been elevated to the ordinal level.[12]
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