Sturgeon


”Sturgeon” is the common name for the 27 species of fish belonging to the family Acipenseridae. The earliest sturgeon fossils date to the Late Cretaceous, and are descended from other, earlier acipenseriform fish, which date back to the Early Jurassic period, some 174 to 201 million years ago. They are one of two living families of the Acipenseriformes alongside paddlefish. The family is grouped into five genera: Acipenser, Huso, Scaphirhynchus, ''Sinosturio, and Pseudoscaphirhynchus''. Two species may be extinct in the wild, and one may be entirely extinct. Sturgeons are native to subtropical, temperate and sub-Arctic rivers, lakes and coastlines of Eurasia and North America. A Maastrichtian-age fossil found in Morocco shows that they also once lived in northern Africa during the Cretaceous.
Sturgeons are long-lived, late-maturing fishes with distinctive characteristics, such as a heterocercal caudal fin similar to those of sharks, and an elongated, spindle-like body that is smooth-skinned, scaleless, and armored with five lateral rows of bony plates called scutes. Several species can grow quite large, typically ranging in length. The largest sturgeon on record was a beluga female captured in the Volga Delta in 1827, measuring long and weighing. Most sturgeons are anadromous bottom-feeders, migrating upstream to spawn but spending most of their lives feeding in river deltas and estuaries. Some species inhabit freshwater environments exclusively, while others primarily inhabit marine environments near coastal areas, and are known to venture into open ocean.
Several species of sturgeon are harvested for their roe, which is processed into the luxury food caviar. This has led to serious overexploitation, which combined with other conservation threats, has brought most of the species to critically endangered status, at the edge of extinction.

Etymology

The English word Sturgeon comes from Middle English sturgiun itself from Old French estorjoun, displacing Old English styrġa though both are derived from Proto-Germanic *sturjô.
Apparent cognates to Sturgeon might be found in Baltic, Germanic, Greek, Romance, and Slavic languages. The trade of sturgeon in ancient Europe would cause for the root word for these to spread across the region. Many potential reconstructions may place it as either a non-Indo-European substrate language, possibly from around the Volga river where sturgeon could be caught and sold, while others reconstruct a Proto-Indo-European source.
One reconstruction links Sturgeon to ultimately derive from Proto-Indo-European *str̥yón-.

Evolution

Fossil history

fishes appeared in the fossil record some 174 to 201 million years ago, during the Early Jurassic, making them some of the earliest extant actinopterygian fishes. Sturgeons must have diverged from their closest relatives, the paddlefish, during the Early Cretaceous or prior, as the earliest fossil paddlefish is known from then. True sturgeons appear in the fossil record during the Upper Cretaceous, with amongst the oldest known remains being a partial skull from the Cenomanian of Alberta, Canada. In that time, sturgeons have undergone remarkably little morphological change, indicating their evolution has been exceptionally slow and earning them informal status as living fossils. This is explained in part by the long generation interval, tolerance for wide ranges of temperature and salinity, lack of predators due to size and bony plated armor, or scutes, and the abundance of prey items in the benthic environment. They do, however, still share several primitive characteristics, such as heterocercal tail, reduced squamation, more fin rays than supporting bony elements, and unique jaw suspension.

Phylogeny and taxonomy

Despite the existence of a fossil record, full classification and phylogeny of the sturgeon species has been difficult to determine, in part due to the high individual and ontogenic variation, including geographical clines in certain features, such as rostrum shape, number of scutes, and body length. A further confounding factor is the peculiar ability of sturgeons to produce reproductively viable hybrids, even between species assigned to different genera. While ray-finned fishes have a long evolutionary history culminating in the most familiar fishes, past adaptive evolutionary radiations have left only a few survivors, such as sturgeons and gars.
The phylogeny of Acipenseridae, as in the cladogram, shows that they evolved from the bony fishes. In currently accepted taxonomy, the class Actinopterygii and the order Acipenseriformes are both clades. Approximate dates are from Near et al., 2012.
The wide range of the acipenserids and their endangered status have made collection of systematic materials difficult. The factors have led researchers in the past to identify over 40 additional species that were rejected by later scientists. An effort is ongoing to resolve the taxonomic confusion using a continuing synthesis of systematic data and molecular techniques.
Sturgeons are a highly morphologically conservative group, to the extent that lineages that have been separate since the Cretaceous period can physically appear very similar, and mistakenly classified as each other's closest relatives. In the classic taxonomic treatment, Acipenseridae was subdivided into 2 subfamilies; Acipenserinae, including the genera Acipenser and Huso, and Scaphirhynchinae, including the genera Scaphirhynchus and Pseudoscaphirhynchus. Under a phylogeny that exclusively incorporates morphological data, sturgeons appear to comprise two groups that diverged during the Cretaceous: a Scaphirhynchus lineage, and a Acipenser+''Huso+Pseudoscaphirhynchus lineage. The latter seemingly appears rather young compared to the age of the group as a whole, with much of its radiation only occurring during the Late Paleogene and Neogene.
However, with the advent of molecular phylogenetics, multiple studies since the 1990s have recovered this arrangement as paraphyletic, instead finding A. oxyrhinchus and A. sturio to form the most basal clade among sturgeons, and all other species being in a separate clade, with the various other species of Acipenser, Scaphirhynchus, Pseudoscaphirhynchus, and Huso to have varying levels of relationship with one another. The morphologically distinct "shovelnose" type sturgeons are deeply nested within the former "Acipenser" and "Huso" clades. The divergences within the group have also been found to be much deeper, with Acipenser sensu stricto diverging from the rest of the group well into the Cretaceous. The other lineages were found to have diverged from one another during the Late Cretaceous and Paleogene.
The exact placement of Scaphirhynchus varies depending on the study and the methods used, with some placing it within the second-most basal clade comprising primarily Pacific species, whereas others place it in its own clade that is more derived than the secondmost basal clade but less derived than the most derived Atlantic and Central Asian clade. No studies have yet delineated a relationship between it and Pseudoscaphirhynchus. In addition, the exact relationships of the members of the most derived, primarily Atlantic clade vary, although most analyses at least find all the species in it to form a monophyletic clade. The placement of A. sinensis also varies by the study, with some placing it as the only Pacific member of the otherwise Atlantic-based most-derived clade, whereas others place it with the rest of the Pacific sturgeons as a sister to A. dabryanus.
Brownstein & Near used DNA sequencing and morphological data to establish 5 monophyletic genera for Acipenseridae and mostly resolve the longstanding confusion over clade names. The 5 clades found were Acipenser sensu stricto, Scaphirhynchus, Pseudoscaphirhynchus, Huso, and the revived genus Sinosturio, as well as moving species out of Acipenser'' and into the latter two genera.
The following taxonomy is based on Brownstein & Near, 2025:

Species

The family contains 27 recent species in 5 genera, as well as a number of fossil species and genera.
The following classification is based on Eschmeyer's Catalog of Fishes :
File:Huge sturgeon in the Gulf of St. Lawrence ecosystem - panoramio.jpg|thumb|The Atlantic sturgeon is one of the most basal sturgeon species
Family Acipenseridae
  • Genus Acipenser Linnaeus, 1758
  • * Acipenser desotoi Vladykov, 1955
  • * Acipenser oxyrinchus Mitchill, 1815
  • * Acipenser sturio Linnaeus, 1758
  • Genus Scaphirhynchus Heckel, 1835
  • * Scaphirhynchus albus
  • * Scaphirhynchus platorynchus
  • * Scaphirhynchus suttkusi J. D. Williams & Clemmer, 1991
  • Genus Sinosturio Jaekel in Weigelt, 1929
  • *Sinosturio ''dabryanus
  • *Sinosturio dauricus
  • * Sinosturio medirostris
  • * Sinosturio mikadoi
  • * Sinosturio schrenckii
  • * Sinosturio sinensis
  • * Sinosturio transmontanus
  • Genus Huso J. F. Brandt & Ratzeburg, 1833
  • * Huso baerii
  • ** Huso baerii baicalensis
  • ** Huso baerii stenorrhynchus
  • * Huso brevirostrum
  • * Huso colchicus
  • * Huso fulvescens
  • * Huso gueldenstaedtii
  • * Huso huso
  • * Huso naccarii
  • * Huso nudiventris
  • * Huso persicus
  • * Huso ruthenus
  • * Huso stellatus
  • Genus Pseudoscaphirhynchus Nikolskii, 1900
  • * Pseudoscaphirhynchus fedtschenkoi
  • * Pseudoscaphirhynchus hermanni
  • * Pseudoscaphirhynchus kaufmanni''