Acipenseridae, Bonaparte, 1831

Freyhof, JÖrg, Yoğurtçuoğlu, Baran, Jouladeh-Roudbar, Arash & Kaya, Cüneyt, 2025, Handbook of Freshwater Fishes of West Asia, De Gruyter : 46-48

Family Acipenseridae

Sturgeons

Sturgeons are a small family restricted to the northern hemisphere, in Europe, northern Asia, and North America. Traditionally,all sturgeon species found in Western Asia and Europe were placed in two genera: Acipenser (nine species) and Huso (one species). Other genera in the family Acipenseridae include Scaphirhynchus , with three species in North America, and Pseudoscaphirhynchus , with 1-3 species in the Aral basin in Central Asia. The phylogeny of sturgeons has been well understood for many years, and it has long been evident that the genus Acipenser is paraphyletic. This has not been reflected into a generic classification, as species such as Sterletus stellatus have been found to occupy different positions in different analyses. Therefore, sturgeon phylogeny was considered preliminary. This was also intended to avoid renaming these highly threatened species, as it was feared that name changes would hinder sturgeon protection. Sturgeon phylogeny has recently been reanalysed and, for the first time, translated into a new generic structure. Pseudoscaphirhynchus and Scaphirhynchus remain valid genera, but Acipenser now comprises only A. sturio , A. desotoi and A. oxyrinchus . All other West Asian and European Acipenser species have been placed in the genus Huso , ignoring that Huso is a junior synonym of Sterletus . The type species of Sterletus is the American lake sturgeon ( S. fulvescens ). Consequently, all sturgeon species in the Pacific basin in Asia and America, including Huso dauricus, have been placed in the genus Sinosturio . Users of species names now have three options: 1) treat the knowledge of sturgeon phylogeny still as too incomplete to risk causing confusion by changing the names, 2) place all sturgeons in the family Acipenseridae in the genus Acipenser (requiring few name changes), or 3) accept the proposed generic concept, as we do in this book.

Sturgeons are a very isolated group of fishes resembling sharks with a heterocercal caudal, a largely cartilaginous skeleton, and an intestine with a spiral valve. The earliest fossil sturgeon is Protopsephurus from the Barremian (126.5– 121.4 million years ago) in the Cretaceous of China.Sturgeons are large fish with five rows of hard bony plates, no scales, four barbels, a projecting snout, and an inferior mouth forming a protrusible tube. Bony plates or scutes are more prominent in small individuals, often partly hidden under the skin in adults. Most sturgeons are anadromous, foraging in marine waters or freshened parts of seas and undertaking long spawning migrations to large rivers. Upstream migration generally starts in late summer and is less marked when temperatures fall below a threshold. Many individuals overwinter in freshwater. The main peak of upstream migration usually occurs in early spring. The individuals returning to rivers in late summer often move and spawn further upstream than those migrating in spring. All species spawn in freshwaters in spring and summer. Spawning generally takes place in fast-flowing water, on gravel bottom. Females return to foraging areas immediately after spawning, while males often remain at the spawning grounds for many weeks, waiting for other females. Females of most species do not spawn every year. Eggs and larvae are very sensitive to low oxygen concentrations.The juveniles of anadromous species usually migrate to the sea during their first summer. All sturgeons can complete their life cycles in pure freshwater, and non-anadromous, riverine individuals or populations existed in S. nudiventris and S. gueldenstaedtii .

Among all Western Palaearctic fishes, sturgeons are the family most strongly impacted by human activities such as damming and overfishing. All anadromous sturgeons are now very rare in the Black Sea basin, following the impoundment of almost all spawning rivers. It is also evident that nearly all individuals found today descend from stocked juveniles produced in sturgeon farms. The last Black Sea tributaries that still support natural migrating populations are the Danube and the Rioni ( Georgia). The Rioni is the key river in the Black Sea basin, home to the last populations of S. nudiventris (if still extant) and S. persicus . Despite their critical status these species are still overfished in the Rioni. The Caspian sturgeon populations are under immense pressure due to overfishing and the loss of spawning sites. It is clear that, except for S. stellatus , all anadromous sturgeons discussed in this book now completely depend on stocking. Overfishing at sea for meat and in rivers for caviar has resulted in their extinction. Indeed, sturgeons are a conservation success story, as most species would be completely extinct today without farming and stocking. Populations depend on stocking of juveniles from fish farms. This makes identification even more problematic as most sturgeon farms produce different hybrids. The most frequent hybrid is a cross between S. huso and S. ruthenus (called “bester”). Furthermore, non-native species such as S. baerii and different American species are widely produced and stocked. Fish farms in the Black and Caspian Seas used wild-caught genitors. As these are increasingly difficult to find, farms gradually shift to in-farm spawners. It is common for S. persicus outside their main distribution range to be confused with S. gueldenstaedtii by sturgeon farmers, who often mix them with this species.

Further reading. Holčík et al. 1989a (biology, systematics); Birstein & Bemis 1997 (biology, conservation); Elvira 2000 (conservation); Pikitch et al. 2005 (conservation, fisheries); Krieger et al. 2008 (molecular phylogeny); Havelka et al. 2011 (cytogenetics); Near & Thacker 2024 (fossil); Brownstein & Near 2025 (generic concept); Kottelat & Freyhof 2025 ( Sterletus vs. Huso ).

Scute terminology in Acipenseridae . A series of scutes or bony plates partially cover the body of a sturgeon. The scutes are more prominent in juveniles and become embedded and reduced as they grow. Scutes are most deeply embedded and reduced in adult S. huso . Scutes are arranged in five longitudinal rows, one row along the dorsal midline between the head and the dorsal origin (dorsal scutes), one midlateral row from the head to the caudal (lateral scutes), and one row between the pectoral base and the anal origin (ventral scutes). Rhombic or star-shaped bony denticles may be present at least between the dorsal and lateral scute rows; some denticles are enlarged to form plates, especially in the posterior part of the body. These denticles are very prominent in juveniles of S. stellatus , S. gueldenstaedtii , and S. persicus but become relatively smaller and often deeply embedded in adults. In other species, denticles are often absent or very small. In Acipenser sturio , the denticles are more prominent, large, and clearly visible in adults. All scutes and denticles may be lacking in some individuals of all species.

Key to species of Acipenseridae in West Asia

1a - Gill membranes joined broadly to each other and free from isthmus; mouth very large, crescent-shaped. ……………… S. huso

1b - Gill membranes attached to isthmus and not joined to each other and attached to isthmus; mouth small and straight. ………………2

2a - Lower lip continuous, not interrupted in middle; first dorsal scute larger than following ones, fused with head, forming an obtuse angle with head profile; barbels fimbriate. ……………… S. nudiventris

2b - Lower lip interrupted in middle; first dorsal scute not larger than following ones; barbels fimbriate or not. ………………3

3a - 20–49 fan-shaped gill rakers terminated by several tubercles; 32–62 lateral scutes. ……………… S. baerii

3b - 15–35 rod-shaped gill rakers; 23–50 lateral scutes. ………………4

4a - Rhombic or elongated denticles between dorsal and lateral scutes; a series of plates along posterior part of anal base; 2–4 plates along lower edge of caudal peduncle. ……………… A. sturio

4b - Star-shaped or roundish denticles between dorsal and lateral scutes; no plates along posterior part of anal base; 0–1 plate along lower edge of caudal peduncle. ………………5

5a - Base of barbels closer to mouth than to tip of snout; snout very long (59–65 % HL), narrow, depressed. ……………… S. stellatus

5b - Base of barbels closer to tip of snout than to mouth; snout short (22–36 % HL) and blunt. ………………6

6a - Head triangular, if seen from below (Figure 28); dorsal profiles of head and body forming an obtuse angle; belly yellowish-white; dorsum golden brown; snout short, blunt and somewhat rounded, its depth at eye about equal to or smaller than its length. ……………… S. gueldenstaedtii

6b - Head squarish, if seen from below (Figure 28); dorsal profiles of head and body continuous; belly white; dorsum greyish-blue to black; snout elongate massive and curved downward, its depth at eye smaller than its length. ……………… S. persicus