Acipenser naccarii | |
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Adriatic sturgeon with sea lampreys in the Aquarium Finisterrae, Spain | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Actinopterygii |
Order: | Acipenseriformes |
Family: | Acipenseridae |
Genus: | Acipenser |
Species: | A. naccarii |
Binomial name | |
Acipenser naccarii Bonaparte 1836 | |
Synonyms [3] [4] | |
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The Adriatic sturgeon (Acipenser naccarii) is a species of fish in the family Acipenseridae. It is native to the Adriatic Sea and large rivers which flow in it of Albania, Greece, Italy, Montenegro, Croatia, Bosnia and Herzegovina and Slovenia. Specimens can be seen in several public aquarium, such the Milan Aquarium, Aquarium Finisterrae, Aquarium of the Po, and Oasis of Sant'Alessio in Lombardy.
The Adriatic sturgeon reaches a maximum length exceeding 2 m (6.6 ft); the published maximum weight was 25 kg (55 lb), but large wild fish recently caught were evidently exceeding 40 kg (88 lb).
Like other sturgeons it has an elongated body, heterocercal tail, partially cartilaginous skeleton, naked skin and longitudinal series of bony scutes on the body. The rostrum is tendentially conical and rather short (1/3 of the head), the head is broad and rounded at the apex, with a protractile mouth which lower lip is thin with a central cleft, and four barbels (circular section) which are closer to the tip of the snout than they are to the mouth. The series of longitudinal scutes are five: dorsal (1 series, 10–14 scutes), lateral (2 series, one per side, 30–42 scutes each) and ventral series (2 series, one per side, 8–11 scutes each). [5] The dorsal fin has no spines and 36 to 48 soft rays, and the anal fin has 24 to 31 soft rays. The dorsal colouring is olive-brown, the flanks are paler and the underside white. [6] [7] Juveniles have a flattened and triangular rostrum, with a distinctive colouring on the back, dark brown with wide paler areas casually distributed.
Adriatic sturgeon was reported as very similar to the critically endangered European sea sturgeon ( Acipenser sturio ), once sympatric in the Adriatic sea, but distinctive characters for A. naccarii are: [8]
The Adriatic sturgeon can be found in freshwater and marine environments, including estuaries and brackish water. Historically it was to be found in the Adriatic Sea and the rivers flowing into it on either side. In 1932 its range in the sea was reported to be from Venice and Trieste to Greece and Corfu. It used to be present in the rivers Adige, Brenta, Bacchiglione, Piave, Livenza and Tagliamento. In the Po and its tributaries, it used to be present as far upstream as Turin, and it was reported numerous in the Ticino and Adda rivers. It traditionally occurred along the Albanian coasts, and in the rivers of Slovenia, Croatia, Bosnia-Herzegovina and Montenegro, including Lake Skadar.[ citation needed ]
Once considered an anadromous species, a recent study affirms that A. naccarii is an euryhaline species facultatively migratory, which lives also into the sea but spends most of its life in the lower part of the rivers. [9] In the same study it has been reported that, unlike most of the species of sturgeons, A. naccarii is a facultative anadromous, since a small, isolated and structured population was spawning and maintaining above Isola Serafini Dam before the building of a fish ladder (on 2017, EU project Life11nat/IT/000188), at the mouth of Ticino river in the Po, without any migration to the sea; [10] [11] the distribution of the catches of this sturgeon throughout the year confirm this hypothesis. [12] This was never confirmed for the obliged anadromous A. sturio and Huso huso , other two species of sturgeon which once lived simpatrically with A. naccarii.[ citation needed ]
Adriatic sturgeons are slow-growing, long-lived fish; wild males are sexually mature at 7–11 years old (about 80 cm (2.6 ft), long), and females at 12–14 years old (at least 1 m (3.3 ft), long). Females ovulate every 2–4 years. [13]
During spring months mature fish migrate to the upper part of the rivers, then they lay eggs from April to June [14] in deep and oxygenated waters, on gravelly substrates at a depth of 2–10 m (10–30 ft), [15] with a current velocity of 0.8 m/s (2.6 ft/s) at least. [16] Water turbulence is very important for the reproductive success of sturgeons, since it avoids egg stress, aggregation of the eggs, anoxia, parasites, and predators. [17]
The eggs adhere at the substrate and hatch after about a week, fry are about 8–10 mm (0.31–0.39 in) long with pelagic attitude like other sturgeons, then after ten days they begin to be demersal. [8]
Adriatic sturgeons tend toward an opportunistic feeding, swallowing substrate together with prey and organic matter, including small decaying carrions. In the rivers they mainly eat gammarids, diptera larvae and oligochaetes, sometimes small fish, [18] which they suck up with their toothless, funnel-like mouths; considering the present invasion in the Po and other rivers of the allochthonous Corbicula sp., probably these freshwater clams are now an important prey. In the sea they eat gammarids, shrimps, crabs, demersal fish, molluscs (cephalopods, gastropods, bivalves) and vegetal matter. [19] In both cases, the analysis of the digestive tract revealed a high presence of inorganic matter (sand, silt, mud, etc., even plastic) mixed with food.
The typical habitat of A. naccarii are large, deep rivers with strong current, which flows in the Adriatic sea, mainly in its north-western portion. In the sea it lives in lagoons and close to the estuaries, mainly on muddy and sandy substrates, at a depth of 10–40 m (30–130 ft).
Juveniles of Adriatic sturgeon can adapt at a salinity of 20–30‰, [20] as opposed to other species of sturgeons. [21] However, despite some A. naccarii have been captured in the Adriatic Sea, it has been shown that this sturgeon tolerates with difficulty high salinity for extended periods, spending short periodsin marine environments for foraging activities. [22] The low tolerance to full-strength salt water constitutes a strong constraint to migration across Adriatic Sea where the salt contents can reach up to 37‰. [23] Furthermore, it has been shown, tracking the movements of tagged fish in some cold and oxygenated rivers of northern Italy (Piave, Sile, Livenza), that A. naccarii regularly moves to areas where the salt intrusion from the sea involves an electrical conductivity of 1000–4000 μS in the water (about 0.6–2.5‰ salinity at 18 °C (64 °F)), on equal terms of other environmental variables. [24]
A study on genetic variability of Acipenser naccarii, based on mitochondrial and nuclear DNA, showed that sturgeons of the Po basin are genetically distinguished from those of the Buna (Bojana) basin. So, the introduction of sturgeons of the Po in the Buna river would jeopardize the genetic differences between both populations and should thus be avoided [23] (if the Buna population is still existing).
The International Union for Conservation of Nature (IUCN) rates the conservation status of this fish as "critically endangered". For a long time, scientists reported that no spawning was observed in the wild. [1] However, a number of organisations are concerned in attempts to preserve this species and a captive breeding scheme has been established, with young microchipped fish released into the wild [1] officially since 2004, following EU projects (Life03nat/IT/000113 and subsequents); before 2004, almost only post-larvae and very small sturgeons were released (since 1988), at a time when fishing of sturgeons was still allowed in Italy (until 1997) and the allochthonous wels catfish (Silurus glanis) was at the apex of its numerical expansion in Italian rivers, so the survival rate was extremely low. [24] The captive broodstock for the programme of reintroduction comprised initially about 50 [8] individual fish. The Adriatic sturgeon is a tetraploid fish (has four sets of chromosomes) and research based on mitochondrial and microsatellite information is applied on the breeding stock to establish how best to increase the genetic diversity of the fish used in the breeding programme. [25] [26]
It has been reported by researchers that, despite the release of captive-bred fish, no signs of spawning have been observed in the wild; [1] however, considering that Adriatic sturgeon needs at least twelve years to attain sexual maturity and matures gonads in alternate years, and considering the release of captive small fish started in 2004, it was probably premature to look for wild fingerlings at the time of the publication of the report (2011).
About the southwestern population, it was reported that Adriatic sturgeon was seen for the last time in Greece in 1977, and in Albania in 1997 in the Buna River, but has not been seen there since; [1] however, in 2003 a study published genetic data of several specimens especially caught in Buna river, below the confluence with Lake Skadar. [23]
In the recent past catfish anglers caught, filmed and released mature specimens of Adriatic sturgeon in the Po and other rivers, also very large, old fish (for example, , ,). [27] After the building of a fish ladder on Isola Serafini dam, on 2018 a project GRAIA (Gestione Ricerca Ambientale Ittica Acque) started and a camera is now monitoring continuously the passage of fish through the mentioned ladder. Among millions of fish, mature specimens of Adriatic sturgeon were filmed.[ citation needed ]
The capture of juveniles without microchips, smaller than those released into the wild by researchers and authorities, is an indication that Adriatic sturgeon naturally spawned in Italian rivers. [28] Molecular analyses showed that, among those fish, some were not related with the captive broodstock, [8] so it seems that a wild broodstock still exists.
The main threat that Adriatic sturgeons face is damming, which involves the fragmentation of the habitat and prevents trophic and spawning migrations. The building of a dam severely modifies the river habitat upstream and downstream for many kilometers: upstream the current can be very slow, with water turbidity, water stratification and hypoxia or even anoxia on the bottom; downstream the nature of the substrate can change and water can be warmer and hypoxic, so the reproductive success of sturgeons can be very low or null and the metabolism of juveniles can be very stressed (above 23–25 °C (73–77 °F) for A. naccarii). [29] Before the building of some fish ladders on the main watercourses, most (if any) of the traditional spawning areas of the Po basin were not available to Adriatic sturgeons for decades, and this involved the collapse of wild populations of A. naccarii, as well as of other species of sturgeon (A. sturio, Huso huso ) in the Adriatic sea. The only suitable remaining habitat for spawning were in the vicinity of the confluence of the River Po with some of its tributaries. [1]
Another important problem is pollution of rivers by industrial effluent, agricultural runoff and civil wastewaters.[ citation needed ]
During the 20th century, overfishing on adults and above all immature sturgeons was another important cause of the decline of the wild stock of A. naccarii. Despite it is now a protected species, illegal fishing by poachers is presently one of the main threat in the Po basin (for example, ,), particularly harmful when smaller fish are taken before they have reached maturity and reproduced at least once. Illegal capture with giant lift nets placed close to the estuaries can be a big threat, as well as commercial fishing in the sea and lagoons.[ citation needed ]
Predation by Great cormorants on juveniles is another important problem: Italian wintering populations of these birds are extremely numerous and increasing every year, [30] so many of them are moving to rivers and lakes, due to numerical saturation of the coastal areas. [31]
Adriatic sturgeons also face competition from the wels catfish, which has expanded its range into Western Europe; however, wels catfish cohabits with many species of sturgeon in its native range. It has been supposed that, as they have become fewer in number, they could be affected by the Allee effect, [1] which postulates that a fish's growth rate is reduced at low population densities; however, any study was published about Allee effect on A. naccarii.
Sturgeon is the common name for the 28 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 (Polyodontidae). The family is grouped into four genera: Acipenser, Huso, Scaphirhynchus, 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 Africa.
The beluga, also known as the beluga sturgeon or great sturgeon, is a species of anadromous fish in the sturgeon family (Acipenseridae) of the order Acipenseriformes. It is found primarily in the Caspian and Black Sea basins, and formerly in the Adriatic Sea. Based on maximum size, it is the third-most-massive living species of bony fish. Heavily fished for the female's valuable roe, known as beluga caviar, wild populations have been greatly reduced by overfishing and poaching, leading IUCN to classify the species as critically endangered.
The kaluga, also known as the river beluga, is a large predatory sturgeon found in the Amur River basin from Russia to China and near Hokkaido in Japan. With a maximum size of at least 1,000 kg (2,205 lb) and 5.6 m (18 ft), the kaluga is one of the biggest of the sturgeon family. Like the slightly larger beluga, it spends part of its life in salt water. Unlike the beluga, this fish has 5 major rows of dermal scutes and feeds on salmon and other fish in the Amur with its nail like teeth in its jaws. They have gray-green to black backs with a yellowish green-white underbelly.
Acipenser is a genus of sturgeons. With 17 living species, it is the largest genus in the order Acipenseriformes. The genus is paraphyletic, containing all sturgeons that do not belong to Huso, Scaphirhynchus, or Pseudoscaphirhynchus, with many species more closely related to the other three genera than they are to other species of Acipenser. They are native to freshwater and estuarine systems of Eurasia and North America, and most species are threatened. Several species also known to enter near-shore marine environments in the Atlantic, Arctic and Pacific oceans.
The Chinese sturgeon is a critically endangered member of the family Acipenseridae in the order Acipenseriformes. Historically, this anadromous fish was found in China, Japan, and the Korean Peninsula, but it has been extirpated from Korea, Japan, and most regions in China due to habitat loss and overfishing.
The European sea sturgeon, also known as the Atlantic sturgeon or common sturgeon, is a species of sturgeon native to Europe. It was formerly abundant, being found in coastal habitats all over Europe. Most specifically, they reach the Black and Baltic Sea. It is anadromous and breeds in rivers. It is currently a critically endangered species. Although the name Baltic sturgeon sometimes has been used, it has now been established that sturgeon of the Baltic region are A. oxyrinchus, a species otherwise restricted to the Atlantic coast of North America.
White sturgeon is a species of sturgeon in the family Acipenseridae of the order Acipenseriformes. They are an anadromous (migratory) fish species ranging in the Eastern Pacific; from the Gulf of Alaska to Monterey, California. However, some are landlocked in the Columbia River Drainage, Montana, and Lake Shasta in California, with reported sightings in northern Baja California, Mexico.
The Atlantic sturgeon is a member of the family Acipenseridae, and, along with other sturgeon, it is sometimes considered a living fossil. The Atlantic sturgeon is one of two subspecies of A. oxyrinchus, the other being the Gulf sturgeon. The main range of the Atlantic sturgeon is in eastern North America, extending from New Brunswick, Canada, to the eastern coast of Florida, United States. A disjunct population occurs in the Baltic region of Europe. The Atlantic sturgeon was in great abundance when the first European settlers came to North America, but has since declined due to overfishing, water pollution, and habitat impediments such as dams. It is considered threatened, endangered, and even locally extinct in many of its original habitats. The fish can reach 60 years of age, 15 ft (4.6 m) in length and over 800 lb (360 kg) in weight.
The shovelnose sturgeon is the smallest species of freshwater sturgeon native to North America. It is often called hackleback, sand sturgeon, or switchtail. Switchtail refers to the long filament found on the upper lobe of the caudal fin. Shovelnose sturgeon are the most abundant sturgeon found in the Missouri River and Mississippi River systems, and were formerly a commercially fished sturgeon in the United States of America. In 2010, they were listed as threatened under the U.S. Endangered Species Act due to their resemblance to the endangered pallid sturgeon, with which shovelnose sturgeon are sympatric.
The sterlet is a relatively small species of sturgeon from Eurasia native to large rivers that flow into the Black Sea, Azov Sea, and Caspian Sea, as well as rivers in Siberia as far east as Yenisei. Populations migrating between fresh and salt water (anadromous) have been extirpated. It is also known as the sterlet sturgeon.
The starry sturgeon, also known as the stellate sturgeon or sevruga, is a species of sturgeon. It is native to the Black, Azov, Caspian and Aegean sea basins, but it has been extirpated from the last and it is predicted that the remaining natural population will follow soon due to overfishing.
The shortnose sturgeon is a small and endangered species of North American sturgeon. The earliest remains of the species are from the Late Cretaceous Period, over 70 million years ago. Shortnose sturgeons are long-lived and slow to sexually mature. Most sturgeons are anadromous bottom-feeders, which means they migrate upstream to spawn but spend most of their lives feeding in rivers, deltas and estuaries. The shortnose sturgeon is often mistaken as a juvenile Atlantic sturgeon because of its small size. Prior to 1973, U.S. commercial fishing records did not differentiate between the two species: both were reported as "common sturgeon", although it is believed based on sizes that the bulk of the catch was Atlantic sturgeon. The shortnose is distinguishable from the Atlantic sturgeon due to its shorter and rounder head.
The green sturgeon is a species of sturgeon native to the northern Pacific Ocean, from China and Russia to Canada and the United States.
The Persian sturgeon is a species of fish in the family Acipenseridae. It is found in the Caspian Sea and to a lesser extent the Black Sea and ascends certain rivers to spawn, mainly the Volga, Kura, Araks and Ural Rivers. It is heavily fished for its flesh and its roe and is limited in its up-river migrations by damming of the rivers. Young fish feed on small invertebrates, graduating to larger prey such as crabs and fish as they grow. The threats faced by this fish include excessive fishing with the removal of immature fish before they have bred, damming of the rivers, loss of spawning areas and water pollution. The International Union for Conservation of Nature has listed the fish as critically endangered and has suggested that the increased provision of hatcheries could be of benefit.
The Siberian sturgeon is a species of sturgeon in the family Acipenseridae. It is most present in all of the major Siberian river basins that drain northward into the Kara, Laptev and East Siberian Seas, including the Ob, Yenisei Lena, and Kolyma Rivers. It was also found in Kazakhstan and China in the Irtysh River, a major tributary of the Ob, though wild populations are extirpated in China. The species epithet honors the German Russian biologist Karl Ernst von Baer.
Dabry's sturgeon, also known as the Yangtze sturgeon, Changjiang sturgeon and river sturgeon, is a species of fish in the sturgeon family, Acipenseridae. It is endemic to China and today restricted to the Yangtze River basin, but was also recorded from the Yellow River basin in the past. It was a food fish of commercial importance. Its populations declined drastically, and since 1988, it was designated an endangered species on the Chinese Red List in Category I and commercial harvest was banned. It has been officially declared extinct in the wild by the IUCN as of July 21, 2022.
The Russian sturgeon, also known as the diamond sturgeon or Danube sturgeon, is a species of fish in the family Acipenseridae. It is found in Azerbaijan, Bulgaria, Georgia, Iran, Kazakhstan, Romania, Russia, Turkey, Turkmenistan, and Ukraine. It is also found in the Caspian Sea. This fish can grow up to about 235 cm (93 in) and weigh 115 kg (254 lb). Russian sturgeon mature and reproduce slowly, making them highly vulnerable to fishing. It is distinguished from other Acipenser species by its short snout with a rounded tip as well as its lower lip which is interrupted at its center.
Acipenser oxyrinchus is a species of sturgeon.
Huso is a genus of large sturgeons from Eurasia. It contains two species, both of which are critically endangered:
The Japanese sturgeon or Amur sturgeon is a species of fish in the family Acipenseridae found in the Amur River basin in China and Russia. Claims of its presence in the Sea of Japan need confirmation. The species has 11–16 dorsal, 34–47 lateral, and 7–16 ventral scutes. Their dorsal fins have 38–53 rays and 20–35 anal fin rays. They also have greyish-brown backs and pale ventral sides. The species can reach up to 3 metres (9.8 ft) in length, and weigh over 190 kilograms (420 lb). The species is considered to be critically endangered.
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