White salmon

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White salmon
Stenodus nelma.jpg

White salmon ( Stenodus leucichthys )

Systematics
Cohort : Euteleosteomorpha
Order : Salmonid fish (Salmoniformes)
Family : Salmon fish (Salmonidae)
Subfamily : Coregoninae
Genre : Stenodus
Type : White salmon
Scientific name
Stenodus leucichthys
( Güldenstädt , 1772)

The white salmon ( Stenodus leucichthys ) is an important pale- and nearctic food fish from the genus Stenodus in the family of salmon fish (Salmonidae). It is the largest member of the subfamily Coregoninae and feeds mainly predatory ( piscivor ), while the other species of the subfamily feed on plankton and benthalen invertebrates . It can be 1.5 m long, weigh 40 kg and be around 22 years old. In Russia it was also called the tsar or angelfish.

features

The pointed head takes up almost 1/5 of the total length. The upper mouth is larger than that of the related genera Coregonus and Prosopium (maxillary and supramaxillary are elongated). It extends to the level of the pupil. Very small but distinct teeth stand (“tight”, hence Stenodus , “narrow teeth”) on the jaws (maxillary: only at the upper end), the palatine (in ligaments), the vomer and the glossohyal (each a small group). Old animals have largely lost their teeth and no longer need them to snap. As with all Coregoninae, the color is light silver with a slightly darker, olive-green to gray-blue back. The dorsal and caudal fin have dark edges, the other fins are light.

The skull is medioparietal, i.e. H. the parietals meet median - but below them an extension of the supraoccipital always extends to the frontalia (see Boulenger 1895). There is a narrow supraorbital. The dentalia form a small hook or button at the front that fits into a pit in the premaxilla and is helpful when packing the prey. The fish has about ten gill skin rays on each side . The reus thorns are bony, fairly pointed and partly finely toothed; on the first gill arch there are 5–7 and 13–17 (with their narrowing the young fish can still catch nauplius larvae if necessary ). Stenodus has 64–69 vertebrae. The trunk is slightly flattened laterally.

The dorsal fin is high, pointed and shorter, but the anal fin is slightly longer than that of Coregonus . There is a distinct axillary process at the base of the pelvic fins. A somewhat elongated ventral lobe is sometimes noticeable on the caudal fin, which (like the position of the mouth) suggests that Stenodus (also) hunts near the surface.

In contrast to the related genera, the tail skeleton shows a pair of Urodermalia (Kendall and Behnke 1984). The scales are quite small (about 88–118 along the full side line ). At the exit of the S-shaped stomach there is an asymmetrical pair of tufts of pyloric tubes (approx. 100 to over 200).

Development and ecology

After hatching in late spring, the larvae (11–13 mm long) need their yolk sac for about two more weeks before they start to eat (harpacticids and other small crustaceans, chironomid and other insect larvae). As soon as they are able to do so, however, they switch to eating fish (e.g. eggs and larvae) - from then on they behave quite "wild, voracious", so that Albert Günther uses the now invalid name Luciotrutta for the genus , that is, “pike trout” .

The target of the anadromous specimens is the sea (in which, of course, they rarely move very far from the estuaries; down to a depth of 50 m and at temperatures below 18 ° C) - but there are also resident populations in the entire range that ("voluntarily" or thanks to insurmountable barriers ) stay in fresh water (in lakes - for example in the Great Slave Lake - or rivers). After several years (a minimum of five [males] up to a maximum of fifteen [females]) they then rise again into the rivers in autumn to spawn, although they usually do not penetrate high into the mountains or into the source rivers like the real salmon; Rapids and waterfalls do not entice them to overcome. Nevertheless, the ascent can take months (e.g. even more than a year earlier in the Volga ); it partly happens under ice.

Many questions about the biology of the various populations remain to be clarified. The food intake is apparently stopped during the train. At the spawning site, the males and the slightly larger females behave like other Salmoniformes, but the eggs are not buried, but ejected and inseminated in the open water - they then sink to the bottom and stick to gravel and the like. Spawning takes place at water temperatures below 6 ° C (usually September, October). Large females can easily shed 500,000 eggs in several batches per season. The spawned fish only die in small numbers, but return to their habitat - they can join the migration five times (but probably not every year) and more often. In contrast to Oncorhynchus , for example, they hardly contribute to the nutrition of their young. The egg development lasts for months until the arctic spring.

Stenodus accepts that stronger floods destroy a lot of spawn and brood, but in spring, on the other hand, the number of predators is still low and later the nutritional situation for the young fish is more favorable (than for spring spawners - which incidentally occurs in the subspecies leucichthys in the Volga lower reaches also gave or gives). Some waters are “dominated” by the Njelma as the sole top predator; after strong Oncorhynchus ascents, whose salmon larvae and young fish serve as food, their population can often develop very well. As a predatory Coregone, it can compete with salmon, burbot or pikeperch. The food of fish older than 2+ consists practically exclusively in all manageable fish, e.g. As in the Caspian Sea, especially in Gobiiden and clupeids, otherwise also coregonids, smelt, Dallia and young salmon. Occasionally, however, it is noted that Njelmy is caught, whose stomach is filled with small mussels (Finsch 1879).

Subspecies and (former) distribution

As usual with the Coregoninae, there are still taxonomic ambiguities with this genus. Usually Stenodus is considered monotypical ; However, some authors want to give the " race " ( leucichthys ) of the catchment area of ​​the Caspian Sea species status: they (the "white fish", Russian белорыбица / belorybiza ) have a shorter head compared to the northern European-Siberian "race" ( nelma , Njelma , нельма ), which is also identical to the North American one (initially described by Richardson in 1823 as mackenzii ; Nearctic vernacular names are whitefish, she (e) fish ("woman fish"), l'inconnu ("the unknown" - hence also "Conny" ) and "sii", more precisely siiriroaq (among others among the Eskimos ) and others. Stenodus easily forms all kinds of hybrids with Coregonus spp. and Prosopium spp. in the breeding stations.

Stenodus leucichthys nelma occurs in many rivers and streams of Siberia , whose watersheds extend to China. The Njelma is also known from northern European rivers (eastwards from the White Sea ), but (despite expectations) not from Scandinavia. In the Nearctic, it is restricted to the northwest ( Alaska , Yukon and parts of the Northwestern Territories of Canada to the Anderson River ; especially in the Yukon and Mackenzie areas ) and the offshore sections of the Arctic Ocean. It also lives in the North Pacific or its tributaries such as the Anadyr and some rivers in northern British Columbia.

Since the Ice Age, the Bjelorybitsa, i.e. the nominate subspecies, S. leucichthys leucichthys , has been an endemic to the Caspian Sea and its largest tributary, the Volga (in which it could migrate very far upwards due to the low gradient; were particularly important as spawning rivers but their tributaries Ufa and Belaja ), further the Ural river , while Terek and Kura were hardly inhabited (however, it is also given as 'indigenous' to Turkey, which should refer to the Kura as a tributary). Even on the Persian south coast of the sea, the Bjelorybitsa is not entirely unknown, although it can only be fished from the cool deep regions here in summer. In Central Asia (up to Mongolia) local populations were settled in several reservoirs.

use

When the Europeans became aware of this fish from Siberia and North America , the descriptions of the travelers (e.g. in Brehms Tierleben , Vol. 8 (3rd edition 1892, pp. 349–352)) gave the impression of inexhaustible schools. The gold rush on the Yukon at the turn of the 19th and 20th centuries was largely sustained in nutritional terms by the tasty and invigorating oily meat of the Inconnu. We now know that huge flocks of large fish particularly easy in the Arctic due to temperature-induced low productivity überfischbar are. They could just serve the local Eskimos, Indians, Samoyed etc. for subsistence . But later measures of river regulation and energy generation had an even more drastic effect on the populations. The Bjelorybitsa is now extinct as a wild form (especially due to the Volga dams, which prevented spawning migration) and practically only exists in fish-farming populations. These are, however, interspersed with nelma genetics in a way that is no longer completely transparent , which is particularly true of the Kazakh, Turkmen etc. populations.

Of the Anadyr population (among the Chukchi ), only the freshwater portions in the upper reaches exist because of the large dams. In North America, the situation is a little better because major “river expansions” are only being planned there. "Ascent aids" ( fish ladders ) would hardly be accepted by the Inconnu (in contrast to salmon). At the moment the "Connie" can only handle sport fishermen. The export (especially smoked, less frozen) is necessarily low - there are hardly any “production figures”.

There are also still uncertainties regarding health concerns about fish from waters with tributaries from (former) heavy metal mines. It has been found that so-called heat shock proteins (HSP), which act as markers for exposure to mercury and the like. a. were valid and are easier to quantify than the metals themselves, so that they are much less reliably correlated than previously assumed.

Individual evidence

  1. ^ SA Stephenson, Jeff A. Burrows, John A. Babaluk: Long-Distance Migrations by Inconnu (Stenodus leucichthys) in the Mackenzie River System. (PDF; 475 kB) In: ARCTIC. 58 (1), 2005, pp. 21-25, doi : 10.14430 / arctic385 .
  2. ↑ a b Stenodus leucichthys on Fishbase.org (English)
  3. ↑ Marine Species Identification Portal: Güldenstadt's whitefish (Stenodus leucichthys). In: species-identification.org. Retrieved January 20, 2015 .

Web links

Commons : White Salmon ( Stenodus )  - Collection of images, videos and audio files