Marbled trout

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Marbled trout
Pure Salmo Marmoratus.jpg

Marbled trout ( Salmo marmoratus )

Systematics
Overcohort : Clupeocephala
Cohort : Euteleosteomorpha
Order : Salmonid fish (Salmoniformes)
Family : Salmon fish (Salmonidae)
Genre : Salmo
Type : Marbled trout
Scientific name
Salmo marmoratus
( Cuvier , 1829)
Distribution area of ​​the marbled trout

The Marbled trout or marble trout ( Salmo marmoratus ) is a living in fresh water, large-growing trout ( Salmo ). It belongs to the family of salmon fish ( Salmonidae ). It occurs in large rivers and tributaries that drain into the northern Adriatic . Because of its eponymous pattern, it can be distinguished from other types of trout. The marbled trout can live for over 10 years and reach a body length of 1.20 meters. The largest female specimen found dead weighed 24 kg, but there have been reports of catches up to 30 kg.

morphology

The marbled trout has a torpedo-shaped body that is flattened on the side and therefore only forms a small area of ​​attack for the current. It has strong fins, the caudal fin is not indented. She wears small scales. The color spectrum ranges from gray, green to brown and depends on the respective body of water. The marbling is only clearly visible at the age of about two years. The pattern covers the entire body except for the fins. Due to the lack of red dots, one can distinguish the marbled trout from the brown trout and hybrid forms . Her head looks beefy and the gap in the mouth extends behind the eye. Both mouth and tongue are covered with strong teeth, which indicates a predatory lifestyle.

distribution and habitat

The natural range of the marbled trout is limited to a few tributaries of the Adriatic . It extends from Croatia to Slovenia to northern Italy . Typical waters in which the marbled trout occur are the Soča and Rižana in Slovenia and the Passer and Adige in South Tyrol . Due to stocking and spawning migration , the marbled trout can sometimes even be found in mountain streams. As it grows, however, it looks for deep sections of the river, where deep gullies and pools offer it the necessary protection. It prefers cool, oxygen-rich waters, in which summer temperatures do not exceed 15 ° C. Gravelly stretches of water that offer a suitable spawning bed must be available as the substrate .

Reproduction

The females are usually sexually mature after about four years, the males one year earlier. At the beginning of the spawning season , which lasts from late October to December, the marbled trout migrate upstream to their spawning grounds. The form cock fish from spawning typical features, such as an intense coloration and the formation of spawning hook . When the fish have reached a suitable place, the Rogner begins to knock out a spawning pit. The tail fin and the tail stalk are tapped on the gravel until the smaller substrate piles up behind it. A pit is created at the knocking point, in which there is less current than in the surrounding area. The male territorial at that time defends the mature female from competitors , so the strongest animal usually comes into play. After the eggs have been laid in a bed of gravel with a depth of 0.6 to 0.8 meters, they are fertilized by the milkman and covered with gravel by the rogner. The average number of eggs is 1,500 to 2,000 per kilogram of body weight and can be divided into several spawning pits . Then the trout can be drifted downstream again and look for their old resting places. In the past, large marbled trout migrated back to the brackish water , where they stayed for several months to feed. Due to construction, the hiking routes are blocked today and a decrease in size is observed. The brood hatches after 45 days. After 59 to 63 days, the fry are feeding on a variety of invertebrates. The adult fish are fish-eaters.

nutrition

The food spectrum of the marbled trout depends on its age, size and habitat. Young fish mostly eat drifting food such as macrozoobenthos . They mainly include stoneflies , caddis flies and mayfly larvae . In the warm seasons, their adults are also taken from the surface. As the size of the marbled trout increases, its protein needs increase and it becomes significantly more predatory. The small Mühlkoppe or bullhead is the main prey in many waters, but cannibalism is also frequently observed.

Hazard and protection

The marbled trout is listed by the IUCN as "critically endangered" in the main distribution area in northern Italy and as "not endangered" in the entire distribution area. The causes of danger include:

  • The hybridization with the brown trout : In many bodies of water only hybrids are found that can be recognized by the marbling in combination with the clearly defined red dots.
  • Heavy construction: Bank straightening and canalization of rivers destroy shelters in many cases and lead to habitat loss .
  • Rising energy pressure: The massive expansion of hydropower in recent decades has created several problems for the marbled trout and other river dwellers. On the one hand, there is no water that is not in the river between discharge and re-discharge. Furthermore, dammings represent an ecological barrier which migratory fish can only overcome with difficulty, even with the help of fish ladders . Periodic flushing of reservoirs leads to fish mortality and spawning area sludge.
  • Increasing fishing intensity.
  • Excessive stocks of allochthonous fish species such as rainbow trout and char .

The marbled trout is listed by the European Union in Appendix II of the Habitats Directive and is therefore considered a species of community interest, for whose conservation special protected areas must be designated by the member states.

literature

  • The marbled trout - queen of South Tyrol's fish . State Fisheries Association of South Tyrol, 2008.
  • JL Bagliniere, G Maisse: Biology and Ecology of Brown Sea Trout . Springer Verlag, Berlin 2007, ISBN 1-85233-117-8 .
  • R. Gerstmeier, T. Romig: The freshwater fish of Europe . Kosmos Verlag, 1998, ISBN 3-440-07068-9 .
  • Maurice Kottelat : European Freshwater fishes. An heuristic checklist of the freshwater fishes of Europe (exclusive of former USSR), with an introduction for non-systematists and comments on nomenclature and conservation (= Biologia. Vol. 52, Supplement 5, ISSN  1335-6380 ). Slovac Academic Press, Bratislava 1997.
  • Maurice Kottelat, Jörg Freyhof : Handbook of European Freshwater Fishes. Kottelat, Cornol 2007, ISBN 978-2-8399-0298-4 .
  • http://www.iucn.it/scheda.php?id=-788860032

Web links

Commons : Marbled Trout ( Salmo marmoratus )  - Collection of images, videos and audio files

Individual evidence

  1. ↑ M. Kottelat, J. Freyhof: Handbook of European freshwater fishes . Publications Kottelat, Switzerland 2007, p. 646 .
  2. ↑ L. Pintar: Najtežja soška postrv je končala pod peskom. In: Ribič. Vol. 50, No. 1/2, 1991, ZDB -ID 419429-9 , p. 16.
  3. ↑ Meta Povž, Dusan Jesenšek, Patrick Berrebi, Alain J. Crivelli: The marble trout, Salmo trutta marmoratus, Cuvier 1817. In the Soca River basin, Slovenia. Tour du Valat, Arles 1996, ISBN 2-910368-16-5 .
  4. ↑ M. Povz: Status of the freshwater fishes in the Adriatic catchment of Slovenia . 72nd edition. Biol. Conserv., 1995, pp. 171-177 .