Migratory fish are fish that change their habitat to spawn . Fish that stay in the same habitat for their entire life are called stationary .
The fish migration primarily serves to find food or suitable breeding grounds for the animals. For example, many fish follow seasonal plankton clouds through the oceans. The migration to the spawning waters can be justified by the different needs of the young fish and the adult animals.
Migratory fish are divided into:
diadromous species ( Greek διά diá "through" and δρομάς dromás "running") as a generic term for species that alternate between fresh and salt water. Fall under
- anadromous migratory fish (Greek ἀνά aná "up"), for example the salmon that swims up the river from the sea to spawn
- katadromous migratory fish (Greek κατά katá "down"), for example the eel that swims downstream into the sea to spawn there
- amphidromous migratory fish (Greek ἀμφί amphi "on both sides") that migrate regularly between sea and fresh water or vice versa, without these migrations serving for reproduction
- potamodrome species (Greek ποταμός potamós "river") that only migrate in fresh water.
Most marine fish spend spawning in the marine regions they live in or migrate to other marine areas. However, some species migrate from the sea into the freshwater and lay their eggs there in suitable spawning grounds. These fish migrate back into the sea when they are young and benefit from the richer food sources. The egg-laying but can not take place in the sea, because the eggs and the fry other environmental claims have (gravel bed, fresh water, food).
The u. a. The sea trout ( Salmo trutta trutta ) occurring in Germany and the salmon migrate back to the very waters in which they were born. In doing so, they follow their sense of smell and their memory of the smell of their home waters. However, many species only make this journey once in a lifetime. When they arrive at the spawning grounds, they are usually completely exhausted and have lost around 40% of their body weight. In contrast to the semelparen Pacific salmon ( Oncorhynchus spp. ), However, a small part of the European salmon ( Salmo salar ) survives the spawning migration, while the majority of the sea trout survives , so they are strictly speaking iteroparous .
While salmon and sea trout spend most of their lives in sea water and migrate up the rivers to spawn, the opposite is true for eels . They mostly live in fresh water and often visit spawning grounds thousands of kilometers from their home river.
The migration of the eels was a mystery for centuries. They suddenly appeared as young eels at the mouths of the rivers and swam into the upper reaches, stayed there and then returned to the sea as fully grown animals. However, through long-term studies with acoustic and radio transmitters , the European eels were finally followed to their spawning grounds in the Sargasso Sea . Here the eels spawn and then die. Leaf-shaped larvae hatch from the eggs and drift eastward with the current, reaching the coasts of Europe and penetrating the rivers. American eels spawn in the Sargasso Sea as well as in the North Pacific, and the numerous species of eels in Southeast Asia in the Indo-Pacific.
Species that regularly migrate between sea and freshwater are called amphidromes when these migrations are not for reproduction. Reasons for these migrations are food acquisition or wintering. Like the bull shark , which looks for food in sea water as well as in fresh water and swims far up inland and has even been spotted in fresh water lakes.
- Hiroshi Ueda, Katsumi Tsukamoto [Eds.]: Physiology and Ecology of Fish Migration. CRC Press, 2014. ISBN 978-1-4665-9514-9
- Matthias Schaefer: Dictionary of Ecology. Spektrum Akademischer Verlag, 2011, ISBN 978-3827425614 , p. 13.
- A. Zitek, G. Haidvogl, M. Jungwirth, P. Pavlas, S. Schmutz: An ecological-strategic guide to restoring the continuity of running waters for the fish fauna in Austria , AP 5 of the MIRR project, final report. Study on behalf of the Ministry of Life and the Province of Lower Austria. 2007. p. 16 ( online ; PDF; 3.7 MB).
- Migratory fish (German)