Mountain stream in the context of Weißbach (Lattengebirge)

⭐ Core Definition: Mountain stream

A mountain stream is a brook or stream, usually with a steep gradient, flowing down a mountainside. Its swift flow rate often transports large quantities of rock, gravel, soil, wood or even entire logs with the stream. The main characteristic of mountain streams in the Alpine region is their steep gradient and sharply varying rates of flow within a short period of time, as a result of snowmelt and sudden storms. Streams of such nature are rarer in gently rolling countryside, although they may occur on scarp slopes where, although the height difference is not so great, they tend to have a larger catchment area than mountain streams.

Mountain streams may be broadly divided into three sections. In the "catchment funnel" (Sammeltrichter) high on the mountainsides, water and eroded soil, rock and gravel are gathered. The stream then flows at high speed through a "drainage channel" (Abflussrinne) into the "alluvial fan" where the transported debris is deposited.

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Mountain stream in the context of Ray-finned fish

Actinopterygii (/ˌæktɪnɒptəˈrɪdʒiaɪ/ ; from Ancient Greek ἀκτίς (aktís) 'ray, beam' and πτέρυξ (ptérux) 'wing, fins'), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that constitute nearly 99% of the over 30,000 living species of fish. The vast majority of extant actinopterygian species are teleosts, and by species count they dominate the subphylum Vertebrata, comprising over 50% of all living vertebrates. They are the most abundant nektonic aquatic animals and are ubiquitous throughout freshwater, brackish and marine environments from the deep sea to subterranean waters to the highest mountain streams. Extant species can range in size from Paedocypris, at 8 mm (0.3 in), to the giant sunfish, at 2,700 kg (6,000 lb), and the giant oarfish, at 8 m (26 ft) (or possibly 11 m (36 ft)). The largest ever known ray-finned fish, the extinct Leedsichthys from the Jurassic, is estimated to have grown to 16.5 m (54 ft).

Ray-finned fish are so called because of their lightly built fins made of webbings of skin supported by radially extended thin bony spines called lepidotrichia, as opposed to the bulkier, fleshy fins of the sister clade Sarcopterygii (lobe-finned fish). Resembling folding fans, the actinopterygian fins can easily change shape, orientation and wetted area, providing superior thrust-to-weight ratios per movement compared to sarcopterygian and chondrichthyian fins. The fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the articulation between these fins and the internal skeleton (e.g., pelvic and pectoral girdles).

View the full Wikipedia page for Ray-finned fish

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