European river zonation

This zone has a characteristic steep gradient, fast flowing water and cool temperature. The fast flow rate causes turbulence which keeps the water well oxygenated. Fish species found in this zone usually lay adhesive eggs that can stick to the substrate, this is to help prevent eggs being carried down stream by the water flow.

Characteristic fish species are:

• Brown trout (Salmo trutta)
• Atlantic salmon (Salmo salar)
• Bullhead (Cottus gobio)
• Loach (Barbatula barbatula)

Similar in physical characteristics to the Trout zone, although the temperature is usually slightly higher. Fish species in this zone also lay adhesive eggs.

Characteristic fish species include all of the above species, with the addition of;

• Grayling (Thymallus thymallus)
• Minnow (Phoxinus phoxinus)
• Chub (Leuciscus cephalus)
• Dace (Leuciscus leuciscus)

This zone is essentially lowland, but retains some characteristics of upland rivers. It has a gentle gradient with a moderate water flow and temperature. It also has a good oxygen content and a mixed substrate of silt and gravel in which plants can take root. Most of the fish species found in this zone lay their eggs in the vegetation on the river bed, this provides them with good protection and allows the eggs a good supply of oxygen given off from photosynthesis in the plants.

Characteristic fish species include all of the species from the previous zones with addition of;

• Barbel (Barbus barbus)
• Roach (Rutilus rutilus)
• Rudd ( Scardinius erythrophthalmus )
• Perca ( Perca fluviatilis )
• Lucio ( Esox lucius )
• Anguila ( Anguilla anguilla )

La verdadera zona de tierras bajas presenta una pendiente muy suave y aguas de corriente lenta. Generalmente, el contenido de oxígeno es bueno, pero la temperatura es mucho más variable que en las demás zonas. Esta zona tiene un sustrato limoso y suele ser turbia . Las especies de peces que se encuentran en esta zona depositan huevos adhesivos en las algas. La mayoría de las especies de peces de tierras altas no pueden sobrevivir en esta zona.

Las especies de peces características incluyen solo unas pocas especies de la zona del barbo (rutilo, bermejuela, perca y lucio), con la adición de:

• Dorada ( Abramis brama )
• Tenca ( Tinca tinca )
• Carpa ( Cyprinus carpio )