Hazel ( Leuciscus leuciscus )
|( Linnaeus , 1758)|
The hazel ( Leuciscus leuciscus , Greek λευκός, leukós “shiny, shining, white”) is a small-stature representative of the carp fish . It is of very little economic importance in Europe and is easily mistaken for other members of its family because of its typical " white fish " shape.
distribution and habitat
The hazel predominantly inhabits deep flowing waters from the trout to the barbel region in Europe , Siberia and Kazakhstan . It can also be found in rivers and reservoirs, and more rarely in stagnant waters. He prefers to stay in clear water areas, mainly in calming zones or slowly flowing sections. In Germany, the hazel can be found in the entire federal territory, with the population density decreasing from south to north. In Austria the species is also widespread and in Switzerland it can be found in larger bodies of water in the catchment area of the Rhine. Isolated populations in Swiss mountain lakes can probably be traced back to escaped or released bait fish.
The spindle-shaped and slightly flattened body of the hazel rarely reaches a total length of more than 25 centimeters. The crack in the mouth is small, only slightly beveled and a little below. It does not reach the edge of the eye and is slightly surmounted by the muzzle. The outer edge of the dorsal and anal fin is concave, the caudal fin is clearly notched. On the back, the hazel is bluish-greenish or steel blue in color, the sides and the belly have a silvery sheen or are yellowish-white. The pectoral and pelvic fins are light gray to yellowish in color and occasionally show a reddish tinge, which is less intense than, for example, in the chub ( Leuciscus cephalus ). The dorsal and anal fins are gray to gray-green.
Outside the spawning season, the hazel shows no obvious sexual dimorphism, only the pectoral and ventral fins are slightly longer in males. During the reproductive period, the males develop a fine-grained spawning rash that extends over the forehead, the sides of the body to the abdomen. The pearl organs are also found on the pectoral fins and to a lesser extent on the pelvic fins.
The number of medium-sized scales along the sideline is relatively variable. In most cases it ranges between 47 and 52, but varies between 45 and 55 overall. The most common pharyngeal tooth formula is 2.5-5.2 or 2.5-5.3.
Way of life
The shy and very fast swimmer is a sociable schooling fish. Its food spectrum is broad; the hazel feeds mainly on invertebrates or larvae and algae that live in the water. He also takes on approach food and occasionally higher water plants or seeds from bank plants. The search for food takes place in all water layers and fluctuates over the course of the day, irregular phases of breaks and eating alternate. The time of the most intensive food intake is usually the twilight hours.
Hazel spawn between March and April at water temperatures below ten degrees Celsius. Before the spawning season begins, they undertake short hikes upstream. Below suitable spawning grounds, the fish gather in deeper and quieter areas and stay there until they reproduce. The spawning area itself is typically very shallow and with a lot of currents, with water depths of significantly less than 50 centimeters. Accordingly, the ground and bank area are stony and there are hardly any taller plants. Spawning usually takes place at night. The eggs released into the water immediately become very sticky when they come into contact with water. They are quickly distributed over the entire spawning area by the current and usually stick under large stones. Because of this scattering, hazel eggs are usually found singly on the substrate and rarely in small clumps. The size of the gray-white and relatively opaque eggs varies depending on the length of the female between 1.3 and 2.5 millimeters, with an average diameter of two millimeters. After about 260 degrees the larvae hatch; with a length of seven to eight millimeters, they are significantly larger than the larvae of other carp fish living in Europe . Before the yolk sac is completely consumed, the offspring begin to eat. In the beginning, rotifers and diatoms are mainly eaten, as well as small green algae , ciliates and flagellates . The larval phase ends after about eight weeks. The fry then have reached a size of about three centimeters. They usually reach sexual maturity in their fourth year of life. The average life expectancy of the hazel is ten years, under optimal conditions a maximum age of up to 16 years is possible.
- Otfried Wüstemann, Bernd Kammerad: The hazel . Westarp Sciences, Magdeburg 1995, ISBN 3-89432-447-3 .