The Italian nase (Chondrostoma soetta)

Geographic Distribution

Chondrostoma soetta, or the Italian nase, and it is present in almost all of northern Italy. The Italian nase is also found in some artificial lakes Tuscan-Emilian Apennines and Lazio, after repopulation carried out for the benefit of sport fishing.

 Habitat

The Italian nase inhabits lower reaches of main rivers with moderate current, in deep water, over gravel bottom and in oligo-mesotrophic lake. It performs significant shifts both in the lake water as in fluvial environments, reaching close to the coast only during the warm season (Grimaldi in Manzoni, 1990). It moves in the middle and upper sections of the rivers and into smaller watercourses during the breeding season.

 Biology

The Italian nase is a gregarious fish of medium size (maximum total length is about 40 cm and weight of 900 g), presumably active throughout the year. The knowledge of its biology is in some aspects deficient, and this does not allow to establish effective interventions to preserve the species. The maximum age observed in the wild is 11 years. Growth is rather slow: at three years, the length is 13-15 cm, at five years is 22-26 cm. The females have a faster growth of males, but only starting from 5 years of age. The specimens of larger size are predominantly females, possibly because males have a lower survival rate.

From the trophic point of view the Italian nase can be defined as "grazing" on the bottom, thanks to a particular morphological adaptation: the mouth is in position infera and lower lip with thick cornified sheath.

The plant component is always clearly prevalent in the diet, with percentages ranging from 60 to 95% of the food consumed, and consists of epilithic algae, macrophytes, and occasionally parts of plants of riparian vegetation. Together with the plant it gobbles up also zoobenthic elements, especially gastropod molluscs. The age at which sexual maturity is reached appears to be variable, in relation to the speed of growth. In the fluvial environment have been observed mature specimens of both sexes at the age of three years (14 cm in total length). There is no sexual dimorphism.

The breeding occurs in April and May, with a migration within the hydrographic basins. In the lakes and in the lower and middle sections of the rivers, they congregate in groups of hundreds of individuals, then go up the river,  the tributaries and the small affluents too. The deposition of gametes occurs in fresh waters and currents, with gravelly bottoms near the shore. The females lay about 100,000 eggs with a diameter of 1.5 mm (Grimaldi and Manzoni, 1990). Observations made on the breeding sites identified into watercourses tributary of Lake Maggiore and Lake Lugano, have allowed a detailed description: depth that ranges from 0.1 and one meter, water velocity, measured at 5 cm from the bottom, 0, 3 to 1.1 m / s, temperature 10.4 to 17.1 ° C; substrates deposition of gametes predominantly gravelly, but occasionally consist of aquatic vegetation, sand and rocks.

 Conservation Status

The Italian nase is one of the inland water fish species that has undergone the most damage by the construction of dams and other barrages along the rivers. These artifacts hinder the free movement into watercourses, required to achieve appropriate areas for care. Even the artificiality of the beds in the middle and upper sections of rivers and the withdrawals of gravel in the river bed, represent real threats to the species, as they reduce the spawning grounds.

In Friuli-Venezia Giulia the populations are in sharp decline for the competition with Chondrostoma nasus, non-native species introduced in the 60s in the Slovenian part of the Isonzo basin and spread throughout the basin.

To ensure the performance of the biological cycle of the populations of Chondrostoma soetta, and thus their survival, it’s possible identify the following measures: construction of fish passes in correspondence with the dams, protection of spawning areas and prevent the introduction of alien species.

 

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