The range of distribution of Barbus plebejus is restricted to the Po river basin (including the southern part of Switzerland), all river basins in northern Italy, the Soca-Isonzo river basin (Slovenia-Italy), Reba basin, the Dragonia River, and in Croatian rivers as far as Krka river. It also occurs in lakes. The southern boundary on the Adriatic coast of Italy can not be established with certainty, because this species is one of those most subject to sowing and introductions. Tuscany and Lazio in the district, especially in the basins of the rivers Arno, Ombrone, the Tevere and is certain his presence in the past. In our country still represents a sub endemism.
The barbel is a long-lived reofilo species which inhabits running waters of the hill and lowland zones of rivers (Huet, 1949, Baras and Cherry, 1990), although it is characterized by discrete ecological valence: it is therefore able to occupy various stretches of a river, however, preferring gravel or sandy substrate and rivers with moderately deep, well oxygenated flowing water on foothill regions.
In the ontogeny is evident, however, a marked variation in habitat use: there are differences in the use of microhabitats within the first year of growth: the species of size> 1 + prefer relatively fast and deep waters beyond the state of smaller size (Watkins et al., 1997). Juvenile fish are still able to use both lotic habitats both lentic (Copp et al., 1994; Baras et al., 1995, Watkins et al., 1997), using the vegetation as a refuge from the floods and predation (Power, 1987; Copp, 1992).
The flow rate of the river body is directly proportional to the larvae drifting downstream (Copp et al., 2002): this phenomenon ensures the dispersal of populations to the valley, maximizing the fitness (Jonsson, 1991; Copp et al., 2002). The presence of gravelly substrate is important for the reproduction. The specimens of larger size are used to colonize areas downstream of the spawning beds, showing the ability to tolerate a certain turbidity of the water and live well even in environments with moderate speed of water. Populations of small claims are also present in oligotrophic lakes.
The barbel is a gregarious fish, size medium-large who live in small groups, preferably in the sections where the water is deeper. It has benthic habits, especially for trophic reasons. The diet consists mainly of macro-invertebrates such as insect larvae and crustaceans, gastropods and occasionally macrophytes. The increase is similar in both sexes but the survival of females is higher. The males, which constitute 33-40% of the population in the third year of age, gradually decrease and eventually disappear with age classes 6 + and 7 +.
Searches carried out on growth in the river Po have revealed that the LT to 1 year is 14-20 cm and 20-100 g of weight, to 3 is 32-34 cm and 450-500 g of weight, to 5 is 41-42cm and 950-1050 g and to 7 years (females only) reach 70 cm to about 3200 g. Sexual maturity is reached at 2-3 years and 4-5 years in males and females. There is no obvious sexual dimorphism. The deposition is generally single event (Baras, 1993). Reproduction takes place when the water temperature reaches 16-17 ° C, and then between April and July depending on the location. During the breeding season the barbs back the waterways making real migration of tens of kilometers until you find areas with gravelly bottom current and lively: barbel show high fidelity to a breeding site over the years (Hancock et al. 1976; Baras, 1995b).
In the breeding season males reach the spawning beds before females (Lucas and Batley, 1996), in order to maximize the number of fertilized females (Hancock et al. 1976). The deposition tends to persist over time, the eggs are relatively large (2:37 to 1.95 mm) and preferentially laid on the gravel ( Kryzhanovsky , 1949) at different depths. The eggs hatch after 8 days at 16 ° C.
The species is extremely vagile : studies in England confirm the trend of the barb to go upstream during the reproductive period and migrate downstream in the autumnal period, especially in conjunction with flood events ( Lucas and Frear , 1997). Despite the vagility studies confirm a strong homing ( Baras , 1996; Lucas and Batley, 1996; Ovidio et al. , 2007), leading to define the species as " stationary and vagile " (Hunt and Jones , 1974; Penaz et al. , 2002). Summarizing the results obtained in some European rivers (Hunt and Jones, 1974; Pelz and Kastle , 1989; Baras and Philippart , 1989; Baras and Cherry , 1990; Baras , 1997), it can be concluded that the barb has an annual home range of about thirty Km
The Barbus plebejus is a species relatively resistant. It can tolerate moderate degradation of water quality: it can be defined as species euriecia. However, the alterations of the environmental characteristics and modification of the substrate necessary for the reproduction can lead to a sharp contraction of populations. An important role in the decrease of the species in our waters seems, at present, the spread of one or more exotic species of Barbus (Barbus spp.), for trophica competition and hybridization. The species, as litofila it needs to achieve specific reproductive substrate. This need, which is also confirmed in a morphology suited to swimming, is often denied due to the presence of artificial barriers such as dams or dams. The fragmentation of river habitats seems to strongly affect the vitality of European populations.