The Danube roach (Rutilus pigus)

Geographic Distribution

Rutilus pigus has been termed the Danube roach. It is native to northern Italy and Switzerland. It inhabits subalpine lakes of the Northern Adriatic basin, including Lakes Maggiore, Lugano and Como, and in the main left tributaries of the River Po: sublacuale Ticino, Adda, Serio, Oglio in Lombardy and Brenta, Livenza, Adige, Piave and Sile in the Veneto region. It is also found in the lakes of Mantua while it is almost absent in the Lake Garda. For more than a decade has been entered in some artificial lakes of the Tuscan-Emilian Apennines of Lazio.

 Habitat

The Danube roach is a species of freshwater and areas rich in vegetation. It Inhabits deep waters of large, subalpine lakes and large to medium sized rivers. Occurs in small groups.

It performs significant movements along the water column: during the summer it prefers surface waters, while with the arrival of winter it moved to considerable depth (Grimaldi and Manzoni, 1990). In large pre-alpine lakes mainly lives at depths of 10-15 meters, in winter it moves into deeper waters, it seems around 100 meters. In the spring moves at depths of 7-8 meters.

 Biology

The Danube roach is a fish of medium size (in Italian populations the maximum total length is about 45 cm and the weight reaches about 1.5 kg). With regard to the biology of Pigo little is known. It feeds on the bottom and the vegetable component in the diet prevails, in particular filamentous algae. There are benthic invertebrates too, especially snails and insect larvae. Lives up to 10 years or so (on the Ticino River were captured a few specimens that possessed a higher age: 11-12 years). Studies on the population of the Ticino River have shown that this species can reach the different ages of the following measures of length: 13 cm in the 1st year, 2nd year 20 cm, 32 cm in the 3rd year, 4th year at 36 cm , about 40 cm per year 5.

In the Ticino River has been observed a different trend growth for both sexes: females are characterized by slower growth and constant compared to males. The males appear to grow faster between five and eight years (Graia Ltd., 2004). In the population of Lake Como, where investigations were carried out on certain aspects of the life cycle, sexual maturity is reached at 3 years and 4 years in males and females. Studies on the reproductive biology of this species in the River Ticino have instead shown that while the majority of males will be played for the first time in four years of age, females become mature only five years. Sexual dimorphism is evident only during the breeding season, when males have a darker pigmentation nuptial tubercles on the head and eye-catching and spread in the dorsolateral region of the body.

The reproduction occurs in April-May, when the water temperature reaches 14 ° C or so. Each female produces an average of 50,000 eggs (for the population of the River Ticino returns a number between 17000 -35 000), through a series of successive depositions, which are exhausted in a few hours. In lacustrine environments sexually mature individuals will lead to deposition in shallow coastal waters with lithic substrates. In running waters the areas for the deposition are characterized by medium-low water (deep by 20-30 cm to about 1 m), with roundstone substrate (granulometry prevailing 10-15 cm), full transparency of the whole water column, speed current also strong. Can hybridize with the gardon (Graia Ltd., 2004).

 

 Conservation Status

in Italy the Danube roach populations are in sharp decline from several decades. One of the causes is surely represented by dams that prevent to the individuals mature to reach the depths suitable for reproduction. Another cause is the sport fishing carried out during the breeding season. In the lacustrine environments the species is subject to sport fishing in the most part of the year and in some cases, as in Lake Como, it is the subject of professional fishing.

To reverse the negative trend suggests: the regulation of fishing in a more restrictive manner by considering both the months in which the reproduction occurs (April and May) and a previous period. The construction of fish passes in correspondence with dams. Other factors that may have led to the decline of the Italian populations, you must also include the introduction of rutile, exotic species capable not only of hybridizing with the Danube roach but also to occupy the same trophic niche (Graia Ltd., 2004).

 

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