Rutilus spp

Alexander, Timothy & Seehausen, Ole, 2021, Diversity, distribution and community composition of fish in perialpine lakes – “ Projet Lac ” synthesis report, Eawag: Swiss Federal Institute of Aquatic Science and Technology : 120

Rutilus spp (roach and related species)

Three species of Rutilus were recorded by Projet Lac in the perialpine lakes: common roach ( Rutilus rutilus ) is native to the Rhine and Rhone catchments and most of Europe (excluding Italian and Iberian peninsulas and Mediterranean drainages of the Balkan peninsula), while triotto (R. aula) and pigo ( R. pigus ) are native and endemic to the northern Adriatic basin, mainly the Po catchment ( Figure 34 ). Rutilus rutilus was one of the most common species in Projet Lac, recorded in all northern perialpine lakes.This species was also recorded in a large number of fishing actions within each lake. Usually restricted to the littoral zone, R. rutilus also dominated the open water, pelagic zone of some smaller lakes: Remoray, Hallwil, Morat and Brenet. R. rutilus populations in the two most pristine oligotrophic lakes, Lake Brienz and Lake Walen, are genetically and – in the case of Lake Brienz – also phenotypically distinct from Rutilus in the other northern pre-alpine lakes [145]. Additionally, within Lake Brienz, fish from rocky boulder and cobble habitats are phenotypically distinct from those living over any other substrate type (; Figure 35 ). We consider these to be different roach populations of high conservation priority. That Rutilus from more heavily impacted lakes geographically as distant as Lakes Geneva, Neuchatel and Hallwill are genetically more similar to each other than to those from Lakes Brienz and Walen may imply that Rutilus populations have lost parts of their distinctiveness in the course of ecosystem perturbation and stock transfer. In several Rhine lakes we also recorded intergeneric hybrids between Rutilus rutilus and Abramis brama ( Figure 34 ).

Figures

Figure 34a: Rutilus species of the perialpine region. Rutilus aula (triotto) and Rutilus pigus (pigo) are native south of the Alps. Rutilus rutilus (roach) is native to the northern perialpine region and is introduced in many southern perialpine lakes, and invasive in several.

Figure 35: Rutilus rutilus population genomic structure across northern perialpine lakes and phenotypic structure within Lake Brienz.Top left: Principal component analysis based on 3,865 polymorphic Single Nucleodide Polymorphisms: black = Lake Brienz, orange = Lake Walen, red = Lake Hallwill, green = Lake Geneva, blue = Lake Neuchatel.Top right: RAxML phylogeny tree depicting the genetic relationship among the individuals from the five lakes. Bottom left: Morphological (Mahalanobis) distances between roach caught over different substrates within Lake Brienz [145]. Bottom right: representative individuals from the five lakes.