Cobitis 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 : 129

Cobitis spp (spined loach)

Two species of spined loach ( Cobitis ) are often considered to be native around the central Alps: Cobitis bilineata is native to the Po river catchment, while C. taenia has a wide geographic range north of the Alps [9]. In Switzerland, the spined loach of the northern perialpine and midland region was often assumed to be C. taenia (Fish atlas), but Kottelat & Freyhof reported C. bilineata as introduced to northwstern Switzerland [9]. All Cobitis recorded by Projet Lac phenotypically resembled C. bilineata ( Figure 41 ). This included those in the northern perialpine lakes Neuchatel, Morat and Biel (excluding one distinct phenotype in Lake Biel, see below), and all lakes south of the Alps that had Cobitis (Como, Mezzola, Iseo, Garda, Maggiore and Varese) . Similarly, all Cobitis recorded by Progetto Fiumi on both sides of the Alps resembled C. bilineata . Among other distinguishing features, C. bilineata has two black spots on the base of the tail and C. taenia has only one spot on the upper section of the tail. The identity of Projet Lac and Progetto Fiumi samples as C. bilineata was confirmed by DNA barcoding, which revealed identical barcodes in the fish analysed from north and south of the Alps, consistent with reason range expansion.Thus, no C. taenia were recorded in Swiss lakes and rivers north of the Alps and it is unclear whether C. taenia ever occurred in the northern perialpine region, or whether C. bilineata has recently invaded and displaced a putatively native species. We inspected Cobitis samples from the Lake Biel region from the 1930s in the Natural History Museum of Bern. Many of these fish were so strongly bleached that their melanin pattern was reduced to invisibility, but the few that could be identified were clearly C. bilineata . In this regard it is also important to note, that C. taenia seems absent from the entire upper Rhone catchment in France northwest of Switzerland [149] and has only isolated occurrences in southwestern Germany (Baden Württemberg south of Karlsruhe), mostly confined to the Rhine valley. Populations from the Seine catchment (Yonne, Figure 41 ) and the Karlsruhe region are very clearly C. taenia [150].

[9]

Cobitis species are often diagnosed based on distinctive features in the shape and arrangement of melanic blotches and stripes. Among our samples from Lake Biel was one fish with a pattern very different from C. bilineata and C. taenia ( Figure 41 ). Instead of dark blotches that are squared or longer than high, and separated by gaps about as wide or wider than the blotch itself, this fish had blotches that were higher than long and were separated by gaps clearly narrower than the blotch. It also had more vertical lines of black spots on the caudal fish than most C. bilineata . It seems most likely that this fish is a deviant phenotype of C. bilineata but it could be a different species, especially since the taxonomy of the Cobitis in eastern Europe is very poorly resolved. More samples will be needed from Lake Biel to answer this question.

Figures

Figure 41: All Cobitis caught in Projet Lac in lakes north and south of the Alps resembled Cobitis bilineata, except one fish from Lake Biel that was phenotypically distinct from C. bilineata and also from C. taenia (fishec number 168747). Photo of C. taenia from the Yonne river (Seine, France) is provided for comparison (photo from Guy Periat).