Phoxinus

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 : 128

In the Alpine region, the large phenotypic variation of Phoxinus in lakes Sils and Poschiavo was tentatively interpreted in the field as indicating the presence of two species, assumed to correspond to P. lumaireul and P. phoxinus [148] before the genetic work. However, barcoding revealed that the two species were actually P. septimaniae and P. csikii , with both species occurring in both lakes (the only native species likely being P. csikii in Sils). Underwater observations in Lake Poschiavo revealed that shoals dominated by one species occurred in close proximity to shoals dominated by the other species, with some mixed shoals in the very shallow littoral zone.

Regarding the physical appearance of the minnow species, Phoxinus csikii of the Aare lakes appear to be phenotypically distinct from P. septimaniae and P. lumaireul . P. csikii is smaller, more slender, with a less blunt head, more silvery and less yellow colouration, has more and smaller blotches along the midlateral line and very dark, metallic, green-black male coloration. Males and females of P. septimaniae often appear deep yellow, both with very yellow fins.The few large males of P. lumaireul obtained in Lake Garda also appeared yellow ( Figure 40 ). Future work is needed to investigate the ecological relevance of phenotypic differences between the Phoxinus species , determine the extent of distribution range overlap between them and to quantify possible gene flow and morphological and ecological differences between these species and their ecological interactions where they co-occur within a lake / stream system. Further work should also investigate the identity of the many minnow populations in smaller alpine lakes that were not sampled in Projet Lac or Progetto Fiumi.

Figures

Figure 40: The three different Phoxinus species recorded in Projet Lac. P. septimaniae from lakes Chalain and Poschiavo. P. csikii from lakes Thun, Lucerne, Walen. P. lumaireul from Lake Garda.