Perca fluviatilis, Linnaeus, 1758

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 : 145

European perch

( Perca fluviatilis )

were recorded in all except the alpine lakes (Sils and Poschiavo) and was the most abundant species caught in Projet Lac. Across most of central Europe, P. fluviatilis typically have red fins and four to six vertical bars (some of which are often V-shaped). Perch populations in lakes across Switzerland exhibited unusually large variation in fin colour (common and extremes of fin coloration), as well as in the number of vertical bars within and among lakes. Most lakes were dominated by fish with yellow-orange or yellow fins, but highly distinct red-finned forms were found along with the yellow-finned forms in Lugano, St-Point, Geneva, Walen and Constance ( Figure 56 , Figure 57 ). Many Perca fluviatilis recorded in Projet Lac also exhibited unusually large variation in the vertical striping, ranging from four bars to eight or more.

In Lake Constance, yellow-finned perch with many vertical bars was the more common phenotype caught in Projet Lac, whereas red-finned fish with few vertical bars, resembling classical central European perch, were much rarer. DNA-barcoding of Constance perch as part of Projet Lac showed that yellow-orange finned perch were genetically distinct from red-finned fish. This corresponded with previous genetic analysis of perch in Lake Constance using microsatellite DNA, which also revealed significant genetic variation between yellow-finned and red-finned individuals [187]. The earlier study also showed that the yellow-finned perch were more vulnerable to infection by several parasites (tapeworm Triaenophorus nodulosus and gill worm Ancyrocephalus percae), which do not generally cause damage to the red-finned perch and populations elsewhere. The combination of the significant genetic differentiation and different immune responses between the red-finned and yellow-finned perch in Lake Constance suggest that these are two genetically distinct species with different evolutionary histories.

An additional level of genetic and taxonomic variation among perch in Switzerland is again best demonstrated by earlier work in Lake Constance.This work revealed strong genetic differentiation between the populations of Perca fluviatilis living in Lower and Upper parts of Lake Constance (Untersee and Obersee) [188]. The two populations most likely originate from different glacial refugia that met in Lake Constance during range expansion after the last glacial period, and persist as two distinct species with little hybridisation [189]. Experimental evidence suggests that divergence between the two populations may be maintained by postzygotic isolation through genetic incompatibility. It is not yet clear whether and how the variation and differentiation between fin colour types is related to this historical differentiation of lineages. Further work is needed to clarify the status and species diversity in Lake Constance perch.

[190]

Fin coloration was recorded for most perch collected in Projet Lac and lakes were determined to contain only the common yellow/orange-finned form, or both yellow/orange- and red-finned forms.The assignment as such is not meant to imply that yellow- and red-finned perch are distinct species in every lake. However, the phenotypic diversity in many lakes and in the region overall, is unusual compared to places elsewhere in Europe, and the situation requires careful genetic, ecological and phenotypic analysis. Until the situation is properly understood, a precautionary approach to conservation should treat red- and yellow-finned perch as two different management units. The likely outcome will be that red- and yellow-finned perch are distinct species in some lakes, but not in others.

Figures

Figure 56: Variation in morphology, banding and fin colour in Perca fluviatilis. Figure 2 from [186].

Figure 57: Extremes of variation in fin colour in Perca fluviatilis within and among lakes.