Two species of pike in the genus Esox are considered native to Switzerland. The northern pike Esox lucius is widespread in cooler fresh and brackish water across the northern hemisphere.The second species Esox cisalpinus was described from lakes south of the Alps in 2011 based on genetic and phenotypic evidence [152, 153]. It was described under two different names by two author teams in the same year, with the name E. cisalpinus considered to have precedence over E. flaviae. The formal description suggested that adult E. lucius exhibit only the round-spotted phenotype, while E. cisalpinus shows mostly diagonal bars or stellate spots, with some fish showing vertical or horizontal bars. The number of scales along the lateral line also seems to distinguish the two species, with E. cisalpinus ranging from 101 – 115 scales and E. lucius generally from 125 – 148 scales [153]. Figure 43 shows the phenotypic variability of Esox caught in Projet Lac. Indeed, all very large E. lucius (> 60 cm) exhibited the round-spotted pattern. Intermediate-sized adults were more variable, for example the fish from Lake Walen with stripes and spots arranged in diagonal bars. Multiple round-spotted phenotypes, matchingEsox lucius, were also recorded in Projet Lac in some southern lakes (Maggiore and Lugano), corresponding with previous reports of the northern species in these lakes as a result of stocking [153]. Among the DNA-barcoded Esox from the southern lakes, one fish from Lugano was genetically identified as E. lucius (corresponding with its northern phenotype; Figure 43). All other pike from the southern lakes were E. cisalpinus in their mitochondrial sequence (5 from Lugano, 3 from Maggiore, 3 from Garda, 1 from Como, 1 from Mezzola), despite some having the northern, round-spot pattern (Figure 43). Interbreeding between E. cisalpinus and stocked E. lucius may have caused this disconnection between phenotype and mitochondrial genotype (barcode).
[153]
Considerable genetic divergence emerged among the barcoded E. lucius from the northern lakes, between the fish of the western lakes of the sampled region (Chalain, Annecy) compared to other northern lakes. Despite evidence suggesting the additional presence of E. cisalpinus in Lake Geneva in the first half of the 19 th century (barcoding of historic samples from a museum collection) [154], all ten Esox barcoded from Lake Geneva in Projet Lac were genetically E. lucius. Two lineages were apparent among the Geneva pike however, with five of the fish sharing the lineage of a historically sampled E. lucius (also collected in the first half of the 19 th century) [154] 4. This lineage was also shared with two pike from Lake Joux.The five other E. lucius from Lake Geneva shared a lineage with fish of other northern perialpine lakes (including also one fish from Lake Joux). Another distinct lineage of E. lucius contained all barcoded pike from Chalain (3 fish) and one from Annecy. This lineage clustered with GenBank reference samples mostly from Canada (as well as other parts of Europe) and may reflect the translocation of fish for stocking.