Data from: Cleaner fish escape salmon farms and hybridize with local wrasse populations

The genetic impact of farmed fish escaping aquaculture is a highly debated
issue. However, non-target species, such as cleaner fish used to remove
sea lice from farmed fish, are rarely considered. Here we report that wild
corkwing wrasse (Symphodus melops), which are transported long distances
to be used as cleaner fish in salmon farms, escape and hybridize with
local populations. Recently, increasing numbers of corkwing wrasse have
been reported in Flatanger in Norway, north of its described distribution
range, an area heavily relying on import of cleaner fish from Skagerrak.
Using genetic markers identified with 2bRAD sequencing, we show that,
although the Flatanger population largely is a result of a northwards
range expansion, there is also evidence of considerable gene flow from
southern populations in Skagerrak and Kattegat. Out of 40 corkwing wrasses
sampled in Flatanger, we discovered two individuals with clear southern
genotypes, one first generation hybrid, and twelve potential
second-generation hybrids. In summary, we provide evidence that corkwing
wrasse escape from fish farms and hybridize with local populations at the
leading edge of an ongoing range expansion. Although the magnitude and
significance of escapees warrants further investigation, these results
should be taken in consideration in the use of translocated cleaner fish.