Browsing by Author "Faust, Ellika"

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Crossing barriers: Genetic consequences of translocating wild cleaner fish for aquaculture
(2022-04-21) Faust, Ellika
Several species of fish show a symbiotic cleaning behaviour, where they assist other species by feeding and removing dead skin or ectoparasites. Some of these cleaner fish species are used as a low-cost parasite control in salmon aquaculture, often considered to be more environmentally friendly than other delousing methods. Approximately 54 million cleaner fish are annually used in Norwegian salmon farms. This has resulted in an increasing fishing pressure on wild cleaner fish populations. Together with long-distance translocation, this raises concerns of potential overfishing, anthropogenic introductions, and hybridisation. Recently, increasing numbers of corkwing wrasse (Symphodus melops), have been reported in mid Norway, north of its described distribution range. This is an area heavily relying on the import and translocation of cleaner fish from Skagerrak-Kattegat, more than 1000 km away. Using genetic markers, I show that the new population is both a result of a northward range expansion, as well as a translocation of individuals from southern populations. Further investigation revealed that escapees and hybrids may constitute up to 20 % of the populations at the northern edge of the species distribution. In contrast, escapees and hybrids are rare in other parts along the Norwegian west coast, where salmon farming is also common. The set of genetic markers has a high power to detect escapees and hybrids, and can be applied to monitoring of wild populations. Investigations of corkwing wrasse in Skagerrak-Kattegat revealed reduced genetic diversity, a weak pattern of isolation by distance, and surprisingly little population structure. This suggests a very recent colonisation and high connectivity among sites in this region. Along the Swedish west coast, I evaluate the potential effects of the newly established wrasse fishery on local ecosystems and populations, and provide a baseline to support ecosystem-based management for wrasse fisheries in Sweden. I also investigate the genetic population structure of lumpfish (Cyclopterus lumpus) across the Atlantic, which is the most commonly used cleaner fish species. I show that there is a lot more structure than previously known, and identify eight genetically divergent regions. Hierarchical analysis of these regions demonstrates additional local and cryptic substructure. The genetic markers used her can also be applied for management of wild lumpfish populations and the identification of population origin. Overall, these findings provide important information both for aquaculture management and conservation of wild populations, and have implications for the increasing use and translocation of cleaner fish for parasite control in aquaculture. Moving genetic material between isolated populations could drastically alter the genetic composition and erode population structure, potentially resulting in loss of local adaptation and hampering natural range expansion. Although the ecological and evolutionary significance of escapees warrants further investigation, these results should be taken into consideration in the use of translocated cleaner fish.
Genetic Identification of Corkwing Wrasse Cleaner Fish Escaping from Norwegian Aquaculture
(University of Gothenburg / Göteborgs universitet, 2021) Faust, Ellika; Department of Marine Sciences / Institutionen för marina vetenskaper
The genetic impact of farmed fish escaping aquaculture is a highly debated issue. However, non-target species, such as cleaner fish that are used in fish farms to remove parasitic sea lice, 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 wrasse populations. Recently, increasing numbers of corkwing wrasse have been reported north of its described distribution range, in Flatanger in Trøndelag in Norway, an area heavily relying on the import of cleaner fish from Skagerrak. Using a high number of nuclear genetic markers identified with 2bRAD sequencing, we show that, although the Flatanger population is largely a result of a northward range expansion, there is also evidence of considerable gene flow from southern populations in Skagerrak. Of the 40 corkwing wrasses first sampled in Flatanger, we discovered two individuals with clear southern genotypes, one first-generation hybrid, and 12 potential second-generation hybrids. Thus, we found clear evidence of gene flow from source populations of translocated cleaner fish at the edge of an ongoing northwards range expansion. To better understand the extent of gene flow we then greatly expanded our sampling. Based on patterns of genetic divergence and homogeneity, we identified a smaller battery of 84 SNPs which is able to detect escapees with a Skagerrak origin as well as first and secondgeneration hybrids with high accuracy and power. We then used these SNPs to investigate the magnitude and geographic extent of escaping and hybridizing cleaner fish along the Norwegian coast. We found that escapees and hybrids may constitute up to 20 % of the local populations at the northern edge of the species distribution. In other parts of the Norwegian coast where salmon farming is also common, we found surprisingly few escapees and hybrids. Possible causes for few escapees and hybrids found in these areas are difficult to evaluate with the current lack of reporting of translocations by aquaculture operators. Overall, these findings provide critical information both for aquaculture management and conservation of wild populations of non-target species, and have implications for the increasing use of cleaner fish as parasite control in fish farms, that is both poorly documented and regulated. Moving genetic material between isolated populations could drastically alter the genetic composition and erode population structure, potentially resulting in loss of local adaptation and hampering natural range expansion. Although the ecological and evolutionary significance of escapees warrant further investigation, these results should be taken into consideration in the use of translocated cleaner fish.