Contaminants reach everywhere: Fish dietary samples should be surface decontaminated prior to molecular diet analysis.

Knowledge of trophic interaction is necessary to understand the dynamics of ecosystems and develop ecosystem-based management. The key data to measure these interactions should come from large-scale diet analyses with good taxonomic resolution. To that end, molecular methods that analyze prey DNA from guts and feces provide high-resolution dietary taxonomic data. However, molecular diet analysis may also produce unreliable results if the samples are contaminated by external sources of DNA. Employing the freshwater European whitefish (Coregonus lavaretus) as a tracer for sample contamination, we studied the possible route of whitefish in beaked redfish (Sebastes mentella) guts sampled in the Barents Sea. We used whitefish-specific COI primers for diagnostic analysis, and fish-specific 12S and metazoa-specific COI primers for metabarcoding analyses of intestine and stomach contents of fish samples that were either not cleaned, water cleaned, or bleach cleaned after being in contact with whitefish. Both the diagnostic and COI metabarcoding revealed clear positive effects of cleaning samples as whitefish were detected in significantly higher numbers of uncleaned samples compared to water or bleach-cleaned samples. Stomachs were more susceptible to contamination than intestines and bleach cleaning reduced the frequency of whitefish contamination. Also, the metabarcoding approach detected significantly more reads of whitefish in the stomach than in intestine samples. The diagnostic analysis and COI metabarcoding detected contaminants in a higher and comparable number of gut samples than the 12S-based approach. Our study underlines thus the importance of surface decontamination of aquatic samples to obtain reliable diet information from molecular data.

Gyrodactylus triglopsi n. sp. (Monogenea: Gyrodactylidae) from the Gills of Triglops nybelini Jensen, 1944 (Teleostei: Cottidae) in the Barents Sea.

INTRODUCTION: Monogeneans of the genus Gyrodactylus were found on the gills of specimens of the bigeye sculpin Triglops nybelini Jensen, 1944 caught by trawl in the Barents Sea in January-February 2016. METHODS: Morphological preparations of the parasites were examined and photographed under a microscope at magnifications of × 100-1000 and morphometric analyses were carried out on 22 specimens using ImageJ2 software. Eight of the specimens used for the morphological comparisons were also subjected to molecular analyses by sequencing a region of the ribosomal DNA spanning partial 18S, the internal transcribed spacers 1 and 2 (ITS1 and 2), 5.8S and partial 28S and comparing this with other species through a BlastN-search in GenBank and through phylogenetic analyses. RESULTS: The morphology of the species from T. nybelini was markedly different to that of any of other species of Gyrodactylus. It is characterized by having relatively long hamulus roots, a character that it shares with two other species described from marine sculpins (Cottidae); G. armatus and G. maculosi. It also has a narrow rectangular ventral bar membrane with a posterior notch which it shares with G. maculosi only. Compared with all the seven species from marine Cottidae described so far, it has the smallest opisthaptoral hard parts. A comparison of the internal transcribed spacer (ITS) rDNA sequence with available sequences in GenBank and a phylogenetic analyses also showed it to be highly divergent from other sequences. Therefore, a new species is proposed, Gyrodactylus triglopsi n. sp. CONCLUSION: Both the morphological and molecular analyses support the status of G. triglopsi as a new species. This is to our knowledge the first species of Gyrodactylus described from Triglops nybelini and the description extends the list of Gyrodactylus species found on fish in the Barents Sea to 17.

Antlers and parasites.

Development of ornamental characters exposed to directional selection may be particularly sensitive to the effect of parasitic infections. Antlers are ornamental characters of importance in intraspecific interactions, and are in reindeer (Rangifer) developed by both males and females. By antihelmintic treatment of naturally infected female reindeer we show that parasite intensities affect development of antler asymmetry, but not antler length. These results suggest that asymmetry in antlers may reflect parasite intensities and thus be of importance in intraspecific assessment of genetic resistance towards infectious organisms.