Mucous cell size and distribution were investigated in the skin of five salmon using a novel stereology-based methodology: one (48 cm) fish to test 15 tissue treatment combinations on measures of cell area and density on the dorsolateral region and, using the most suitable treatment, we mapped mucous cell differences between body regions on four (52 cm) salmon, comprising a male and a female on each of two diets. The section site, decalcification, embedding medium and plane of sectioning all impacted significantly on mucous cell size, whereas mucous cell density is more robust. There were highly significant differences in both mucosal density and mean mucous cell size depending on body site: the dorsolateral skin of the four salmon had significantly denser (about 8% of skin area) and larger (mean about 160 μm(2)) mucous cells, whereas the lowest mean density (about 4%) and smallest mean area (115 μm(2)) were found on the head. We found that 100 random measurements may be sufficient to distinguish differences >7 μm(2) in mean mucous cell areas. The results further suggest that salmon exhibit a dynamic repeatable pattern of mucous cell development influenced by sex, diet and possibly strain and season.

Karlson, S., Michalsen, K., and Folkvord, A. 2013. Age determination of Atlantic halibut (Hippoglossus hippoglossus L.) along the coast of Norway: status and improvements. – ICES Journal of Marine Science, 70:50–55. This study re-evaluates the current ageing methodology for the Atlantic halibut, Hippoglossus hippoglossus. The traditional method is through surface readings of otoliths, but, based on new experiments with different preparation treatments and techniques, a more accurate and cost-efficient procedure for the age determination of Atlantic halibut is proposed.

The Nansen Legacy Polar Cod Connectivity cruise aimed at unravelling polar cod and capelin population connectivity and relation to the physical and chemical environment in Svalbard’s fjords. The main focus areas were Isfjorden, Kongsfjorden, Storfjorden and the South-East of Svalbard. A total of 36 stations were visited to collect of information on polar cod and capelin vertical and horizontal distribution (using echosounder, pelagic and bottom trawls), their population, life cycle and size structure (observation of maturity, otoliths reading and genetic sampling), as well as their diet (stomachs content, sampling of benthic/planktonic prey). Other studies were conducted in link with the objectives of the research foci RF2 The Human Impacts and RF3 The Living Barents Sea. The cruise was also an opportunity to visit well-known monitoring stations to complete already long time series and investigate seasonal variability.  The cruise started November 12th in Longyearbyen and ended in Tromsø on November 22nd, 2022. The first two days and a half were spent on multidisciplinary sampling in thirteen stations distributed in contrasted areas inside Isfjorden. A rockhopper gear strapping was installed after the first bottom trawl to avoid mud and rocks and kept for the whole cruise. There were some difficulties also with the grab which did not always close. It was possible to spend one day sampling Kongsfjorden, thanks to relatively good weather and low sea-ice conditions. However, the presence of cables on the seafloor and irregular and unsuitable bottom types in that fjord did not allow for bottom trawling to sample demersal and benthic communities. After approximately one day of steaming south in good weather conditions, the sampling continued in Storfjorden. However, the shallowest stations north of Storfjorden and on the way out of the fjord towards the South-East of the archipelago could not be sampled due to time constraints and difficult navigational access. Finally, five multidisciplinary stations could be sampled in the South-East of Svalbard before the two-days transit to Tromsø. Overall, most stations were visited. Polar cod largest fish were maturing, but not mature. Further analyses of the samples should unveil potential genetic differences across the fjords, and image analyses of plankton net samples will be able to detect if there were already eggs in the water column at the beginning of the dark season. There was very little signal on the echosounder during most of the cruise, but the extractive sampling revealed a diversity of communities in the different fjords.