Total lipid content, and lipid and fatty acid composition of the deep-water prawn Pandalus borealis from Balsfjord, northern Norway: growth and feeding relationships

Variations in total lipid content (g of lipid, and as % of wet and dry body weights) of the prawn Pandalus borealis, ranging from eggs to 52 mo old adults, indicate that lipid growth exhibits marked seasonal oscillations while growth in carapace length shows only comparatively weak seasonality. Positive (anabolic) lipid growth occurs from about April to September inclusive (with up to 40 % of dry body weight as lipid), the major production season for both phytoplankton and herbivorous zooplankton. Negative (catabolic) lipid growth (with lipid being reduced to about 10 % of dry weight) is prominent during the winter. Correspondence analysis involving the relative body-content of total lipid, total protein, ash and water indicates that both 'age' and 'seasonally' related trends are visible; lipid tends to play an increasingly important rôle with age but lipid levels oscillate between peaks in late summer (August/September) and troughs in late winter (February/March). Qualitative investigations of gut contents and analyses of lipid-class composition and fatty acid food-chain markers of selected sizes and ages of prawn indicate that lipid-rich zooplankton (mainly copepods and krill) form the bulk of the food of prawns from 1 to 4 yr old. Although benthic polychaetes and detrital material tend to increase in relative importance with increasing size and age of prawn, they are of secondary importance compared to pelagic organisms. The older prawns frequently contained substantial numbers of capelin scales, probably from feeding on discarded fish from prawn trawling. This study thus reveals that P. borealis in north Norwegian fjords is linked trophically to the highly seasonal pelagic production cycle. The lipid percentage of P. borealis is, however, less than that of herbivorous zooplankton but substantially greater than that of the lipid-deficient benthos.