The food of Galeus melastomus, Gadiculus argenteus thori, Trisopterus esmarkii, Rhinonemus cimbrius , and Glyptocephalus cynoglossus (Pisces) caught during the day with shrimp trawl in a West-Norwegian fjord

The stomach contents of the five species were analysed with respect to frequencies, average numbers, and average weights of the food taxa. The food of G. a. thori, which was studied thoroughly for the first time, was dominated by euphausiaceans (mostly by Meganyctiphanes norvegica) copepods, and mysidaceans. In each of the other four species, the most important groups of animals in the food were the same as those found in previous studies. In T. esmarkii, R. cimbrius, and G. cynoglossus a positive correlation was found between the optimal lengths of the fish with respect to the proportions (by number) of the numerically dominant food species, and the sizes of these food species. Information on the vertical ranges of the food species with the highest frequencies was used to deduce the relative positions of the horizontal zones used for feeding by the fish species. G. cynoglossus mostly took its food on the bottom, R. cimbrius just above the bottom, T. esmarkii on a higher level, and G. a. thori on the highest level. The feeding zone of G. melastomus was vertically wider than those of the other species and its mean level was somewhere between the levels of R. cimbrius and T. esmarkii. The number of different food species eaten by a fish species, the numerical toll taken of a food species by a fish species, and the nutritional utilization made of a food species by a fish species were determined largely by 1) the composition of the potential food of the fish species, which was in turn determined by the vertical range used for feeding by the fish species, and by 2) selection with respect to the size of the food species, other kinds of selection being considered less important.