Parasites as biological tags for cod, Gadus morhua L., in northern Norway: a pilot study

Abstract

The purpose of this study was to investigate the feasibility of using parasites to separate stocks of cod in northern Norway. Three samples of cod, totalling 103 fish, were taken from three locations: one in the southern Barents Sea and one each from Balsfjord and Ullsfjord. Sixteen species of parasite were found, seven of which showed statistically significant differences in prevalence of infection between locations. The large difference between the Balsfjord and Barents Sea samples provides evidence that cod in Balsfjord may comprise a population separate from those in Ullsfjord and the Barents Sea. Several parasite species were selected as potentially useful biological tags. The most promising, mainly because of their long life spans (> 1 year) in fish hosts, are the protozoan Myxidium sp. (from the gall bladder), and the larval nematodes Pseudoterranova decipiens and Phocascaris sp. The digenean Hemiurus levinseni and the acanthocephalan Echinorhynchus gadi probably have life spans of less than 1 year but could be useful for tracing seasonal migrations of cod. Two other protozoans that could not be detected in the deep frozen cod examined in this study are considered to be potentially useful tags provided fresh material is available.