Willy Hemmingsen

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.

The occurrence of some metazoan parasites of Atlantic cod, Gadus morhua L., in relation to age and sex of the host in Balsfjord (70°N), North Norway

Abstract Age and sex differences in the occurrence of some metazoan parasites were investigated in 243 cod (Gadus morhua L.) from Balsfjord, a subarctic fjord in northern Norway. Thirteen species of parasite were studied, comprising seven nematodes, three parasitic copepods, one acanthocephalan, one cestode and one digenean. The nematode Anisakis simplex showed significant increases in both prevalence and mean abundance with host age, while the digenean Hemiurus levinseni showed a significant increase in mean abundance with age. The increases probably result from a long parasite life-span for A. simplex and changes in the feeding pattern of cod with age for H. levinseni. Prevalence of the nematode Contracaecum sp. and mean abundance of the acanthocephalan Echinorhynchus gadi were significantly higher in male than in female cod, whereas mean abundance of H. levinseni was significantly higher in female cod. These results suggest that there may be differences in feeding behaviour between male and female cod in Balsfjord.

A population study of cod, Gadus morhua L., in northern Norway using otolith structure and parasite tags

Abstract A total of 502 cod, Gadus morhua L., was taken during spring and autumn sampling from three different localities in northern Norway: the Barents Sea, a silled fjord (Balsfjord) and an open fjord (Malangen). Each cod was allocated, according to its otolith structure, to one of two types, coastal or Arcto-Norwegian, and was then examined for infections of four species of parasite: the myxosporeans Myxidium oviforme and Zschokkella hildae , the digenean Hemiurus levinseni , and the copepod Lernaeocera branchialis . Both types of cod were present at each locality, with coastal cod dominating in the fjords in both seasons and in the Barents Sea in spring, but with Arcto-Norwegian cod dominating in the Barents Sea in autumn. Differences in the proportions of the two types of cod and in parasite prevalences between seasons and localities were interpreted as indicating a migration of coastal cod from the Barents Sea sampling area into the fjords between March and October. We found no evidence that Arcto-Norwegian cod from the Barents Sea migrate into the fjords, but our results suggest that the fjords contain local resident populations of Arcto-Norwegian cod. It is concluded that local parasite faunas are not greatly influenced by genetic differences between the two types of cod, but that their compositions are determined largely by variations in the abundance of intermediate hosts.

Migration of adult Elaphostrongylus rangiferi (Nematoda: Protostrongylidae) from the spinal subdural space to the muscles of reindeer (Rangifer tarandus).

To trace the intrahost migration of adult (fifth-stage) Elaphostrongylus rangiferi 9 reindeer calves were fed infective larvae and examined for worms 48-250 days postinfection. The average length of worms recovered increased asymptotically with time. Gravid females and adult males were recovered from 52 days postinfection (d.p.i.), and the fraction made up by these categories increased with time. Immature females and subadult males were recovered as late as 161 d.p.i. Nematodes were recovered from the spinal subdural space 48-161 d.p.i., from the cranial subdural space 48-90 d.p.i., and from the musculature 90-250 d.p.i. Immature females were found in the spinal subdural space and the cranial subdural space, whereas gravid females were found also in the musculature with an increasing fraction with time. Subadult and adult males were found in all 3 sites but with an increasing fraction of adults from the spinal canal to the cranium to the musculature.

The occurrence of larval ascaridoid nematodes in wild-caught and in caged and artificially fed Atlantic cod, Gadus morhua L., in Norwegian waters.

Abstract Fish farmers have long suspected that farmed cod were less heavily infected with larvae of ascaridoid worms than fish taken in the commercial fisheries. To test this hypothesis, a field experiment was designed to compare the worm burdens of caged and wild-caught fish over a 2-year period. The results showed an increase in the worm burdens of the wild fish but not in the caged fish. It is suggested that the transmission of food-transmitted ascaridoid larvae is broken through artificial feeding, which prevents new infections from establishing in the caged fish. The life expectancy of these worms in cod is probably more than 2 years.

Parasites as biological tags in marine fisheries research: European Atlantic waters

Studies of the use of parasites as biological tags for stock identification and to follow migrations of marine fish, mammals and invertebrates in European Atlantic waters are critically reviewed and evaluated. The region covered includes the North, Baltic, Barents and White Seas plus Icelandic waters, but excludes the Mediterranean and Black Seas. Each fish species or ecological group of species is treated separately. More parasite tag studies have been carried out on Atlantic herring Clupea harengus than on any other species, while cod Gadus morhua have also been the subject of many studies. Other species that have been the subjects of more than one study are: blue whiting Micromesistius poutassou, whiting Merlangius merlangus, haddock Melanogrammus aeglefinus, Norway pout Trisopterus esmarkii, horse mackerel Trachurus trachurus and mackerel Scomber scombrus. Other species are dealt with under the general headings redfishes, flatfish, tunas, anadromous fish, elasmobranchs, marine mammals and invertebrates. A final section highlights how parasites can be, and have been, misused as biological tags, and how this can be avoided. It also reviews recent developments in methodology and parasite genetics, considers the potential effects of climate change on the distributions of both hosts and parasites, and suggests host-parasite systems that should reward further research.

Treatment of reindeer with ivermectin - effect on dung insect fauna

Ivermectin is an antiparasitic drug widely used in reindeer (Rangifer tarandus (L.)) in Fennoscandia and North America. Most of the ivermectin injected in the animal is excreted unchanged in the faeces. Several reports show that ivermectin in cattle dung disrupts colonisation and survival of beneficial dung breeding insects. The present study investigated the effect of ivermectin on the reindeer dung fauna. Four reindeer calves (males, 6 months of age) were injected subcutaneously with standard doses of ivermectin (0.2 mg/kg body weight) in early December. The daily produced faeces was collected until day 30 after treatment, and the concentration of ivermectin was determined by high pressure liquid chromatography (HPLC) with fluorescence detection. The highest concentration measured (mean 1632 ng/g faeces (dry weight), range 907 to 2261 ng/g among the animals) was on day 4 after treatment. The concentration decreased gradually to 28 ng/g (range 6 to 58 ng/g) on day 30. Faeces portions from day 4 and from untreated reindeer were placed in the field on 2-4 July and recollected on 13-22 September in order to detect possible differences in decomposition fauna between the samples. The most important coprophilous beetles (Apbodius spp.) and flies (Scatbophaga spp.) were not detected in this winter dung whether it contained ivermectin or not, probably because of the dry consistency and small size of the pellets. On the other hand, these insects (larvae and imagines) were common in summer dung, which had been deposited naturally in the field and later placed together with the ivermectin-containing winter dung for comparison. The summer dung has a more soft and lumpy consistency. Treatment in autumn or early winter implies that the bulk of the ivermectin from the animal will be present in faeces with winter consistency, since this bulk portion is excreted during the first 30 days after treatment. This dry and pelleted faeces is not utilized by the important coprophilous insecr species, and the current practice of treatment of reindeer with ivermectin in autumn or early winter is therefore the regime representing the least danger of harmful influence on the coprophilous fauna and their contribution to the dung decomposition process.

Search for seasonality in occurrence of parasites of cod, Gadus morhua L. in a fjord at 70°N

Samples of cod from the subarctic fjord, Balsfjord, in Norway, were collected in spring, summer and autumn from spring 1986 to spring 1987. The macroparasite fauna was investigated for seasonality in prevalence, mean intensity and abundance. Anisakis simplex had maximum mean intensity and abundance in the autumn. Echinorhynchus gadi had minimum prevalence, mean intensity and abundance in the autumn, but this was not statistically significant. None of the remaining 11 species of parasites demonstrated seasonality according to our definition.

Clamp ultrastructure of the basal monogenean Chimaericola leptogaster (Leuckart, 1830) (Polyopisthocotylea: Chimaericolidae)

The ultrastructure of the haptoral clamps of the chimaericolid monogenean Chimaericola leptogaster, a basal polyopisthocotylean from the gills of a holocephalan fish, is described. These clamps are characterized by the presence of two muscle blocks interrupted mid-anteriorly and mid-posteriorly and different kinds of hard structures: a single median and paired lateral sclerites embedded in the clamp wall; six spine-like structures directed towards the clamp lumen; and electron dense surface structures along the internal surface of the anterior clamp lips and along the luminal surface of the tegument of the clamp lumen. The lateral sclerites are situated deep within muscular tissue and are closely bounded by radial myofibrils, possessing a uniform electron dense matrix within which are hollow areas of different sizes. The median sclerite occupies an area between the clamp wall myofibrils and the luminal epithelium, is surrounded by a basement lamina and is composed of a heterogeneous matrix comprising two different morphological layers related to variations in the type and concentration of fibrils. Four of the spine-like structures are extensions of the margins of the two spindle-like muscle blocks in the clamps, i.e. the two anterior and two posterior structures, and the two others are situated at the lateral constrictions of the left and right muscle blocks. The electron dense surface structures are derivations of the clamp tegument or, to be more precise, its outer, densely fibrous region. These results are discussed in relation to the evidence that the haptoral clamps of C. leptogaster are apparently ancient origin.

Genetic and morphological variation in Echinorhynchus gadi Zoega in Müller, 1776 (Acanthocephala: Echinorhynchidae) from Atlantic cod Gadus morhua L.

Previous studies have shown considerable variability in morphological features and the existence of genetically distinct sibling species in the acanthocephalan Echinorhynchus gadi Zoega in Müller, 1776. The aim of the present study was to follow up and extend those earlier studies by using a combination of DNA analysis and morphometrics to investigate differences between samples of E. gadi from Atlantic cod Gadus morhua L. caught at five fishing grounds in the Baltic Sea and three in different parts of the North Atlantic. Twelve morphological features were measured in 431 specimens of E. gadi, 99 individuals were studied by polymerase chain reaction-restriction fragment length polymorphosm (PCR-RFLP), and selected PCR products were sequenced. The molecular analyses showed the nucleotide sequences of E. gadi rDNA from cod caught at all the sampling sites to be identical. The comparative morphological study, in contrast, revealed significant differences between samples of E. gadi from different sampling sites and showed the separation of E. gadi into two groups corresponding approximately to the systematic classification of cod into the two subspecies, Atlantic G. morhua morhua and Baltic G. morhua callarias. The E. gadi infrapopulation size had a significant effect on some of the morphological features. The results are discussed in relation to cod population biology, the hydrography of the study area and the history of the Baltic Sea formation.