Bjørn Berland

Genetic evidence for three species within Pseudoterranova decipiens (nematoda, ascaridida, ascaridoidea) in the north atlantic and norwegian and barents seas

Genetic variation of 1017 specimens of codworm, Pseudoterranova decipiens, collected from fish and seals at 23 sampling locations in the North Atlantic and Norwegian and Barents Seas, was analysed on the basis of 16 enzyme loci. Three reproductively isolated species, provisionally designated P. decipiens A, B and C, were detected, showing distinct alleles at the following loci: Mdh-1, 6Pgdh, Np, Pgm, Est-2 (between species A and B); Mdh-3, 6Pgdh, Np, Sod-1, Adk, Pgm, Est-2, Mpi (between A and C); Mdh-1, Mdh-3, Sod-1, Adk, Pgm, Est-2, Mpi (between B and C). One F1 hybrid was observed between P. decipiens A and B, but this apparently does not lead to any gene exchange between the two species, which do not show any evidence of introgression. No hybrids or introgressed individuals were observed between P. decipiens C and either A or B. Genetic distances among conspecific populations were low (average Neis D 0.001-0.005), even though they were collected thousands of kilometres apart, indicating high levels of gene flow within each of the three species. The values of Neis index D were 0.44 between P. decipiens A and B, 0.57 between B and C, and 0.79 between A and C. Estimated evolutionary divergence times, using Neis formula, range from 2 to 4 million years. Differences between P. decipiens A, B and C were also found with respect to genetic variability, morphology, geographical distribution and hosts. Mean heterozygosity values of 0.08, 0.05 and 0.02 were obtained for P. decipiens A, B and C, respectively. Preliminary morphological examination of adult males, previously identified by multilocus electrophoresis, revealed differences in the relative size and pattern of caudal papillae. P. decipiens B is widespread in the study area, whereas P. decipiens A was found only in the North-East Atlantic and Norwegian Sea. In this area P. decipiens A is most common in the grey seal, Halichoerus grypus, while the common seal, Phoca vitulina, is the main host for P. decipiens B. In Canadian Atlantic waters, where P. decipiens A is apparently absent, P. decipiens B infects both grey and common seals; a few specimens were also found in the hooded seal, Cystophora cristata. The only definitive host so far identified for P. decipiens C is the bearded seal, Erignathus barbatus; P. decipiens C appears to be widespread, occurring in both the North-West Atlantic and Barents Sea.

Three sibling species within Contracaecum osculatum (nematoda, ascaridida, ascaridoidea) from the atlantic arctic-boreal region: Reproductive isolation and host preferences

Genetic variation within and between population samples from 22 locations of the Atlantic Arctic-Boreal region, including 1657 specimens morphologically assigned to Contracaecum osculatum, was electrophoretically analysed at 17 loci. Highly significant deviations from the Hardy-Weinberg equilibrium were found at various loci in several samples, owing to the existence of three distinct gene pools within C. osculatum (sensu lato) from the study area. These gene pools correspond to three biological species (provisionally designated A, B and C), characterized by distinct genotypes at several diagnostic loci. Reproductive isolation between C.osculatum A, B and C is confirmed by the lack of F1, recombinant, or backcross genotypes in sympatric areas, despite the occurrence of multiple infections. Mean heterozygosity per locus is on average 0.11 in species A, 0.10 in B and 0.07 in C. High levels of gene flow were found within each of the three species, the values of Nm (number of migrant individuals) ranging from 3.41 (C. osculatum C) to 5.77 (C. osculatum A). Average Neis genetic distance is 0.46 between A and B, 0.50 between A and C and 0.77 between B and C. From these values, times of evolutionary divergence from 2 to 4 million years can be estimated. Genetic relationships among populations and species of the C. osculatum complex are illustrated by principal component analysis. The role of both geographical isolation and host preferences in the speciation of C. osculatum (sensu lato) is discussed. A morphological distinction of the three species has not yet been possible (sibling species). However, there is evidence that the name C. osculatum (sensu stricto) should be used for species C, which shows a geographical distribution and definitive host corresponding to the neotype of C. osculatum (sensu stricto). Finally, a comparison is made between the members of the C. osculatum complex from the Atlantic Arctic-Boreal region and those of the Pseudoterranova decipiens complex from the same area, as to: (i) times of evolutionary divergence, (ii) geographical distribution, and (iii) host preferences.

Low detection efficiency of candling as a commonly recommended inspection method for nematode larvae in the flesh of pelagic fish

The third-stage larvae of the parasitic nematode Anisakis simplex commonly occur in most commercially important fish species from the North Atlantic. In this study, the occurrence and site distribution of Anisakis larvae in various size groups of Norwegian spring spawning herring (Clupea harengus), blue whiting (Micromesistius poutassou), and mackerel (Scomber scombrus) from the Northeast Atlantic was investigated. Although most of the larvae were found in the abdominal cavity, the small proportion lodged in the flesh was sufficient to affect food quality and safety. However, the prevalence of Anisakis larvae in fish fillets varied considerably among the size groups of each species: 15 to 60% in herring, 32 to 77% in mackerel, and 89 to 100% in blue whiting. The commonly recommended nematode detection method in the fish processing industry is candling, i.e., a brief visual inspection on a light table. Comparison of successively more accurate detection methods, i.e., candling, enzymatic degradation, and UV illumination, for fillets of each fish species revealed that only 7 to 10% of the nematode larvae present in the fillets were detected by candling. The candling efficiency was apparently independent of fillet thickness. Thus, candling is not sufficient to detect the majority of the nematodes that are actually present in the fillets of pelagic fish from the Northeast Atlantic. These findings emphasize the importance of adequate deep-freezing of any fresh pelagic fish product, especially if it is intended for consumption in a raw or semiraw state.

A report on some metazoan parasites of wild marine salmon (Salmo salar L.) from the west coast of Norway with comments on their interactions with farmed salmon

Abstract A survey of metazoan parasites of wild salmon returning to western Norway revealed copepod, nematode, cestode and trematode species to be present. Two species, the copepod Lepeophtheirus salmonis and the cestode Eubothrium sp., are currently known to cause serious economic losses in Norwegian salmon farming. Larvae of the nematode species Anisakis simplex , while not currently a problem in farmed salmon, are a well known problem in wild fisheries. The prevalence and distribution of each species are presented for both wild and farmed salmon, where known, and discussed in light of present day knowledge of the life cycles of the individual species.

On the morphology of the head in four species of the Cucullanidae (Nematoda)

Abstract The morphology of the head, mouth, and oesophagus in four species of the nematode family Cucullanidae Cobbold, 1864, has been studied in detail. The species examined are: Cucullanus cirratus Muller, 1777 and C. heterochrous Rudolphi, 1802 from the west coast of Norway, C. minutus Rudolphi, 1819 from Scotland, and Dacnitis truttae (Fabricius, 1794) from east Norway; the first three are from marine fish, the last from a freshwater fish. In the Cucullanus species, transverse cuticular structures projecting into the muscle mass from the pseudobuccal capsule are described, illustrated, and named. Such projections are absent in Dacnitis, but the pseudobuccal cuticular lining forms thickened plates separated by narrow grooves which form a characteristic pattern. The morphology of the pseudobuccal capsule and its associated cuticular structures may be used as taxonomic characters at the species level, possibly also at genus and higher levels. A new definition of Dacnitis is proposed. The functional signi...

The effect of long term, low level Eubothrium sp. (Cestoda: Pseudophyllidea) infection on growth in farmed salmon ( Salmo salar L.)

Abstract Loss of potential growth in farmed salmon with persistent low-grade infection of Eubothrium sp. is shown to be approximately 450 g per fish for females and 800 g per fish for males. The systematics of Eubothrium sp. are discussed with regard to Eubothrium crassum and its sibling species in relation to salmon farming. The epidemiological implications of the infections are discussed with regard to aquaculture.

On the ecology and distribution of Pseudoterranova decipiens C (Nematoda: Anisakidae) in an intermediate host, Hippoglossoides platessoides, in northern Norwegian waters

The distribution of Pseudoterranova decipiens C helps demonstrate the ecological basis of this genetically defined sibling species. In northern Norwegian waters the major fish intermediate host is Hippoglossoides platessoides. Overall prevalence, mean intensity and intensity range in H. platessoides were 15%, 16.5 and 1-165, respectively. Outside the range of its only known definitive host, the seal Erignathus barbatus, the parasite was not found in the same intermediate host.

Sealworm (Pseudoterranova decipiens) infection in common seals (Phoca vitulina) and potential intermediate fish hosts from the outer Oslofjord

Infection with Pseudoterranova decipiens in 45 common seals (Phoca vitulina) from the outer Oslofjord was investigated. Seals were collected before and during the phocine distemper virus epizootic in 1988 when the seal population in the area was reduced from about 350 to 100. In 1989, cod (Gadus morhua) and other fish species were sampled for comparison with earlier investigations on prevalence and abundance of P. decipiens infection in fishes from the outer Oslofjord. Seventy-two per cent of cod were infected with P. decipiens larvae in shallow waters between the seal skerries; the corresponding abundance was 2.2. At other fishing sites at increasing distances from the seal colony, abundance dropped to 0.05-0.20. Otoliths recovered from stomachs and scats indicated that gadids (Micromesistius poutassu, Trisopterus esmarkii and G. morhua) made up more than 80% of the seal diet. Bullrout (Myxocephalus scorpius) was also heavily infected with P. decipiens (prevalence 93% and abundance 8.4), but was not found in the seal diet. However, uninfected cod that enter shallow water from the surrounding deep waters became infected when they feed on bullrout. Recruitment to mature stock of P. decipiens occurs when highly infected cod are eaten by seals. The number of reproducing P. decipiens is very low in common seals. Only 2 seals (i.e. less than 5% of the sample) were simultaneously infected with mature worms of both sexes. The dramatic reduction of the seal stock in the outer Oslofjord by the epizootic did not seem to affect the abundance of P. decipiens in its intermediate hosts.

The Morphology of Thynnascaris adunca (Rudolphi) (Nematoda, Ascaridoidea)

The following body parts of the fish nematode Thynnascaris adunca were studied by using SEM and TEM: anterior and posterior ends, digestive tract, particularly the oesophagus and its glandular tissue, male and female reproductive organs, excretory and nervous systems, and body wall. The ova in the uterus of a female studied by SEM were found to contain II‐stage larvae: this is at variance with previous reports. Contrary to accepted views, each body wall muscle was found to have more than one process (“arm”) reaching the dorsal/ventral nerve.

Description of Ascarophis arctica Poljansky, 1952 (Nematoda: Cystidicolidae) in Baltic Sea fishes

Ascarophis arctica Poljansky, 1952 (Nematoda: Cystidicolidae) is described. The parasites were obtained mainly from the four-horn sculpin, Myoxocephalus quadricornis (L.), from the northern Baltic Sea, but also from Zoarces viviparus (L.) from the southern Baltic. The description is based on LM and SEM studies. Worms were found close to the mucosa of the distal part of the stomach. The fact that Ascarophis arctica is common in the four-horn sculpin suggests that in the Baltic Sea it is a glacial relict. The record of this species in Zoarces viviparus does cast some doubt upon this view.