Karin Andersen

Distribution of whaleworm (Anisakis simplex, Nematoda, Ascaridoidea) L3 larvae in three species of marine fish; saithe (Pollachius virens (L.)), cod (Gadus morhua L.) and redfish (Sebastes marinus (L.)) from Norwegian waters

Abstract The frequency distribution of Anisakis simplex L3 larvae between host tissues was investigated in three host species: saithe, cod and redfish. Fish were sampled from Norwegian coastal waters and examined for the presence of A. simplex in muscle and viscera. In all three of the host species, A. simplex larvae were most frequently detected in the viscera; the percentages of total infection for saithe, cod and redfish were 99.6%, 97.8% and 88.0%, respectively. In general, the distribution patterns of A. simplex L3 between muscle and viscera were not significantly affected by host size. The observations that distributions vary between species and are not affected by host size do not support an earlier hypothesis which states that A. simplex L3 distributions are determined by an optimal pre-encapsulation migratory distance within host tissues. In contrast, it is suggested that A. simplex L3 distributions are governed by the conditions encountered within host tissues, and are possibly related to the availability of nutrients.

A key to three species of larval Diphyllobothrium Cobbold, 1858 (Cestoda: Pseudophyllidea) occurring in European and North American freshwater fishes.

A key is presented to the plerocercoids of the three species of Diphyllobothrium frequently occurring in fishes of Europe and North America. The key is intended for use by both helminthologists and fish biologists. It is designed in four parts: readily visible features of gross-morphology; body-size and site data; features of gross-morphology more clearly seen under the scanning electron microscope; and features visible in histological sections.

“Spring rise” of whaleworm (Anisakis simplex; Nematoda, Ascaridoidea) third-stage larvae in some fish species from Norwegian waters

Abstract The seasonal variation in the infection of saithe (Pollachius virens), cod (Gadus morhua), and redfish (Sebastes marinus) from a coastal area of central Norway with Anisakis simplex third-stage larvae (L3) was studied over a period of 1 year. In all three host species there was an increase in the abundance of the parasite in spring, with a peak appearing in March and April. Cod displayed the most distinct seasonal variation, showing a clear abundance peak in April. The abundance peak in April for redfish was not as pronounced. In saithe the abundance over the seasons was less prominent, with a maximum appearing in March and another increase in abundance occurring during July. It is apparent that the causes behind the pattern of infection observed in this study are complex. However, possible explanatory mechanisms are discussed. Arguments are propounded to suggest that the increased supply of parasite eggs from northward-migrating whales in addition to the general spring bloom of plankton constitute the most important factors governing the phenomenon of “spring rise” in A. simplex L3 in the study area.

Comparison of surface topography of three species of Diphyllobothrium (Cestoda, pseudophyllidea) by scanning electron microscopy

Abstract Plerocercoids of different sizes as well as adult worms of D. dendriticum, D. latum and D. ditremum were studied using scanning electron microscopy (S.E.M.). In the plerocercoids there were found distinct differences in appearance and length of microtriches between these three species, while the microtriches of adult worms were more similar. A regional difference in microtrix appearance was found in the larvae of D. ditremum and D. dendriticum . This was not apparent with S.E.M. in adult worms. The length of ‘body’ microtriches in D. dendriticum varied with the length of the larvae. The topography of the genital atrium of mature and gravid proglottids in adult worms of these three species is also described.

Ultrastructural studies on Diphyllobothrium ditremum and D. dendriticum (Cestoda, Pseudophyllidea), with emphasis on the scolex tegument and the tegument in the area around the genital atrium

SummaryThe scolices of D. ditremum and D. dendriticum are similar in regard to general morphology and ultrastructure of the tegument. At the scolex apex and along the upper bothrial edges sensory endings are numerous. The inner bothrium surface of D. ditremum appears to be plain or smooth, the distal cytoplasm is only about 0.6 μm thick and covered with long and slender microtriches. When D. ditremum is attached to the host gut an adhesive layer of secreted substance exists between the inner bothrium surface and the host intestinal villi. In D. dendriticum, however, no secreted layer exists between the inner bothrium surface and the host intestinal villi and the inner bothrium surface of this species appears to be lobed or lappet formed. The lobes are protrusions of the distal cytoplasm and are covered with long and slender microtriches. Large conglomerations of secretion globules appearing to be enclosed by a double membrane, are observed in the scolices of D. dendriticum and D. ditremum, although more frequent in the latter. Differences existing between the distal cytoplasm of the scolex and the gravid proglottid are described. The papillae around the genital atrium in mature and gravid segments were studied. Each papilla appears as a thickening of the distal cytoplasm, which in this region is 10–12 μm thick, when studied with transmission electron microscope. From the area between the papillae sensory endings appearing in sections to be either single, double or triple are described.

The functional morphology of the scolex of Diphyllobothrium cobbold (Cestoda, Pseudo-phyllidea). A scanning electron and light microscopical study on scoleces of adult D. dendriticum (Nitzsch), D. latum (L.) and D. ditremum (Creplin)

Abstract Scoleces of adult D. dendriticum, D. latum and D. ditremum were studied using scanning electron and light microscopy. In D. dendriticum and D. latum the transverse bar between the bothria at the scolex apex always possessed a frontal pit while in D. ditremum no such invagination was seen. The scoleces attach to the host intestine by taking a firm grip with each bothrium around one or two intestinal villi. In D. ditremum and D. latum a layer of secreted substance is present between the scolex apex and the host intestine and between the inner bothrium surface and the host intestinal villi. In D. dendriticum , however, such a secreted layer was only observed at the scolex apex. A general account of the musculature and nervous and excretory systems of a Diphyllobothrium scolex is given.

Studies on the scolex morphology ofEubothrium spp. with emphasis on characters usable in species discrimination and with brief references on the scolices ofBothriocephalus sp. andTriaenophorus spp. (Cestoda; Pseudophyllidea)

SummaryScolices ofEubothrium crassum from brown trout,E. salvelini from char,E. parvum from mallotus,Bothriocephalus sp. from three-spined stickleback, andTriaenophorus spp. from pike were studied using scanning electron microscopy (S.E.M.) and light microscopy, only the two first mentioned species were sectioned for transmission electron microscopy (T.E.M.). All scoleces examined with S.E.M. were characterized by ‘spherical bodies’ appearing on the scolex surface. Studied with T.E.M. these ‘bodies’ turned out to be cytoplasmic protrusions containing secretory granules. These protrusions seemed to be nipped off as globular structures which freed single secretory granules.The present study also emphasizes the use of S.E.M. as a tool in cestode taxonomy and clarifies some of the problems and confusion that have surrounded the scolex morphology and shape ofE. crassum andE. salvelini.

A marine Diphyllobothrium plerocercoid (cestoda, pseudophyllidea) from blue whiting (micromestius poutasson).

SummaryA type of Diphyllobothrium plerocercoid found in blue whiting, Micromestius poutasson, caught near the north edge of the Faeroe Banks, is described. The most dominant characters of these larvae are their typical dorsoventrally flattened body and their fully extruded and “adult”-like scolex. A morphological comparison with perocercoids of D. dendriticum, D. ditremum and D. latum is given.

Variation in Scolex Morphology within and between Some Species of the Genus Proteocephalus Weinland (Cestoda, Proteocephala) with References to Strobilar Morphology

The scolex morphology of some Proteocephalus species from fish caught in fresh and brackish waters in Norway, as revealed by scanning and transmission electron microscopy and light microscopy, is described. The size and form of the fifth apical sucker proved to be a very pure character for identification. In spite of this, however, the scoleces of different species revealed specific characters which together with strobilar characters should be well suited for species discrimination and identification.

Hysterothylacium aduncum (Rudolphi, 1862) infection in cod from the Oslofjord: seasonal occurrence of third- and fourth-stage larvae as well as adult worms

Hysterothylacium aduncum infections in cod from the Oslofjord were followed for 1 year. The recovered worms were grouped according to developmental stage [third-stage larvae (L3), fourth-stage larvae (L4) and adult worms] and according to location (in the gut or encapsulated on the viscera). The cod were found to be infected withH. aduncum (all stages lumped) throughout the whole year, with the prevalence approaching 100%. The abundance of the parasites (mean number per fish studied), however, was clearly lowest during the summer months. L3 and L4 recovered from the intestine dominated most of the time but showed a very clear peak during late winter and early spring. L3 recovered from the body cavity was the only stage that showed a clear peak during the summer months. Adult worms, although adult worms were present in very small numbers throughout the year, they tended to peak in May and then again in December and January. Since there did not seem to be a correlation between the accumulation of L3 in the body cavity and the length or age of the fish, the possibility of self-infection whereby the larvae reenter the gut and continue to develop into L4 and then into adults, is discussed.