An in vitro study of lipid preference in whaleworm (Anisakis simplex, Nematoda, Ascaridoidea, Anisakidae) third-stage larvae.

The behavioural response of nematodes to chemical stimuli has been extensively investigated in some free-living and plant parasitic species. However, in animal parasitic species, little is yet known, particularly in regards to marine forms such as the whaleworm (Anisakis simplex). Previous studies showed that A. simplex L3-larvae tend to prefer fish tissue with high lipid content. The intention of this study was to investigate the behaviour of A. simplex L3 in response to different concentrations of fish lipid in further detail. This was done by an in vitro study based on larvae from cod (Gadus morhua). Ten larvae were placed in each of the culture containers containing agar that was separated into three segments of equal size. Three categories of agar were used containing 0, 2 and 7% cod liver oil. A total of 900 larvae were included. The study consisted of three parts: The purpose of experiment I was to establish whether different lipid concentrations influenced the migration pattern at all. Experiment II was intended to examine whether A. simplex L3-larvae were able to actively search for lipids. Experiment III was set up to analyse the short-distance dispersion of the L3-larvae. Experiment I indicated that the L3-larvae move randomly but do not stop randomly since the tendency to move out of the start area was inversely correlated with lipid concentration. Experiment II indicates that the larvae are almost unable to select areas of high lipid concentrations when more than a few centimetres away. Experiment III showed that the L3-larvae prefer high-fat content and can seek it out over short distances.

Growth, fecundity and sex ratio of adult whaleworm (Anisakis simplex; Nematoda, Ascaridoidea, Anisakidae) in three whale species from the North-East Atlantic.

The growth rate, fecundity, and sex ratio of Anisakis simplex in minke whales (Balaenoptera acutorostrata), porpoises (Phocoena phocoena) and long-finned pilot whales (Globicephala melas) was studied on the basis of material from the North Atlantic. A total of 8,135 mature A. simplex were collected from 24 minke whales, 11 porpoises and eight pilot whales. For both males and females, the prevalence was 100% for all three host species, with a mean intensity of 1,727, 262 and 139, respectively. The mean body length of adult female A. simplex was 126 mm in minke whales, 71 mm in the porpoises and 73 mm in pilot whales; and for males the averages were, respectively, 106 mm, 57 mm and 68 mm. Eggs from the uteri of 32 females of length 87-176 mm collected in minke whale stomachs were counted in a Fuchs-Rosenthal chamber. Total egg production was measured in 14 females cultivated at sea. The female growth period was estimated to be 30-60 days, and apparently all eggs were shed during the last week of life. A female of size 150 mm produces approximately 1.5 million eggs. In the cultivation experiment, about 85% of the total egg production was shed during the first 3 days after spawning started.

Growth of whaleworm (Anisakis simplex, Nematodes, Ascaridoidea, Anisakidae) third-stage larvae in paratenic fish hosts.

The growth of Anisakis simplex L3 larvae in the three paratenic hosts saithe ( Pollachius virens), cod (Gadus morhua) and redfish (Sebastes marinus) was studied based on material collected off the island of Vega on the west coast of Norway over a period of 1 year. In all three fish species, a positive correlation between the length of larvae and the age of the fish was shown. The number of large larvae, here defined as L3>28 mm, increases with increasing age of the host. These findings clearly indicate an accumulation of large L3 larvae and larval growth in the fish host. The larvae were additionally grouped according to the tissue--muscle, liver or other viscera--they were located in. When the average lengths of the three groups of larvae were compared, the gadoids saithe and cod had somewhat higher values for L3 larvae found in the liver. Redfish, on the other hand, which store fat to a relatively higher degree in the viscera, had the highest average length of larvae in this tissue. The lowest average values in all three species were found in the musculature. These trends suggest that the growth of A. simplex L3 larvae is positively correlated with the fat content of the tissue in which it is encapsulated. Of the three host species included in this study, saithe seemed to be the best suited for A. simplex L3, as the growth rate and average length of the parasite was greatest in this species. The growth and average length of L3 was least pronounced in redfish while cod held an intermediate position.