We report the infection levels of third-stage anisakid larva in the muscle of the Argentinean hake, Merluccius hubbsi, in relation to fish size and location in the musculature. The musculature of 42 hake was separated into hypaxial (ventral) and epiaxial (dorsal) parts and surveyed for nematode larvae. Two anisakid species were detected: Anisakis sp. (prevalence, 52.4%; mean +/- SD abundance, 1.2 +/- 1.7) and Pseudoterranova sp. (prevalence, 9.5%; mean +/- SD abundance, 0.2 +/- 0.7). Since the fish were gutted after capture, the occurrence of anisakids in the flesh indicates that the worms had migrated into the muscle before capture. The number of Anisakis sp. in muscle was not correlated with fish length or weight. Therefore, fish size cannot be used as a predictor of parasite loads in the muscle. Only one Anisakis sp. and one Pseudoterranova sp. appeared in the epiaxial musculature. The density of Anisakis sp. in the hypaxial muscles was significantly higher than that in the epiaxial ones. This suggests that removal of the hypaxial musculature can reduce the risk of anisakid-induced allergies and gastrointestinal anisakidoses among consumers.

The population structure and habitat selection of Anisakis simplex in 35 harbor porpoises off Denmark are described. The nematodes were collected from the stomach and duodenal ampulla and were categorized as third-stage larvae, fourth-stage larvae, subadults, and adults. The porpoises harbored 8,043 specimens of A. simplex. The proportion of adults and subadults increased with infrapopulation size. The number of development stages across infrapopulations covaried significantly (Kendall's test of concordance). Concordance was higher in hosts with the highest intensities than in those with low and medium intensities. All stages occurred mainly in the forestomach, but this trend was stronger for the adults. Adult and subadult sex ratios did not depart significantly from 1:1. Our data suggested that recruitment and duration of each stage were the main factors accounting for infrapopulation structure. The preference of A. simplex for the forestomach conformed with previous studies, but the narrower distribution of adults relative to other stages might indicate a strategy to enhance mating opportunities. Information on sex ratios of A. simplex is scarce and contradictory. We suggest that the discrepancies might partly reflect differences in categorization criteria and statistical methods.The occurrence of third-stage larvae (L3) of anisakid nematodes in the fillets of commercial fish entails well-known public health concerns and economic repercussions (Burt, 1994;Smith, 1999). Consequently, the population ecology of anisakid nematodes has received more attention than that of any other parasite of marine mammals. Most population studies of anisakids have focused on describing the population structure and dynamics of the sealworm, Pseudoterranova decipiens, and other species common in seals (see Bowen 1990; Desportes and McClelland 2001, and references therein for examples) and have produced valuable data on the life history and population ecology of these nematode species.As for the whaleworm, Anisakis simplex, most population studies have focused on its intermediate and paratenic hosts (Brattey and Bishop, 1992;Herreras et al., 2000;Podolska and Harbowy, 2003), whereas its population biology in the definitive hosts has been less studied. Most information on the definitive hosts concerns the harbor porpoise, Phocoena phocoena, a small odontocete common in the Northern Hemisphere (Smith, 1989;Brattey and Stenson, 1995;Herreras et al., 1997). The data on the population structure of A. simplex in this cetacean are based on small sample sizes (Young, 1972;Smith, 1989) or lack details of the infrapopulation structure (Lick, 1991;Brattey and Stenson, 1995). These 2 shortcomings are also common in studies of this nematode in other cetacean species (e.g., Wazura et al., 1986;Raga and Balbuena, 1993). Moreover, little is known about habitat selection by A. simplex in the definitive hosts. To our knowledge, there are only 2 studies providing such information (Brattey and Stenson, 1995;Aznar et al., 2003), and only the ...

Studies reporting numbers of eggs in vagina and utero in nematodes often give little information of the technique used for the estimations. This situation hampers comparison among studies, because, so far, differences in estimations provided by different techniques have not been assessed. This note examines whether a manual method based on visual counts in aliquots and an automated method using a Coulter counter yield equivalent estimations of egg numbers in vagina and utero of 3 anisakid nematode species (Anisakis simplex, Pseudoterranova decipiens, and Contracaecum osculatum). The number of eggs from 50 females per nematode species was estimated using both techniques. The automated and manual methods yielded similar egg counts (correlation coefficients >0.9 in the 3 species), but the methods were not always statistically equivalent. The automated method was more precise and seemed less dependent on egg density, whereas the manual method was less time-consuming (contrary to previous perceptions) and less expensive. Despite the higher precision of automated counts, the manual technique seemed to produce similar estimates; thus, it may be particularly useful in developing countries where nematode parasitism is prevalent in humans and domestic animals, but scientific resources are limited.

Phenotypic tradeoffs between number and size of eggs were tested in three component populations of three marine anisakid nematodes: Anisakis simplex , Pseudoterranova decipiens and Contracaecum osculatum . Body and uterine volumes (as proxies of female size), and egg number, mean egg volume and clutch volume (as descriptors of reproductive output) were measured in 50 females of each species. Evidence of a phenotypic tradeoff was detected only in A. simplex ; the first time that has been found in a parasite population. Comparison of feasible values inferred from the van Noordwijk and de Jong's model and current data showed that interindividual variation in egg size was narrower than expected in the three populations. Structural constrictions in response to optimal allocation rules might account for this pattern. In P. decipiens and C. osculatum variation in egg size was the lowest and independent of female size, suggesting that the tradeoff is absent, rather than being present but masked by unaccounted variables. Spatial constrictions imposed by uterine size seemed to play an important role determining the emergence of the tradeoffs. So factors accounting for the tradeoff in A. simplex are probably constructional rather than physiological. Individual variability in investment in clutch volume was similar to previous studies but variation in allocation between number and size of eggs was much smaller than that reported previously. Perhaps differences in life-history strategies might explain this because the nematodes studied are either semelparous or short-lived iteroparus organisms whereas previous data derive from long-lived iteroparous ones. Despite the perception that parasites live in resource-rich habitats, the present study indicates that patterns relating number and size of eggs might not differ much from those observed in free-living populations and thus the same range of factors would operate in both types of organisms.The reproductive output of any individual can be partitioned into two components, propagule number and propagule size. The relationship between them is still poorly known in parasites, where only two studies concerning Graphidioides subterraneus , a parasitic nematode of rodents (Rossin et al. 2005), and Lernanthropus cynoscicola, a copepod parasite on fish (Timi et al. 2005), have been carried out at population level. Because both components compete directly for the limited energy budget and/or for the limited space within a mother, a tradeoff between them is expected. Previous studies (including the two of parasites mentioned above) have used correlations between number and size of eggs in order to test for the occurrence of this phenotypic tradeoff. It has been argued that this approach is of limited value because (1) it is impossible to infer causation from correlation, (2) environmental variation may mask or accentuate the correlation, and (3) phenotypic correlations do not demonstrate genetic control of the tradeoffs (Reznick 1985, Lessells et al. 1989. However, when selection acts on...

Phenotypic tradeoffs between number and size of eggs were tested in three component populations of three marine anisakid nematodes: Anisakis simplex , Pseudoterranova decipiens and Contracaecum osculatum . Body and uterine volumes (as proxies of female size), and egg number, mean egg volume and clutch volume (as descriptors of reproductive output) were measured in 50 females of each species. Evidence of a phenotypic tradeoff was detected only in A. simplex ; the first time that has been found in a parasite population. Comparison of feasible values inferred from the van Noordwijk and de Jong's model and current data showed that interindividual variation in egg size was narrower than expected in the three populations. Structural constrictions in response to optimal allocation rules might account for this pattern. In P. decipiens and C. osculatum variation in egg size was the lowest and independent of female size, suggesting that the tradeoff is absent, rather than being present but masked by unaccounted variables. Spatial constrictions imposed by uterine size seemed to play an important role determining the emergence of the tradeoffs. So factors accounting for the tradeoff in A. simplex are probably constructional rather than physiological. Individual variability in investment in clutch volume was similar to previous studies but variation in allocation between number and size of eggs was much smaller than that reported previously. Perhaps differences in life-history strategies might explain this because the nematodes studied are either semelparous or short-lived iteroparus organisms whereas previous data derive from long-lived iteroparous ones. Despite the perception that parasites live in resource-rich habitats, the present study indicates that patterns relating number and size of eggs might not differ much from those observed in free-living populations and thus the same range of factors would operate in both types of organisms.