J Parasitol. Aug;75(4) Changes in numbers and growth of Ligula intestinalis in the spottail shiner (Notropis hudsonius), and their roles in. Abstract. The tapeworm Ligula intestinalis occurs in the body cavity of its cyprinid second intermediate host, in this study the roach Rutilus rutilus, and inhibits. Since its use as a model to study metazoan parasite culture and in vitro development, the plerocercoid of the tapeworm, Ligula intestinalis, has.

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Young infected roach, 2 and lntestinalis years old, rarely attained the same body weight as their non-infected counterparts mean body mass: Orrpheromonal stimuli which would normally be received within the group-shoaling situation are absent from infected individuals, which may enhance the delay in puberty Francis et al. In addition, GSI recorded in this infection suggested that non-infected host populations were undergoing normal reproductive cycles.

Because of the small amount of gonadal tissue in infected roach weighing less than 0. Gonadal development Because of the small amount of gonadal tissue in infected roach weighing less than 0. Although this effect was dose dependent, significant intesstinalis were found between Ligula and a related tapeworm species, Schistocephalus solidus. Whether this is mediated by direct effects of Ligula products or general endocrine disruption requires elucidation.

This not only supports the hypothesis by Arme that reproductive inhibitory effects are specific to Ligulabut also suggests that effects of the parasite extend to non-host species e. The latter has been demonstrated in other cyprinids where positive and negative responses have been noted for GnRH and dopamine respectively for review see Peter et al.

Plerocercoids were most prevalent 5. Indeed, sexual maturation will occur every year in non-infected fish but not in infected ones. Because of the very small amount of gonadal tissue present in infected fish, and thus the problem of finding and confirming the presence of gonads intestnialis histological examination, the condition factor was calculated including the gonadal tissue in parasitised individuals.

I, infected fish; NI, non-infected fish; F, female; M, male. Previous observations have revealed that two GnRH forms salmon and chicken occurred in the brain of non-infected and infected roach Williams et al.

However, because of the low sample size in certain age classes of infected fish, body lengths were considered according to age class, and differences were less apparent. The fragments and nucleotides respectively obtained were cloned and sequenced Genbank accession numbers: However, seasonal variations in pituitary LH content observed in non-infected fish were absent in infected roach. Introduction Previous studies have revealed that several parasitic infections can affect host reproduction.


Materials and methods Fish Ligulosed and non-ligulosed roach were collected from the Altami Angling Club, Chester, Cheshire, UK during ljgula at three times during the reproductive year: The use of a heterologous assay for carp LH was fully justified in view of the high level of sequence identity of the roach molecule see below.

Some of the contradictions in the literature may be attributed to underestimated prevalence due to increased numbers of spawning fish in the spring, mixed age-classes of Ligula in separate age-classes of fish, and differential effects on growth due to infection in male versus female hosts.

Eighteen species of fishes were collected during the open water and winter seasons from Dauphin Lake, Manitoba, Canada 51 degrees 17’N, 99 degrees 48’W and examined for plerocercoids of Ligula intestinalis L. Figure 2 shows the condition factor of fish according to age, showing lower K values in infected fish, reflecting the fact that non-infected individuals are in better condition, irrespective of age, than their infected counterparts.

Details of fish used and effects of parasitism are shown in Table 1. As has been noted previously by Kennedy et al. It may not be surprising, therefore, that the presence of a large parasite burden, which could be considered as a potent stressor, resulted in the observed dramatic effects on host reproduction. A subset of four non-infected female fish from each group was used for histological analysis of gonadal development and two categories of oocytes were observed, i.

Investigations of the effect of Ligula on the production of the other gonadotrophin follicle-stimulating hormone are also required, especially considering the potential effect of the parasites on the early stages of gametogenesis.

In contrast, in infected fish, only these immature stages of oogenesis were present throughout and no cyclical variations were recorded see Arme Ligula intestinaliswhich is found in the body cavity of certain cyprinid fish, inhibits reproduction in both male and female fish.

While roach were caught up to 54 g in weight, fish exceeding 20 g were not infected with Ligula Fig. This suggested that Ligula infection decreases LH synthesis by inhibiting its expression and indicates that the levels of gonadotrophin-producing cells being affected by parasitisation are critical to normal reproductive function.

Given that fish infected with Ligula intestinalis do not exhibit normal behaviour patterns in terms of shoaling e. This abnormal behaviour may also expose roach to different light intensities, a parameter vitally important in the control of the reproductive cycle in fish Bromage et al.


Ligula intestinalis (Cestoda: Pseudophyllidea): an ideal fish-metazoan parasite model?

GSI leading up to spawning February varied between 0. Although this phenomenon has been reported several times e. As with length, in 4 year-old fish there was no statistically significant difference between the body mass of infected and non-infected individuals infected 8. The fact that this inhibition was not observed when we compared older fish may arise from the negative effect of sexual maturation on growth and condition e.

Previous studies have indicated effects of infection at the pituitary gland level. This appears to be related to the greater metabolic stress on infected males.

Ligula intestinalis (Cestoda: Pseudophyllidea): an ideal fish-metazoan parasite model?

Previous studies have revealed that several parasitic infections can affect host reproduction. Analysis of host and parasite growth revealed that the soma of male spottails infected with Ligula weighed more but had a reduced growth rate.

Discussion Our results have confirmed previous observations made by Armeon the biometric effects of Ligula intestinalis on its roach intermediate host. Whilst it is true that gonadotrophs are much reduced in number, the cells that are present do appear to be functional, indicating that Ligula infection neither completely prevents gonadotroph differentiation nor basal activity.

Importantly, it also revealed that the roach—parasite interaction under investigation is typical of that found in other sampled populations. In the roach, our data also showed that Ligula infection exerts some inhibitory effects on body growth and condition, but these effects are small and would, therefore, not account for the complete blockade intestinzlis puberty noted in ligulosed fish.

Correlations between body parameters were subjected to regression analysis. The effects noted in the wild are reproducible with a small plerocercoid implanted into a large mature fish, which precludes pressure effects on fish organs or general debilitation from parasite metabolic demands Arme Fish used for hormonal or molecular biological analysis were examined within 7 days of capture.

Kerr and Arme noted that in ligulosed roach, Rutilus rutilusthe putative gonadotrophs are much reduced in number, compared with non-ligulosed individuals, are only lightly granulated, inteztinalis have an irregular nuclear lifula, no prominent nucleolus and a marked reduction in the cytoplasmic volume.