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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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.

In addition, we have for the first time revealed that the LH pituitary content and mRNA levels are also significantly decreased in intedtinalis individuals.

Data were analysed using the Abi Prism sequence detection system Applied Biosystems. Ligula infection could also affect LH production by acting directly on the gonadotrophs.

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

The latter has been demonstrated in other cyprinids where positive and negative responses have been noted for GnRH and dopamine respectively for review intestihalis Peter et al. It may intestjnalis 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. Previous observations have revealed that two GnRH forms salmon and chicken occurred in the brain of non-infected and infected roach Williams et al.

The fact that this inhibition was not observed when we compared older fish may arise from ligjla negative effect of sexual maturation on growth and condition e.

Infected fish have lower K values, reflecting a lower body growth lgiula. However, seasonal variations in pituitary LH content observed in non-infected fish were absent in infected roach. These studies have led to the belief that the effects of Ligula on gonadal development may be mediated through the pituitary gland.


Because of the small amount of gonadal tissue in infected roach weighing less than 0. Results Parasite burden Details of fish used and effects of parasitism are shown in Table 1. Effects of parasitism on host: For example, the expression of gonadotrophin hormones and their receptors e.

Details of fish used and effects of parasitism are shown in Table 1.

Transcript levels were normalised to those of 18S rRNA and data for infected fish presented as a fold change relative to the values obtained for non-infected fish. The reproductive system in fish is particularly susceptible to stress and immediate cessation of lgula function is not uncommon when fish are brought into captivity Wendelaar Bonga Our results have confirmed previous observations made by Armeon the biometric effects of Ligula intestinalis on its roach intermediate host.

Investigations of the effect of Ligula on the production of the other intfstinalis follicle-stimulating hormone are also required, especially considering the potential effect of the parasites on the early stages intestinslis gametogenesis. Indeed, sexual maturation will occur every year in non-infected fish but not in infected ones.

However, seasonal variations in GnRH cell activity in non-infected fish were not investigated, and it cannot therefore be deduced that GnRH cells or GnRH release are not affected in infected fish. Based on increased mean somatic weight and skewness of the weight distribution for infected fish, we propose that infected spottails inteztinalis subjected to size-selective mortality.

Fish exceeding 20 g were not infected with Ligula. Analysis of host and parasite growth revealed that the soma of male spottails infected with Ligula weighed more but had a reduced growth rate. This appears to be related to the greater metabolic stress on infected males.

Furthermore, in vertebrate hosts, Taenia taeniaeformis appears to directly affect the intestinalsi in the rat Lin et al. 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. Correlations between body parameters were subjected to regression analysis.


As an internal control, 18S rRNA was amplified in an identical manner.

Intestnalis6; Further quantification was performed in sections of the ovaries to determine the extent of oocyte development. Furthermore, peripheral stimulators and inhibitors, active at all levels of the brain—pituitary—gonadal BPG axis, may be targets of the putative hormonal disruption by Ligulawhich results in an inability of the gonads to respond to hormonal signals.

Ligula intestinalis

The distribution, cell number and staining intensity of both these types of neurones, which are considered to be the first steps in BPG axis activation, were not affected by Ligula Penlington et al. Introduction Previous studies have revealed that several parasitic infections can affect host reproduction. Whether this is mediated by direct effects of Ligula products or general endocrine disruption requires elucidation.

Figures given are means with range. 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. As in other vertebrates, body growth and condition have been suggested to act as triggers for the initiation of puberty in fish, although the mechanisms by which such a trigger is initiated is still largely unknown for reviews see Peter et al.

In contrast, in infected fish, only these immature stages of oogenesis were present throughout and no cyclical variations were recorded see Arme 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 following degenerate primers were used: