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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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, and have an irregular nuclear membrane, no prominent nucleolus and a marked reduction in the cytoplasmic volume. 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 without histological examination, the condition factor was calculated including the gonadal tissue in parasitised individuals.

In order to do this, fragments of the R. Detailed analysis of the spottail shiner-Ligula host-parasite system revealed that the number of plerocercoids differed between years and among habitats but there was no statistically significant seasonal pattern; recruitment of new worms was highest in young fish and decreased with age, and infected spottails had reduced gonad development.

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.

Fish used for hormonal or molecular biological analysis were examined within 7 days of capture. 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.

Results Parasite burden Details of fish used and effects of parasitism are shown in Table 1. Furthermore, in vertebrate hosts, Taenia taeniaeformis appears to directly affect the testis intestinslis the rat Lin et al.


Ligula intestinalis

Data were analysed using the Abi Prism sequence detection system Applied Biosystems. 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.

This appears to be related to the greater metabolic stress on infected males. 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. 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. Although this phenomenon has been reported several times e.

Plerocercoids were most prevalent 5. 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.

Because of the small amount of gonadal tissue in infected roach weighing less than 0. The gonads, however, are present but remain in an immature state, irrespective of fish age or season. Given that fish infected with Ligula intestinalis do not exhibit normal behaviour patterns in terms of shoaling e. Although individual variation was high, LH content of non-infected individuals was at its peak post-spawning August and lowest over the winter period December; Fig.

The fragments and nucleotides respectively obtained were cloned and sequenced Genbank accession numbers: Ligula intestinaliswhich is found in the body cavity of certain cyprinid fish, inhibits reproduction in both male and female fish. The reproductive system in fish is particularly susceptible to stress and immediate cessation of reproductive function is not uncommon when fish are brought into captivity Wendelaar Inhestinalis Introduction Intestinallis studies have revealed that several parasitic infections can affect host reproduction.

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

Ligula intestinalis could affect reproductive development of the fish at any level of the reproductive axis, from the first key hormones, gonadotrophin-releasing hormones GnRHto the gonads. 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. As has been noted previously by Inteatinalis et al. The condition factor assumes that heavier fish of a given length are in better condition and eliminates variation attributable to gonadal development over the reproductive season.


In contrast, in infected fish, only these immature stages of oogenesis were present throughout and no cyclical variations were recorded see Arme 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 of puberty noted in ligulosed fish.

However, seasonal variations in pituitary LH content observed in non-infected ligulq were absent in infected roach. Comparison of body mass to condition factor of ligulosed and non-ligulosed roach. 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.

Materials and methods Fish Ligulosed and non-ligulosed roach were collected from the Altami Angling Club, Chester, Cheshire, UK during — at three times during the reproductive year: Gonadal development Because of the small amount of gonadal tissue in infected roach weighing less than 0.

In this study, our objective was to establish whether gonadal inhibition induced by Ligula in its primary fish host, Rutilus rutilusis mediated through effects on pituitary gland hormone levels, i. Previous observations have revealed that two GnRH forms salmon and chicken occurred in the brain of non-infected and infected roach Williams et al. Table 1 Data summary for all experimental fish. 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.

GSI leading up to spawning February varied between 0. However, an apparently increased LH production in the eel suggested possible species differences in the action on gonadotroph activity. The sample size is shown above each bar.