Influence ofLigula intestinalisplerocercoids (Cestoda: Diphyllobothriidea) on the occurrence of eyeflukes in roach (Rutilus rutilus) from a lake in south-east England

Abstract

Vertebrate hosts commonly harbour concurrent infections of different helminth species which may interact with each other in a synergistic, antagonistic or negligible manner. Direct interactions between helminths that share a common site in the host have been regularly reported, but indirect interactions between species that occur in different sites are rarely described, especially in fish hosts. Plerocercoids of Ligula intestinalis are common infections of the peritoneal (body) cavity of roach (Rutilus rutilus) in freshwater habitats. These larval cestodes can cause extensive systemic pathologies to the fish host, which in turn may alter its susceptibility as a target host for other helminth species. The present study, using an existing dataset, investigates the influence of L. intestinalis (ligulosis) on frequently occurring eyefluke infections in roach sampled from a lake in south-east England. The occurrence of two species of eyefluke (Diplostomum sp. and Tylodelphys sp.) in the roach population demonstrated no significant levels of interaction with each other. The prevalence but not mean intensity or abundance of Diplostomum sp. was significantly increased in ligulosed roach, while the incidence of Tylodelphys sp. remained unchanged. Analyses of bilateral asymmetry in the occurrence of eyeflukes in left and right eyes of infected fish demonstrate that Tylodelphys sp. shows significant asymmetry in non-ligulosed roach, which is not replicated in ligulosed individuals. In contrast, Diplostomum sp. shows no evidence of asymmetry in either ligulosed or non-ligulosed fish.

Influence of an extreme climatic event on bilateral asymmetry and occurrence of eye flukes in perch (Perca fluviatilis) and roach (Rutilus rutilus) from a lake in southeast England

“…Such asymmetry appears to be influenced by stressful conditions either of a biological (e.g. Morley & Lewis, 2019) or of an environmental origin, such as extreme climatic events highlighted in the present study, and these factors may explain the high levels of inconsistency in its occurrence reported by previous studies. Fluctuating asymmetry of fish has been widely promoted as a useful bioindicator of exogenous stressors in a range of habitats (Allenbach, 2011) whereas parasites have also been suggested as valuable indicators of environmental degradation (Vidal-Martinez et al ., 2010).…”

“…In addition, the body cavity of roach was also examined for the larval cestode L. intestinalis as Morley & Lewis (2019) established that this cestode species can influence the presentation of bilateral asymmetry in eye flukes. In each year a small number of sampled fish were infected with L. intestinalis (1993 n = 23, 1994 n = 11, 1995 n = 3, 1996 n = 2).…”

“…The majority of previous studies have examined eye fluke asymmetry in the lenses of fish with only a limited number examining the distribution of metacercariae in the vitreous humour (Wayland & Chubb, 2016; Morley & Lewis, 2019). Similarly, comparative studies on the extent of asymmetry by different metacercarial species in the same host population are also few (Wayland & Chubb, 2016; Morley & Lewis, 2019).…”

“…The majority of previous studies have examined eye fluke asymmetry in the lenses of fish with only a limited number examining the distribution of metacercariae in the vitreous humour (Wayland & Chubb, 2016; Morley & Lewis, 2019). Similarly, comparative studies on the extent of asymmetry by different metacercarial species in the same host population are also few (Wayland & Chubb, 2016; Morley & Lewis, 2019). Factors that may moderate the development of bilateral asymmetry in fish are poorly known although Morley & Lewis (2019) demonstrated that concurrent infections with the larval cestode Ligula intestinalis could influence the symmetrical distribution of one species of eye fluke but not another in a population of roach ( Rultilus rutilus ) in southeast England.…”

“…Morley & Lewis (2019) showed that biotic stress induced by concurrent infections of L. intestinalis can influence the presentation of eye fluke bilateral asymmetry in freshwater fish populations, but the influence of abiotic stress due to environmental factors remains unknown. In the present investigation, using an existing dataset, eye fluke infections in two fish species are described from a lake in southeast England from 1993 to 1996.…”