Studies on the life cycle of the pseudophyllidean cestode Schistocephalus solidus

Abstract

Summary A study of host‐parasite relationships has been made on the cestode Schistocephalus solidus Müller by examining conditions relating to the infection and growth of the plerocercoid in the stickleback, and‐ its transfer to other hosts for maturation; the infection of Cyclops by the coracidimn with its subsequent change to a procercoid; and the passage of the procercoid into the body cavity of the fish to become a plerocercoid. It has been possible, by establishing suitable techniques, to carry out the whole life cycle in the laboratory and so facilitate these studies. Eggs were obtained from plerocercoids and observations made on their development. The time of hatching of the coracidium varies considerably, both with temperature and with intrinsic factors. The average time is about three weeks but hatching may occur up to six months after the eggs have been shed. From such eggs, free coracidia and, subsequently, procercoids in Cyclops and nauplii, were secured and studied. The growth rate of procercoids was determined together with the effect of infection on the growth of nauplii. Infections in fish were secured from infected Cyclops but not in sufficient numbers to justify more than tentative conclusions about the growth rate of plerocercoids. The time required for penetration of the fish gut wall by the procercoid can be as short as two hours. Changes in morphology of the worm in its transformation from a coracidium to a plerocercoid were surveyed and it was shown how the formation of the musculature precedes the initiation of strobilation which occurs rapidly and completely, followed immediately by the formation of the genital rudiments. The excretory system of the plerocercoid could be displayed effectively by a method of embedding in transparent plastic. Infected fish from one source were collected throughout the year and the weights of the fish and of the worms within them were ascertained. It was found that in the autumn there was an increase in the number of large fish in the marginal zone–possibly related to an increase of plankton–but during the months from winter to summer the mean size of fish was less and remained relatively stable in this zone. The mean weights of plerocercoids however, increased during this period as did the temperature of the water. Some indications of the growth rate of the plerocercoid were observed from the collected data. An examination of the stomach contents of the fish showed a wide variety of diet with little or no change throughout the year and also indicated that Cyclops form an almost insignificant feature in this diet.

Infection patterns of Nile tilapia (Oreochromis niloticus L.) by two helminth species with contrasting life styles

“…Moreover, receding water again inhibits coracidia hatching, resulting in a low population of infective stages after rains. Although temperature is also an important abiotic factor triggering cestode hatching (Clarke 1954;Scholz et al 2004) as well as increasing intake of intermediate hosts by fish (Hanzelova and Gerdeaux 2003;Wicht et al 2009), the present study could not ascertain the magnitude of the contribution.…”

The three-spined stickleback-Schistocephalus solidussystem: an experimental model for investigating host-parasite interactions in fish

“…34 We begin our review with background information on the parasite's lifecycle, on the host fish 35 and the 'typical' phenotype of infected sticklebacks in nature, and briefly discuss emerging 36 variation in infection phenotype. We then examine how aspects of the life cycle can be 37 experimentally manipulated in the lab to allow experimental infections of sticklebacks to be host (Clarke, 1954). 61 The geographical distribution of the parasite is limited by the distribution of the only obligate 62 host in the life cycle, the three-spined stickleback, which is restricted to the Northern 63 hemisphere and occurs around the margins of the Atlantic and Pacific Oceans (Bell and 64 Foster, 1994).…”

Can the behaviour of threespine stickleback parasitized with Schistocephalus solidus be replicated by manipulating host physiology?

“…Finally, another hypothesis that could explain some of the behavioural changes triggered by S. solidus infections has not yet been addressed; the possibility that the physical presence of a large parasitic mass inside the host is able to change host behaviour. Indeed, S. solidus can reach the same size as the host, and the parasite:host mass ratio can reach up to 94% (Clarke, 1954). Increase in parasite mass and the impact of this mass on internal organs could also be a cause of behaviour changes.…”

“…During this growth phase, the parasite shifts from being non-infective to attaining infectivity, when it is able to successfully establish and reproduce in its final host (Tierney and Crompton, 1992). The parasite life cycle is completed when a stickleback harbouring an infective worm is ingested by a suitable definitive host, typically a fish-eating bird or other endothermic vertebrate (Clarke, 1954). A suite of behaviours is changed in sticklebacks harbouring at least one parasite in the infective stage, forming a behavioural syndrome (Sih et al, 2004;Poulin, 2013).…”