The attachment of cercariae of an ectoparasitic digenean,Transversotrema patialensis, to the fish host: behavioural and ultrastructural aspects

Abstract

The behaviour which enables the cercariae of the ectoparasitic digenean,Transversotrema patialensis, to establish themselves on the surface of their fish hosts has been described experimentally using anaesthetized fish. Specialized regions of the cercarial tail, the arm processes, seem to be adapted for both specific recognition of, and rapid attachment to, the outer surface of a fish. Each arm process bears an array of nine ciliary sensory structures, the mammiform receptors, which have been tentatively identified as contact chemoreceptor organs involved in host recognition. Also present on each arm is an adhesive pad that mediates the initial attachment to the host. It is a differentiated region of the distal cytoplasm of the epidermal syncytium which invests the whole arm process. The cytoplasm of the pad region contains membrane-bounded adhesive granules, the contents of which are released during activation of the pad.

Experimental investigations on the behaviour of the cercariae of an ectoparasitic digenean transversotrema patialense: general activity patterns

“…Snails (Melanoides tvberculata) infected with T. patialense were maintained in the laboratory as described by Anderson & Whitfield (1975). Freshly-shed cercariae were usually obtained by placing infected snails in tap water at 26 °C in the dark.…”

“…The proportion of time spent by the cercariae in spontaneous, unstimulated motion (swimming plus dropping) was found to be markedly agedependent. The proportion declined appreciably as cercariae aged and reached zero many hours before the cercariae finally died (Anderson & Whitfield, 1975).…”

“…some of the factors which give rise to the age-dependent infectivity of the larvae (Anderson, Whitfield & Mills, 1977). * We are deeply indebted to Professor H. Crusz for pointing out to us that the name Transversotrema patialensis utilized by us in previous publications (Anderson & Whitfield, 1975;Whitfield, Anderson & Moloney, 1975) as well as by other workers, is in fact invalid. The correct nomenclature is the one used in the present publication, namely Transversotrema patialense (see Crusz, Ratnayake & Sathananthan, 1964).…”

“…Recently, the aquatic locomotory behaviour of Transversotrema patialense cercariae has been described in outline with reference to the attachment of the cercariae to their fish final hosts (Whitfield, Anderson & Moloney, 1975). The large, furcocerous larvae were shown to divide their activities, in the period before attachment to a fish or death, into three different behavioural modes.…”

Swimming behaviour of the cercaria ofTransversotrema patialense

“…Experiments were conducted with the cercaria of Transversotrema patialense. The survival , attachment behaviour (Whitfield, Anderson & Moloney, 1975), activity (Whitfield, Anderson & Bundy, 1977) and infectivity (Anderson, Whitfield & Dobson, 1978) of this cercaria have been described. Some qualitative information on swimming characteristics is known and the morphology of the cercaria has been described (Whitfield et al 1975).…”