Epidemiology and taxonomy of Diplostomum species (Trematoda: Diplostomatidae) infecting fish of Llyn Tegid, North Wales and the Ruvu Basin, Tanzania.
This study investigated the epidemiology and taxonomy of Diplostomuni
species in the deeper parts of the eye (DPE) of roach Rutilus rutilus (L. ),
perch Perca fluviatilis L., ruffe Gymnocephalus cernua (L. ) and gwyniad
Coregonus lavaretus (L. ) at Llyn Tegid, North Wales, and in the cranium of
catfish Clarias gariepinus (Burchell, 1822) and the vitreous humour of
Oreochromis species at Mindu dam and river Ruvu, Tanzania.
At Llyn Tegid, two species of Diplostomum metacercariae, large and
small forms, coexisted in DPE of perch, ruffe and gwyniad but only one,
large forms, occurred in roach. Large forms were distinguished by their
large size, oval body tapering at both ends and pseudosuckers at the level of
the oral sucker. Small forms were distinguished by their smaller size, oval
body with parallel sides and pseudosuckers occurring below the level of the
oral sucker. The taxonomy of the two forms was not resolved even after
obtaining adults from chickens. Tentatively, small forms keyed close to D.
gasterostei Williams, 1966 and large forms to D. volvens Nordmann, 1832.
Inadequate identification manuals and remarkable similarity between
Diplostonlum species confounded identification.
Mean intensity of metacercariae was highest in ruffe and lowest in
perch and increased with host size in all hosts. Factors responsible for
differences in mean intensity between hosts were discussed. There was no
seasonality of occurrence. Recruitment occurred from May - November
correlating with water temperatures. Immature metacercariae occurred
throughout the period of investigation. Metacercariae were overdispersed
in all three hosts.
At Mindu and Ruvu two species were present, D. sp. X (1,2) in the
cranium of catfish and D. sp. Y in the vitreous humour of Oreochromis sp.
D. sp. X (1,2) were distinguished by their elongate body, oval calcareous
corpuscles and long hindbody. D. sp. Y were distinguished by a vestigial
ventral sucker, glandular Brandes organ, short hindbody and spherical
calcareous corpuscles. D. sp. X (1,2) were identified as D. mashonense
Beverley - Burton, 1963. Adults cultured in chickens confirmed
identification. D. sp. X (1,2) developed to ovigerous adults within 24h.
Percent recovery of adults from chickens declined with days p. i. Miracidia
developed in eggs in six days. D. sp. Y is considered an undescribed taxon.
Prevalence and mean intensity of D. sp. Y in Oreochromis sp. were low
and did not fluctuate seasonally. Prevalence of D. mashonense in catfish
was similar at Mindu and Ruvu and exhibited no seasonal fluctuations.
Mean intensity of D. mashonense in catfish of Mindu fluctuated seasonally,
increased with host size and was higher than in catfish from Ruvu. Causes
of high intensity and seasonal changes at Mindu were discussed. D.
mashonense was overdispersed in catfish at both localities but only data
from Mindu fitted the negative binomial model. Small samples and the
dynamism of forces creating overdispersion were considered responsible
for the situation at Ruvu.
Using SEM ciliated-pit and dome-shaped papillae were observed on the
surface of metacercariae and adults of D. mashonense .
occurred only on metacercariae. Dome-shaped papillae, in adults and
metacercariae, were aggregated on suckers, excretory and genital atria.
Spines were multipointed in adults but single pointed in metacercariae.