Taxonomy and biology of Diplozoidae (monogenea).
The study is divided into two parts. The first considers the
taxonomy of species of Diplozoidae in the British Isles and the world.
The second investigates the biology of Diplozoon homoion in field
and experimental conditions.
As a result of an extensive literature survey, the distribution
of species of Diplozoidae has been assessed. About 63 species were
found on 78 species of fishes of the families Cyprinidae and three
of Characidae. The species of parasites occurred in Asia, Europe
and Africa but not in Australia or North and South America. The
factors effecting this distribution were discussed.
Critical taxonomic studies on British materials revealed that
there are two species, D. paradoxum from Abramis brama distinguished
especially by an invagination and a few ridges (deep folds) on the
posterior parts of the adult stages, and, D. homoion from various
species of Cyprinidae, including A. brama, with an absence of these
two characters on the adults.
A study of the morphology of all stages in the life cycle of
D. homoion revealed that most of the characters currently used in
systematic work on Diplozoidae showed great variation and were therefore
unreliable. As a consequence, many species which have been described
are synonyms. Proposals made by other authors for new genera, subgenera
and subspecies of parasites are critically discussed with special reference to phylogeny. The genera Diplozoon, Eudiplozoon and Inusiatus
are thought to be valid. The genus Neodiplozoon requires further
investigation. All the other genera, subgenera and subspecies are
considered invalid. The Diplozoidae probably originated from both
Microcotylidae and Discocotylidae, with the genera Eudiplozoon and
Inusiatus ancestral to the other members of the family.
The life cycle of D. homoion from Llyn Tegid was studied
experimentally under laboratory conditions. At water temperatures
of 18o_21 oC, the life cycle took 1~-20 days from egg laying to formation
of the gravid worm.
The prevalence, relative density, mean intensity and intensity
of infection of Rutilus rutilus with D. homoion from Llyn Tegid were
investigated from September, 1982 to December, 1983 and in June and
July 1984. Infections were almost constant on all male, female and
unsexed fishes throughout the year. The level of infection of fishes
of different fork lengths was also investigated. Infections were
minimal in fishes less than 10 cm long, but increased progressively
with increasing lengths up to 20 cm but declined thereafter.
The distribution of adult D. hornoion on the gills of R. rutilus
from Llyn Tegid was also examined in relation toLserial number of
Qt.ft ht l
the gil¥; the side of the fish, tte inner and outer hernibranchs,
the segment of the gill and the manner of attachment of the clamps
to one or two consecutive primary lamellae. It was found that the
adult parasites were randomly distributed in relation to the gills'
structures except for a preference for attachment to the first 3
gills and to the dorsal segments of the gills. Two consecutive primary
lamellae were used for attachment twice as often as attachment to
a Single lamella. Season, sex and fork length of the fishes had no
effect on the distribution of the parasites on the gills