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Taxonomic and biological studies of protozoan parasites in Tasmanian marine fishes

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Su, XQ (1993) Taxonomic and biological studies of protozoan parasites in Tasmanian marine fishes. PhD thesis, University of Tasmania.

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Abstract

Twelve species of marine fish were sampled over a 22 month period from Dru Point,
North-West Bay, south-east of Hobart, Tasmania, Australia, to investigate the protozoan
parasites present on the external surface and in the internal organs of fish. A total of 16
species of protozoan parasites belonging to 11 genera (in addition to the collective group
Microsporidium), 10 families and 4 phyla were obtained. Among these, 12 new species
are described. Two new Australian records and two unidentified forms are reported.
Detailed ultrastructural studies were carried out for Zschokkella leptatherinae sp. nov., a
myxosporean from the hepatic ducts of the atherinid fish, Leptatherina presbyteroides.
The development of Z. leptatherinae can be described by four stages: pansporoblast
formation, capsulogenesis, valvogenisis and sporoplasm maturation. The formation of
the early pansporoblast of Z. leptatherinae is by the union of two generative cells. Two
spores are produced from one pansporoblast at the end of sporogenesis.
The surface topography and the adhesive discs of Paratrichodina tasmaniensis sp. nov.
from the gills of two species of atherinid fish Leptatherina presbyteroides, Atherinosoma
microstoma and Trichodina nesogobii from the gills of gobio, Nesogobius sp.1 were
examined using scanning electron microscopy. Both ciliates have two ciliary bands
around the body surface. The adoral ciliary spiral turns 150-2000 in P. tasmaniensis,
while it is about 370-4000 in T. nesogobii. The aboral ciliary band consists of three
distinct sets of cilia in both species; however the length of the cilia, as well as the
development of the septum which separates each set of cilia, are different. The adhesive
disc of T. nesogobii shows a similar structure as observed by the light microscope. An
ellipsoidal foramen is visible clearly in the denticle of P. tasmaniensis which
corresponds to a small dot in silver impregnated specimens.
Ecological studies were conducted on Zschokkella leptatherinae and Paratrichodina
tasmaniensis and their two host species, Atherinosoma microstoma and Leptatherina
presbyteroides. The frequency distributions, the seasonal variations of parasite infection
as well as the relationships between the parasites and the host fishes were investigated.
The frequency distribution of Z. leptatherinae in both fish species and P. tasmaniensis in L. presbyteroide fit the log-normal distribution model. The infection of Z. leptatherinae
showed no significantly seasonal variation, while a pronounced seasonal variation was
revealed in the infestation of P. tasmaniensis. The prevalence and intensity of infestation
were high in summer and spring, low in winter and autumn in both Atherinosoma microstoma and Leptatherina presbyteroides. Infection of Z. leptatherinae occurred more
frequently in larger hosts in both fish species. For P. tasmaniensis, the variation of
infestation in different size group was closely related to the seasonal variations of
infection. There were no significant differences in the prevalence of infection of both
parasite species between the male and female samples of A. microstoma and L.
presbyteroides.
The interspecific associations between six species of protozoan parasites and the spatial
distributions of Paratrichodina tasmaniensis on the gills of host fish were also analysed.
A positive association was found between P. tasmaniensis and Trichodina australis in A.
microstoma. A negative association existed between T. australis and Zschokkella
leptatherinae, Trichodina sp. and Z. leptatherinae in A. microstoma; P. tasmaniensis'and
Z. leptatherinae, Clausophrya branchialis and Z. leptatherinae in L. presbyteroides. A
preliminary investigation revealed that P. tasmaniensis has a significantly high affinity for
the left gill arches in both A. microstoma and L. presbyteroides.
Both Zschokkella leptatherinae and Paratrichodina tasmaniensis_are pathogenic agents of
atherinid fishes. The liver of L. presbyteroides infected by Z. leptatherinae shows clear
histopathological change. Proliferation, enlargement and thickening of the hepatic ducts
are observed. The epithelial cells of infected fish are lower than the normal cells. The
parasites also provoke blockage of the hepatic ducts and atrophy of the neighbouring liver
parenchyma. In more advanced infection, over 85% of the liver tissue is replaced by the
plasmodia; and necrosis occurs finally.
The gills of Atherinosoma microstoma infested by Paratrichodina tasmaniensis show
sloughing of the epithelial cells of secondary lamellae, hyperplasia of interlamellar and
secondary lamellar epithelial cells and fusion of the adjacent secondary lamellae. Using
the transmission electron microscope, hypertrophy of the epithelial cells of secondary
lamellar is observed. The pillar cells are irregular and the basement membrane is thinner
than those in uninfested fishes. The pattern of surface ridges is often disrupted.

Item Type: Thesis (PhD)
Keywords: Marine fishes
Copyright Holders: The Author
Copyright Information:

Copyright 1993 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Includes bibliographical references (leaves 198-226). Thesis (Ph.D.)--University of Tasmania, 1994

Date Deposited: 04 Feb 2015 23:37
Last Modified: 19 Jun 2016 23:45
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