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Occurrence of larval stages of Tylocephalum (Cestoda: Lecanicephaloidea) in two oyster species from northern Australia
JOURNAL
OF INVERTEBRATE
PATHOLOGY
27, 129-131
(1976)
NOTES Occurrence of Larval Stages of Ty/ocepha/um (Cestoda : Lecanicephaloidea) in Two Oyster Species From
Northern
The occurrence of coracidia and metacestodes of the lecanicephaloid cestode Tylocephalum sp. in the American oyster, Crassostrea virginica, has been established by A. K. Sparks (J. Invertebr. Pathol. 5, 284-288, 1963) and T. C. Cheng (Trans. Amer. Microsc. Sot. 85, 246-255, 1966), who examined a range of host specimens from Hawaii and Apalachicola Bay, Florida. The examination of 249 specimens of the Sydney rock oyster, C. commercialis, from northern New South Wales and southern Queensland, Australia, revealed the presence of coracidia in the labial palp region as well as infections of varying intensities and stages of encapsulation in the regions of the digestive diverticula in 95 specimens (36.5%). Furthermore, two specimens of the native oyster, C. echinata, among 11 collected (18%) in different areas of the Northern Territory were also found to be infected. The present discovery represents the first record of these larval parasites from Australia. In spite of extensive histological investigations by T. C. Roughley (Proc. Linn. Sot. N.S. W. 51, 446-491, 1926) and the present author, which amount to about 2000 sectioned specimens, no larval stages of Tylocephalum have ever been found in C. commercialis from central and southern parts of the New South Wales coastline. It seems reasonable to assume, therefore, that this helminth requires tropical or at least subtropical conditions for its successful transmission. So far, it has never been recorded from latitudes higher than 30”. All oysters were fixed in Davidson’s fluid, embedded in Paraplast, and sectioned at 6-7 pm across the digestive diverticula. The sec-
Australia tions were stained with Harris’s hematoxylin and eosin and also with the periodic acidSchiff reaction to demonstrate the capsular fibers and thickened intercellular material of the encapsulation complex (T. C. Cheng and E. Rifkin, in “Diseases of Fishes and Shellfishes,” Spec. Publ. No. 5., Amer. Fisher. Sot., Washington, D.C.). The position of the larval cestodes in the Sydney rock oyster was in full accordance with previous observations by T. C. Cheng (lot. cit.) on infestations of the American oyster. Ciliated coracidia were found between the gills and also in the labial palps. The infestation by metacestodes in the digestive region was of varying intensity, and up to 20 capsules in various stages of resorption could be seen in one section of a host specimen. It seems obvious that such a dense invasion is likely to put great strain on the host’s ability to cope with encapsulation and resorption of the parasite, a fact best documented by the poor transparent and watery condition of all affected oysters examined. A subsequent count of all histologically examined oysters permitted the computation of the percentage of incidence presented in Table 1. It is noted that 16 (6.2%) of the oysters affected by Tylocephalum displayed the presence of an additional parasite, a haplosporidan already described by the present author (P. H. Wolf, J. Invertebr. Pathol. 19, 416-417,1972). T. C. Cheng (lot. cit.) has shown it to be most likely that the pearl oyster from Ceylon, Pinctada margaritijka, could well have been the original intermediate host for transmission of the cestode, which appears to have spread to Hawaiian waters by elas-
129 Copyright All rights
D 1976 by Academic Press, Inc. of reproduction in any form reserved.
130
FIG. phalum
KOTES
1. Cross in various
section of the digestive gland region stages of development and resorption
FIG. 2. Encapsulated PAS stain. x 300.
Tylocephalum
in Crassostrea
of Crassosfrea commercialis (arrows). PAS stain. x 50.
commercialis
showing
host
showing
reaction
encapsulated
in connective
Tyloce-
tissue
131
KOTES
Incidence of Infection of Crassostrea
Area Northern New South Wales Southern Queensland Northern Territory Total
commercialis
Species Crassostrea Crassostrea Crassostrea
TABLE 1 and Crassostrea echinata No. of examined oysters
commercialis commercialis echinata
mobranchs, from which all known adults of the parasite have been recovered. This assumption seems to be strengthened by the results of the present study and to explain the distributional pathway of the parasite to northern Australian waters. Considering the absence of larval stages of the cestode in oysters from colder regions, it can be postulated further that only warm water elasmobranches are likely to be the carriers of adult cestodes of this genus and thus
117 132 11 260
metacestodes
by Tylocephalum
Infected with Tylocephalum
%
23 70 2 95
19.7 53.0 18.2 36.5
responsible for a well-defined tropical to subtropical dispersal of larval parasites in molluscan host. PETER H. WOLF
New South Wales State Fisheries Scientific Section 211 Kent Street Sydney, 2000, Australia Received August 13,1974
OF INVERTEBRATE
PATHOLOGY
27, 129-131
(1976)
NOTES Occurrence of Larval Stages of Ty/ocepha/um (Cestoda : Lecanicephaloidea) in Two Oyster Species From
Northern
The occurrence of coracidia and metacestodes of the lecanicephaloid cestode Tylocephalum sp. in the American oyster, Crassostrea virginica, has been established by A. K. Sparks (J. Invertebr. Pathol. 5, 284-288, 1963) and T. C. Cheng (Trans. Amer. Microsc. Sot. 85, 246-255, 1966), who examined a range of host specimens from Hawaii and Apalachicola Bay, Florida. The examination of 249 specimens of the Sydney rock oyster, C. commercialis, from northern New South Wales and southern Queensland, Australia, revealed the presence of coracidia in the labial palp region as well as infections of varying intensities and stages of encapsulation in the regions of the digestive diverticula in 95 specimens (36.5%). Furthermore, two specimens of the native oyster, C. echinata, among 11 collected (18%) in different areas of the Northern Territory were also found to be infected. The present discovery represents the first record of these larval parasites from Australia. In spite of extensive histological investigations by T. C. Roughley (Proc. Linn. Sot. N.S. W. 51, 446-491, 1926) and the present author, which amount to about 2000 sectioned specimens, no larval stages of Tylocephalum have ever been found in C. commercialis from central and southern parts of the New South Wales coastline. It seems reasonable to assume, therefore, that this helminth requires tropical or at least subtropical conditions for its successful transmission. So far, it has never been recorded from latitudes higher than 30”. All oysters were fixed in Davidson’s fluid, embedded in Paraplast, and sectioned at 6-7 pm across the digestive diverticula. The sec-
Australia tions were stained with Harris’s hematoxylin and eosin and also with the periodic acidSchiff reaction to demonstrate the capsular fibers and thickened intercellular material of the encapsulation complex (T. C. Cheng and E. Rifkin, in “Diseases of Fishes and Shellfishes,” Spec. Publ. No. 5., Amer. Fisher. Sot., Washington, D.C.). The position of the larval cestodes in the Sydney rock oyster was in full accordance with previous observations by T. C. Cheng (lot. cit.) on infestations of the American oyster. Ciliated coracidia were found between the gills and also in the labial palps. The infestation by metacestodes in the digestive region was of varying intensity, and up to 20 capsules in various stages of resorption could be seen in one section of a host specimen. It seems obvious that such a dense invasion is likely to put great strain on the host’s ability to cope with encapsulation and resorption of the parasite, a fact best documented by the poor transparent and watery condition of all affected oysters examined. A subsequent count of all histologically examined oysters permitted the computation of the percentage of incidence presented in Table 1. It is noted that 16 (6.2%) of the oysters affected by Tylocephalum displayed the presence of an additional parasite, a haplosporidan already described by the present author (P. H. Wolf, J. Invertebr. Pathol. 19, 416-417,1972). T. C. Cheng (lot. cit.) has shown it to be most likely that the pearl oyster from Ceylon, Pinctada margaritijka, could well have been the original intermediate host for transmission of the cestode, which appears to have spread to Hawaiian waters by elas-
129 Copyright All rights
D 1976 by Academic Press, Inc. of reproduction in any form reserved.
130
FIG. phalum
KOTES
1. Cross in various
section of the digestive gland region stages of development and resorption
FIG. 2. Encapsulated PAS stain. x 300.
Tylocephalum
in Crassostrea
of Crassosfrea commercialis (arrows). PAS stain. x 50.
commercialis
showing
host
showing
reaction
encapsulated
in connective
Tyloce-
tissue
131
KOTES
Incidence of Infection of Crassostrea
Area Northern New South Wales Southern Queensland Northern Territory Total
commercialis
Species Crassostrea Crassostrea Crassostrea
TABLE 1 and Crassostrea echinata No. of examined oysters
commercialis commercialis echinata
mobranchs, from which all known adults of the parasite have been recovered. This assumption seems to be strengthened by the results of the present study and to explain the distributional pathway of the parasite to northern Australian waters. Considering the absence of larval stages of the cestode in oysters from colder regions, it can be postulated further that only warm water elasmobranches are likely to be the carriers of adult cestodes of this genus and thus
117 132 11 260
metacestodes
by Tylocephalum
Infected with Tylocephalum
%
23 70 2 95
19.7 53.0 18.2 36.5
responsible for a well-defined tropical to subtropical dispersal of larval parasites in molluscan host. PETER H. WOLF
New South Wales State Fisheries Scientific Section 211 Kent Street Sydney, 2000, Australia Received August 13,1974