Memórias do Instituto Oswaldo Cruz Fundação Oswaldo Cruz, Fiocruz ISSN: 1678-8060 EISSN: 1678-8060 Vol. 90, Num. 3, 1995, pp. 341-344

RESEARCH NOTE

Metacercariae of Diplostomum (Austrodiplostomum) compactum (Trematoda, Diplostomidae) in the Eyes of Plagioscion squamosissimus (Teleostei, Sciaenidae) from the Reservoir of the Hydroelectric Power Station of Itaipu, Brazil

Anna Kohn+, Berenice MM Fernandes+ , Maria de Fatima D Baptista-Farias

Laboratorio de Helmintos Parasitos de Peixes, Depaflamento de Helmintologia, Instituto Oswaldo Cruz, Av. Brasil 4365, 21045- 900 Rio de Janeiro, RJ, Brasil

Code Number: OC95067
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From 32 different species of fish examined from the reservoir of the Hydroelectric Power Station of Itaipu, Parana River, southern Brazil, during 15 days expeditions in the years of 1991, 1992 and 1993, only Plagioscion squamosissimus (Heckel) presented the eyes infected by metacercariae of a species of the genus Diplostomum. All the 17 specimens of P. squamosissimus examined were parasitised by about 2 to 100 worms/eye free (unencysted) in the vitreous humour. The methodology used was described in A Kohn et al. (1994 Syst Parasit 27: 127-132.

A Lutz (1928 Estudios de Zoologia y Parasitologia Venezolanas, 133 pp.) described a parasite of Carbo brasiliensis from Venezuela as Alaria compacta. L Szidat and A Nani (1951 Rev Inst Nac Cienc Nat Bernardino Rivadavia 1: 323-384) described Diplostomulum mordax from the brains of Basilichthys microlepidotus and the adult Austrodiplostomum mordax from Phalacro- corax olivaceus, from Argentina. (3 Dubois (1970 Mem Inst Oswaldo Cruz 68: 169-196) named Alaria compacta as Diplostomum (Austrodiplostomum) compactum and considered A. mordax as its junior synonym.

M Ostrowski de Nunez, in 1964 (Neotropica 10: 114-119) and 1968 (Neotropica 14: 85-88) studied the biology and life history of A. mordax and later, in 1977 (Rev Mus Arg Cienc Nat Bernardino Rivadavia 2: 1-63) published an extensive paper on this species, considering it also a junior synonym of D.(A.) compactum.

In 1982 (Zool Anz 208: 393-404), this author elucidated the life history of D.(A.) compactum in Lake Valencia, Venezuela, and recognized it and D.(A.) mordax, from Argentina, as different species.

Our specimens fit the description of the metacercariae of D.(A.) compactum described by M Ostrowski de Nunez (1982 loc. cit.)from Geophagus sp. from Venezuela.

Description was based on 24 specimens studied under light microscopy and two under SEM. Measurements of 14 compressed worms are given in mm followed by the mean in parenthesis. The metacercariae of D.(A.) compactum present a foliaceous body ventrally concave, with small conical posterior segment (Figs 1-3). Body 1.47-2.74 (2.17) long, 0.60-1.18 (0.97) wide. Anterior region with small subterminal oral sucker, is 0.041- 0.097 (0.077) long by 0.056O. 116 (0.079) wide, and has two lateral, well developed pseudo-suckers (Figs 2-4). The surface of the worm is finely ridged, with cobblestonelike tegument (Figs 5-6). Small and thiny spines are present on the surface of the tegument, only visible by SEM at higher magnification, more evident at the anterior region of body (Fig. 4) and around the holdfast (Fig. 5). Dome-shaped nonciliated papilae, irregularly distributed on body surface (Fig. 6, arrows). Pharynx oval, 0.0640.094 (0.083) long by 0.045-0.079 (0.060) wide. Oesophagus shot't. Intestinal caeca ending blindly near posterior extremity. Ventral sucker absent. Holdfast (tribocytic organ) oval, well developed, located in posterior third of body (Figs 1-3); measures 0.326-0.650 (0.507) long by 0.2510.500 (0.370) wide. Gland cells filling most parts of body anterior to tribocytic organ. Gonads small, situated in posterior region of body (Fig. 1).

Measurements of eight non compressed worms: total body length 1.03-1.35 (1.19) by 0.47-0.85 (0.63) wide, oral sucker 0.049- 0.082 long by 0.049-0.067 wide, pharynx 0.049-0.079 long by 0.019-0.056 wide, tribocytic organ 0.260-0,390 long by 0.112- 0.300 wide.

Metacercariae of Diplostot. num spp. parasitize

Metacercaria of Diplostotnum (Austrodiplostomum) cotnpactum (Lutz 1928) -

Fig. 1: whole mount, ventral view. Scale = 0.5mm.

Figs 2- 3: scanning electron micrographs, ventral views, showing different aspects of body shape. Bar = 0.2 min.

Scanning electron micrographs of the tegument of metacercaria of D. (A.) compactum.

Fig. 4: anterior end of body with anterior sucker and lateral pseudo-suckers, showing small and tinny spines of the tegument. Bar = 0.05mm.

Fig. 5: ventral surface of posterior region of body, showing holdfast (tribocytic organ) and finely ridged tegument with spines Bar = 0.03 min.

Fig. 6: higher magnification of body stuface showing cobblestone-like tegument and dome shaped non-ciliated papillae (arrows). Bar=0.01mm.

Acknowledgements: to the "Superintendencia de Meio Ambiente Aquatico" and "Centro de Pesquisas, Itaipu Binacional" for the facilities offered to examine the fishes from the reservoir of the Hydroelectric Power Station. To Dr Wanderley de Souza (Instituto de Biofisica, UFRJ) for scanning electron microscopy facilities.

Copyright 1995 Fundacao Oswaldo Cruz

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