Acta Parasitologica, Vol. 52, No. 3, 2007, 278285. DOI: 10.2478/s11686-007-0030-3 Reda M. El-S. Hassanine (1)* and Mohammed O. Al-Jahdali (2)
Ecological comments on the intestinal helminths of the rabbitfish Siganus rivulatus (Teleostei, Siganidae) from the northern Red Sea
(1) Department of Sciences and Mathematics, New Valley-Faculty of Education, Assiut University, El-Kharga, New Valley, Egypt;
(2) Sciences Department, Jeddah Teacher's College, Saudi Arabia
*Corresponding author: Redaaa2003@yahoo.com
Between May and September 2006, 640 specimens of the rabbitfish Siganus rivulatus Forsskål (Teleostei, Siganidae) were
examined for infections with intestinal helminths. These fishes were caught in the Red Sea off the coast of Sharm El-Sheikh,
South Sinai, Egypt, examined in a field laboratory and separated into three size groups of regular length intervals. Only three
species of helminths were recovered: the trematode Gyliauchen volubilis Nagaty, 1956 (Gyliauchenidae Fukui, 1929), the acanthocephalan
Sclerocollum rubrimaris Schmidt et Paperna, 1978 (Cavisomidae Meyer, 1932) and the nematode Procamallanus
elatensis Fusco et Overstreet, 1979 (Cucullanidae Cobbold, 1864). The distribution of these helminths along the intestine of
S. rivulatus, in all patterns of single and concurrent infections and the corresponding prevalences and intensities of infection
in the different size groups of the fish were recorded. In single infections, each parasite species was found distributed in a welldefined
fundamental niche along the intestine of Siganus rivulatus, and a distinct partial overlap between the niches of G. volubilis
and Sclerocollum rubrimaris was observed. In concurrent infections with these two species, their fundamental niches were
significantly reduced, probably being affected by interactive site segregation and individuals of each species were found segregated
in a restricted realised niche. In all other patterns of concurrent infections, each parasite species was normally found
in its original fundamental niche. The prevalences of these parasites in the fish examined were relatively low and somewhat similar.
In all patterns of single and concurrent infections, the intensity of infection was directly related to fish size. In concurrent
infection with G. volubilis and S. rubrimaris, a significant decline was observed in the intensities of both species in the different
size groups of the fish, but, in all other patterns of concurrent infections, no significant change in intensity was observed.
These observations suggest that the interaction between G. volubilis and S. rubrimaris is probably a negative and symmetrical
one. The mode of transmission of these parasites to the fish is also discussed.
Intestinal helminths, interactive site segregation, fish, Siganus rivulatus, Red Sea