Ultrastructural and genetic diversity studies of two Sclerocollum (Acanthocephala) species infecting Siganid and Lutianid fishes from the Red Sea, Egypt.

Little is known about the distribution of Acanthocephala in local waters. A survey was carried out on the commercially important herbivorous Siganid fish, Siganus rivulatus and S. luridus, as well as Lutianid fish Centropristisfilamentosus inhabiting the Red Sea to determine the prevalence of Acanthocephala parasites. One hundred and thirteen fish were examined. The infection rates of S. rivulatus and S. luridus with Sclerocollum rubrimaris Schmidt and Paperna 1978 (Rhadinorhynchidae: Gorgorhynchinae) were 59 % & 33%, respectively. Meanwhile, 59% of C. filamentosus were found infected by Sclerocollum sp. The abundance, host-parasite relationships and microhabitat of S. rubrimaris were investigated and discussed. SEM was the employed to investigate the differences between the two species of Sclerocollum. For accurate estimation of genetic diversity of these species, randomly amplified polymorphic DNA (RAPD) genomic fingerprinting was proposed, using four different random primers. SEM studies showed that the two examined species differ in the length of proboscis hooks, the number of longitudinal rows of hooks on proboscis, distance between the bases of hooks and in egg size. The trunk surface of Sclerocollum sp. had minute, scale-like spines that were arranged in oblique lines whereas the trunk surface of S. rubrimaris had small pores and sclerotised plates on its anterior portion. RAPD primers revealed 52 amplification products and species-specific markers were identified. The deduced phenogram comprised two main clusters each includes one of the examined Sclerocollum species. Results indicated that RAPD markers are useful for the assessment of genetic diversity between the investigated Sclerocollum species which concur with SEM outcome.