Both wild and farmed marine fish face a wide range of threats, including parasites that impair their health, growth, and survival. Such parasite-related threats cause economic losses to fish farmers  .
Among the parasites affecting fish health are parasitic crustaceans and monogenetic trematodes that cause severe destruction of fish gills, leading to anemia and death   . Multiple factors can alter the relationships between host fishes and their parasites     .
Monogenea and parasitic crustaceans (Isopoda and Copepda) as well as digenetic trematodes have been studied in various species of Scarus fish (Scaridae) worldwide.
Jones and Cabral  described Hatschekia manea (Copepoda) from the gills of Scarus gibbus in the South Pacific Ocean. The variability in the interactions between seven reef fish species (including Scarus sordidas) and their ectoparasitic fauna were studied by Alexandra  from Australia. Williams and Bunkly-Williams  recorded Nerocila california (Isopoda) from the external body surface and gills of Scarus compressus from the Eastern Pacific Ocean. Parasitic crustaceans, including praniza larvae of Gnathia sp. and Hatschekia leptoscari, were described and recorded by Toulah  and Bakhrebah  from Scarus ferrugineus from the Red Sea by Jeddah, Saudi Arabia. Morsy et al.  described Diplectanum harid (Monogenea) from the gills of the parrotfish Scarus harid from the Red Sea near Hurghada, Egypt. Kardousha  studied the helminth parasites of 51 marine fish species from the Arabian Gulf and referred to the infestation of the parrot fish Scarus gobban with digenetic trematoda and acanthocephala. Some of the ecto- and endoparasites of Scarus fish, (praniza larva, Hatshekia, Bucephalus and Lecithocladium spp.) were also recorded from other different fishes from the Red Sea coast of Jeddah city in Saudi Arabia    . Most of the previous mentioned studies were taxonomic.
The aim of the present investigation is to review the different types of metazoan parasites infesting two different species of Scarus fish (Family Scaridae) from the Red Sea coast of Saudi Arabia with special reference to their host-parasite relationship.
2. Materials and Methods
The present study was carried out on total number of 60 specimens of two different species of Scarid, parrot fish (Family Scaridae). Each species consisted of 30 fish of different sexes, one caught from Jeddah and the other from Rabigh cities at the Red Sea coast of Saudi Arabia.
Captured fishes were freshly brought to the laboratory and their sexes were determined. Skin surface, fins and gills were visually examined for any external parasites with the help of a dissecting microscope. Visceral organs of fish were slit open and their contents were collected in Peteri dishes then examined under a dissecting microscope. Copepoda and Isopoda were preserved in 10% buffered formalin and cleared with lactophenol. Trematodes were preserved in formalin-alcohol-acetic acid and stained with Semichons acetic carmine stain.
Statistical analyses were done by using Mann Whitney U test or student t-test. Significant level was at 0.05.
Parasitological examination revealed that Scarus fish under consideration harboured Monogenea, Isopoda and Copepoda on their gills and Digenea in their intestines. Table 1 represents the five species of parasites collected from the two different species of Scarus fish of Jeddah and Rabigh, their prevalences and mean intensities.
Diplectanum sp. from Scarus sp. of Rabigh was the most common parasite, followed by praniza larva from Scarus sp. of Jeddah, followed by Lecithoclaster sp. from Scarus sp. of Rabigh. Hatschekia and Bucephalus spp. were the minority. Generally Scarus fish species from Rabigh had higher prevalence and mean intensity of parasite than those from Jeddah. Monogenea and Digenea were not represented in Scarus fish from Jeddah as well as Copepoda in Scarus fish from Rabigh. Difference in the prevalence of infestations and parasite intensities for
Table 1. Prevalence (%) and intensity (M ± S.E.) of different parasites infesting the two Scarus fish species from Jeddah and Rabigh.
each fish species in the two different localities was not significant (significant value = 0.651).
All female Scarus fish of Jeddah were not infested. Males of the same species were infested with praniza larva of Gnathia sp. and Hatschekia sp. with overall prevalence (65%) and mean intensity 6.92 (Table 2). Male Scarus fish from Rabigh were infested with only one parasite species, Diplectanum sp. (prevalence 27.3% and mean intensity 19) while females showed higher prevalence and lower intensity of monogenetic infestation than male fishes and were infested with four parasite species, with overall prevalence and mean intensity of parasite (84.2%) and (6.43) respectively (Table 3).
Statistical analysis showed significant difference in the prevalence and mean intensity of parasite between female and male fish (Significant value = 0.029).
The present study, up to our knowledge, is the first done in Saudi Arabia Red Sea coast (Jeddah and Rabigh) to show the parasitic fauna (type and number of species and degree of parasitic infestation in relation to some factors) in two species of Scarus fish.
Distinct variation in composition of the parasitic fauna was noted in the two different localities. In Jeddah, Scarus fish was infested with parasitic Crustacea on their gills (Isopoda and Copepoda) while in Rabigh it was infested with Trematoda (Monogenea on their gills and Digenea in their intestines). Bauer  and Ramadan and Shakweer  reported that the type and rate of parasitic infestation in fishes depend on ecological and hydrobiological conditions of water. Barse  investigated the prevalence and intensities of gill parasites of Fundulus heteroclitus from two creeks different in salinity. He found that parasite densities were greater in the less saline creek for all collected parasite taxa.
Host specificity phenomenon was well established in this work where Monogenea, Diplectanum sp. showed the highest prevalence and mean parasitic intensity
Table 2. comparison of prevalence (%) and intensity (M ± S.E.) of different parasites infecting female and male examined Scarus fish in Jeddah.
Table 3. comparison of prevalence (%) and intensity (M ± S.E.) of different parasites infecting female and male examined Scarus fish in Red Sea of Rabigh.
and was collected from the gills of Scarus sp. of fish from Rabigh only. This was lined up with Llewllyn  , Rhode  and Whittington et al.  . They reported that most of the Monogenean gill parasite was found to be strictly specific to particular host. Llewllyn  proved that there was an exacting topographical relationship between a parasite and its host and this was probably an important factor in the mechanism of host specificity.
Praniza larva infested the two Scarus sp. with lower prevalence and intensity of parasites than Diplectanum sp. According to Sasal et al.  Diplectanum sp. could be classified as a specialist parasite of fish species (found only in one species) and Praniza larva as generalist (found in two or many host species).
In Rabigh, a statistically significant finding was observed where the female fish of Scarus sp. was infested with four parasite species while male fish had only one species (Diplectanum sp.). Prevalence of Monogenetic and overall parasite infestation was higher in female than male fishes, but the reverse was seen in the mean intensity. These findings may be due to mode of life, physiological and behavioral characters of each sex. Another interesting finding was found in Jeddah where no female fish showed any infestation as opposed to male that showed infestation with only parasitic crustacea (Isopoda and Copepoda). Our findings are different to Khalil  , Barse  , Adou et al.  and Aydogdu et al.  who found no definite difference in the prevalence and intensity of parasitic infestation according to fish sex.
In summary, this study identifies a variety of factors that might influence the parasitic fauna of Scarus fish species in the Red Sea coast of Saudi Arabia.
Further studies are warranted to identify additional factors in our region and explain the interesting finding of sex effect demonstrated in our work.
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