Occurrence and effect of trematode metacercariae in two endangered killifishes from Greece

Prevalence and identification of cyathocotylid trematodes infecting African catfish in Egypt

The trematode family Cyathocotylidae infects various hosts worldwide, including birds, mammals, reptiles, and fish. However, the lack of molecular data from adult worms hinders phylogenetic, epidemiological, and host association studies. This study aims to identify the common cyathocotylid trematodes infecting African catfish in Egypt using morphological and molecular evidence. Out of 142 Clarias gariepinus, 123 fish (86.6%) harbored cyathocotylid metacercariae, with a mean metacercarial intensity of 201 ± 38.5/g. Cyathocotylid metacercariae prevalence gradually rose as host size increased. Although there was no significant difference between groups, larger fish had a higher mean metacercarial intensity. The prevalence and intensity were unrelated to the fish gender. Histopathological examination of metacercariae-infected catfish revealed varying degrees of degenerative changes, including intermuscular edema leading to muscle fiber dispersion and atrophy, involving 11% to over 81% of muscle sections. We identified three cyathocotylid metacercariae and eight cyathocotylid adult species from experimental infection using morphometric and molecular data, including internal transcribed spacer (ITS) and/or mitochondrial cytochrome c oxidase subunit 1 (cox1) sequences. We determined the phylogenetic position of these cyathocotylid samples. The ITS sequence analysis linked the isolated Cyathocotylidae sp. 1 and 2 metacercariae to Prohemistomum vivax adults. Mesostephanus appendiculatoides and Paracoenogonimus ovatus were reported for the first time in Egypt. These findings may provide valuable genetic data for future molecular epidemiological and phylogenetic studies of cyathocotylid trematodes.

Distribution ofPomphorhynchus laevis s.l.(Acanthocephala) among fish species at a local scale: importance of fish biomass density

Parasite distribution among hosts is a fundamental aspect of host–parasite interactions. Aggregated parasite distributions within and across host species are commonly reported and potentially influenced by many factors, whether host or parasite specific, or related to host–parasite encounter and compatibility. Yet, the respective role of each in observed parasite distributions are often unclear. Here, we documented the distribution of the acanthocephalan parasitePomphorhynchus laevis sensu lato(s.l.) in two replicate fish host populations. Aggregated distributions were observed in both populations, within and across fish host species. We found a positive abundance–prevalence relationship across fish species, suggesting that resource availability (fish host biomass density) was the main driver ofP. laevis s.l.distribution. This was supported by further positive associations between mean parasite load and fish biomass density. We found little evidence for intensity-dependent regulation within host (i.e. intra-host competition among co-infecting parasites). Furthermore,P. laevis s.l.infection had no detectable effect on fish condition indices, except on the body condition of female barbel (Barbus barbus). Therefore,P. laevis s.l.tended to accumulate with size/age within fish species, and with fish biomass density among fish species, with apparently negligible limitations due to intra-host intensity-dependent regulation of parasite, or to parasite-induced morbidity in fish. The relative availability of final hosts for trophic transmission thus appears to be the main driver ofP. laevis s.l.distribution among fish.

First report of Posthodiplostomum minimum metacercariae and resulting histopathological changes in Bagrus bajad from Lake Nasser, Egypt

Parasitological studies of 100 Bagrus bajad fish were collected from Lake Nasser, Aswan, Egypt. Out of them 75 were infected with metacercariae in two forms; encysted in most visceral organs and free only in air bladder. These were identified morphologically as Posthodiplostomum minimum metacercariae (Strigeidida: Diplostomidae). The intensity of white grub in B. bajad was high in the intestine (30 encysted metacercariae/g). The highest prevalence season observed in summer and the lowest in winter. The histopathological examination revealed encysted metacercariae of different sizes within the intestinal musculature accompanied with granular infiltration with eosinophilia. Degenerative changes were observed in liver and kidney cells, as well as congestion of hepatic sinusoids. Spleen showed both lymphoid and melanomacrophages cells depletion.