One hundred and twenty‐nine isolates of Trichosporon jirovecii were isolated from the melanized exoskeleton as well as eyestalks, gills, muscle and haemolymph of red swamp crayfish (Procambarus clarkii) collected from the River Nile, during summer 2015. Isolates were similar morphologically, biochemically and genetically. Also, random amplified polymorphic DNA (RAPD) analysis exhibited no polymorphism among the tested isolates. Virulence factors such as chitinase, protease, lipase activities and biofilm formation were examined. Challenge test, using a representative isolate (Tj_ASU8), proved its pathogenicity against crayfish. Magnesium oxide nanoparticles had a good antifungal activity with a minimum fungicidal concentration of 8 mg/ml. To the best of our knowledge, this is the first report for isolation of T. jirovecii from red swamp crayfish, showing melanization, from the River Nile. We assume that infected crayfish may act as a vector for this fungus and can disseminate infection to all susceptible hosts in the vicinity.

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In Egypt, the Nile River is a major supply of Nile perch Lates niloticus Linnaeus, 1758(Asnake, 2018. This fish is one of the most popular and important species in the fishery (Latif, 1974;Rashid, 1995). It is well suited to farming, having large amounts of bone-free white flesh which is rich in protein and vitamins, especially omega-3, which is essential to human nutrition. However, this species is particularly susceptible to parasitic infestation (Asnake, 2018). Parasitism has a major detrimental impact on fish production, industrial productivity and economic values (Basusta et al., 2017).Contracaecum Raillet and Henry, 1912, is a genus of anisakid nematodes with a global distribution (Ángeles-Hernández et al., 2020), comprising over 140 species (Bezerra et al., 2021). This genus is the most abundant and diversified among the Anisakidae (Shamsi, 2019). During the larval development, those nematodes can infect a wide range of aquatic hosts (Di Azevedo et al., 2017). The adults and fourth-stage larvae (L4) can infect marine mammals such as seals and some piscivorous birds such as cormorants, pelicans, darters and herons, which are too be considered definitive hosts

Background Prevalence, morphology, and molecular characteristics of isopodiosis in the European seabass, Dicentrarchus labrax, in Egypt were assessed using light and electron microscopy and polymerase chain reaction targeting the mitochondrial COI (cytochrome oxidase c) gene. Results Adult parasites were found mainly in the branchial cavity between gill arches and to a lesser extent in the buccal cavity. They were morphologically identified as the Cymothoidae Livoneca redmanii Leach, 1818 (Crustacea: Isopoda). Obviously, a 23% prevalence rate of isopods was reported in D. labrax from Egyptian Mediterranean waters. Destructive and degenerative necrotic alterations with complete sloughing of gill lamellae of the infested fish were observed. DNA sequencing of the mitochondrial COI gene confirmed the identification of the parasite which was deposited in the GenBank under accession numbers MW600099, MZ208984, and MZ208985. Furthermore, the phylogenetic analysis demonstrated that parasites emerged from a monophyletic clade closely affiliated with L. redmanii and were clearly distinguished from other isopod genospecies. Conclusion The present investigation addresses L. redmanii infestation in D. labrax in Egypt and affirmed morphological properties via the scanning electron microscopy (SEM) and molecular characteristics of this isopod species. The drastic effects of this parasite on the infected fish were proven both clinically and histopathologically.