Conventional Identification of Pathogenic Fungi Isolated from Fresh Water Aquarium Fish (O. niloticus and C. gariepinus) Combined with Molecular Identification of Saprolegnia parasitica in Egypt

This study aimed to investigate fungi exist in the skin/fins, gills, and internal organs of two economically essential diseased fresh water fish species with amplification of Internal Transcribed Spacer (ITS1-ITS4) regions of ribosomal DNA as the reference method for Saprolegnia parasitica identification, in Egypt. Among 500 samples from Oreochromis niloticus and Clarias gariepinus, mycological investigations had revealed 148 (29.6%) fungal isolates with 6 genera: Aspergillus spp. (51.3%) with A. niger as the most dominant species, Saprolegnia spp (16.2%), Penicillum spp., Alternaria spp. (10.8% each), Cladosporium spp. and C. albicans (5.4%). Moreover, skin/fins (55.4%) was the most affected area followed by gills (18.9%) and internal organs (liver 10.8%, kidney 10.2%, eyes 2.7% and spleen 2%). The highest fungal infection rate was demonstrated during autumn (41.7%), followed by winter season (36%). The intraperitoneal-challenged C. gariepinus groups with A. flavus, C. albicans, A. niger and Cladosporium spp. displayed the highest cumulative mortality rate (100, 80, 70 and 70% respectively), while the intramuscular challenged C. gariepinus groups with A. flavus, A. niger and C. albicans revealed the highest mortality rate (60, 50 and 50% respectively). Furthermore, presumptive identification of the 24 isolates was initially suggestive of Saprolegnia species. Therefore, PCR assay joined with partial sequencing of ITS gene was confirmed the identification of 9 representative S. parasitica strains. This finding confirmed that the diseased fresh water fish species may harbor potential clinically applicable fungal species.