Influence of Physicochemical Features of Aquatic Habitat on Biodiversity Indices of Gill Ectoparasitic Microfauna of Two Sympatric, Cohabitant Cichlid Hosts Refuging in Burullus Lake and Nourishing Streams

Abstract

This study tested the null hypothesis that sympatric and cohabiting cichlid species with similar ecological and phylogenetic traits host comparable helminthic microfauna, and that habitat characteristics significantly influence the structure of their parasitic communities. We conducted a comparative analysis of two parasitic taxa, Monogenea (Cichlidogyrus, Scutogyrus, Gyrodactylus) and Digenea (Centrocestis formosanus) infesting the gills of Oreochromis niloticus and Sarotherodon galillaeus in Burullus Lake and adjacent nourishing streams (Egypt) during 2023. Sampled habitats included Burullus Bay (lake outlet), Shakhlouba ecotourism zone (southern lake region), and Drain-7 (agricultural stream). Among 460 examined fish (248 of O. niloticus and 212 of S. galillaeus), 3,038 gill parasites were identified (1,448 monogeneans, 1,590 digenean cysts). The Shakhlouba zone showed the highest parasite prevalence (40.42%), followed by Drain-7 (31.27%) and Burullus Bay (28.31%). Monogeneans dominated in Shakhlouba, particularly C. halli typicus (66.30%), C. thurstonae (70.41%), and G. cichlidarum (49.07%), whereas digenean cysts were least abundant there (20.50%). In contrast, Burullus Bay hosted the highest digenean cyst count (41.38%). Canonical correspondence analysis (CCA) revealed that digenean cyst prevalence correlated positively with salinity (EC, TDS, Cl⁻) and minerals (Na⁺, K⁺, N) but negatively with water turbidity and temperature. Simpson’s diversity index (D = 0.914, 1-D = 0.086, 1/D = 1.09) indicated low parasite diversity. A variance-to-mean ratio >1 suggested clumped parasite distribution. Results supported the null hypothesis: both cichlid species exhibited species-poor, similar helminthic communities, and parasite assemblages were shaped by habitat features (water volume, turbidity, vegetation, flow regime). The study highlighted how environmental factors driven by human activity and climate change affect parasite transmission in sympatric hosts.