Light and Scanning Electron Microscopy (SEM) of Ortholinea africanus Abdel-Ghaffar et al., 2008 (Myxozoa: Myxosporea) Infecting Tilapia Fish Oreochromis niloticus (Osteichthyes: Cichlidae) with Description of Preparation of Coelozoic Myxosporea for SEM

Ortholinea africanus Abdel-Ghaffar et al., 2008 is re-described using light and scanning electron microscopy (SEM) to reveal the external ornamentation of the spores. Present spores matched the original description in morphology but were larger in all dimensions. They measured 9.6 ± 0.8 (8.1–10.9) μm in length, 9.5 ± 0.6 (8.8–10.9) μm in width and 8.9 ± 0.4 (8.6–9.1) μm in thickness. Polar capsules were 3.9 ± 0.3 (3.0–4.3) μm in length with polar filaments turned 4–6 turns. The pattern of polar filament coils was different in each of the polar capsules. In the same spore, one capsule contained oblique filament turns to the longitudinal axis of the capsule, while the other capsule contained perpendicular turns. SEM revealed completely different shell ridge patterns than those described by light microscopy in the original description. This emphasizes the necessity of SEM in the reliable description of any myxosporean genera with external shell ornamentation like Ortholinea and Chloromyxum. The present species is considered the first (purely) freshwater Ortholinea described from a proper freshwater host. Three different methods of isolation and preparation of coelozoic spores for SEM were evaluated. The best combination was using a syringe filter holder with a membrane filter of 5 μm pore nucleopore filters.