Using scanning electron microscopy (SEM) to study morphology and morphometry of the isolated haptoral sclerites of three distinct diplozoid species

Diplozoidae infects the gills of cyprinid fishes in Africa, Europe, and Asia. Traditionally the hardened internal structures, crucial for identification of diplozoid species, are studied using light microscopy. Recently, the sclerotised haptoral structures of an African diplozoid, Paradiplozoon vaalense, were successfully isolated and visualised using scanning electron microscopy (SEM). In this paper, the haptoral sclerites of three diplozoid species are compared using SEM for the first time. Paradiplozoon ichthyoxanthon and Paradiplozoon vaalense occur on Labeobarbus and Labeo species, respectively, in the Vaal River system, South Africa, while Diplozoon paradoxum is widely-distributed in Europe and Asia, infecting several host species. Diplozoon paradoxum is a well-studied species, as well as being the type species of the family and ideal for inclusion in an exploratory study for comparative purposes. SEM study of D. paradoxum and P. ichthyoxanthon provided valuable information regarding surface morphology of the attachment structures hitherto not observed. Elaborate morphometric study of the haptoral hooks were incorporated, adding 12 point-to-point measurements to current morphometric characteristics. The results were analysed statistically, and significant differences support absolute separation (100.00%) of the three species following discriminant analysis. These point-to-point measurements could also be used for light microscopical study in the future and aid species delimitation within the Diplozoidae.