Gyrodactylus attach to fish using a terminal specialized attachment organ, the opisthaptor which is equipped with two sharp, centrally positioned hooks called hamuli and an array of 16 peripherally distributed hooks (Fig.
a) Light microphotography of Gyrodactylus cichlidarum parasitizing the Nile tilapia (scale bar = 50 [micro]m), b) ventral bar (scale bar = 10 [micro]m), c) the opisthaptor consists of two centrally positioned large hooks or hamuli (h) joined by two connecting bars, a simple dorsal bar (d) and an approximately triangular shaped ventral bar (v).
The attachment apparatus of adults consist of four pairs of clamps and a pair of small central hooks situated on the ventral side of the opisthaptor
. Due to the complicated determination of several groups of monogenean parasites, molecular markers based on species-specific variability in the ribosomal DNA region (rDNA) their cytogenetics have been designed and shown to be useful for precise species identification [1-5].