Insemination of the monogenean Neobenedenia girellae (Capsalidae, Benedeniinae)

In vitro spermatophore formation and insemination of Neobenedenia girellae (Monogenea: Capsalidae, Benedeniinae) were recorded on video and described for the first time. Upon contact of two individuals, the anterior adhesive discs of the donor firmly attached to the dorsal tegument of the recipient and the donor's fore body strongly contracted such that the genital pore region protruded and the penis was pushed anteriorly to protrude through the genital pore. It is hypothesised that the donor penis mechanically damaged the tegument of the recipient. The sperm and spermatophore matrix were released together through the penis, which was placed under the left anterior attachment disc immediately behind the adhesive pad. The spermatophore matrix containing the spermatozoa became solid and attached to the dorsal surface of recipient's body. When observed under scanning electron microscopy, the spermatophores were irregularly shaped, with a diameter of 52-83μm. Under light microscopy they consisted of a proximal eosinophilic matrix portion and a distal thin-walled portion containing spermatozoa. Both parts were enclosed with a thin outer casing. Insemination occurred during and after spermatophore formation. Three types of insemination were recorded, unilateral and mutual insemination and self-insemination. The presence of self-insemination indicates that even a single N. girellae on a cultured fish may cause a significant parasite infection in the entire aquaculture system.