engleski

Early detection of Thelohanellus nikolskii infection by Alcian blue-Alizarin Red S double staining technique

Thelohanellus nikolskii Akhmerov, 1955 is a non-native myxosporean parasite that was originally described in eastern Russia and Vietnam (ZHANG et al., 2013). The life cycle of T. nikolskii has two phases. The aurantiactinospore phase takes place in an annelid host (Tubifex tubifex) while the myxospore phase occurs in the common carp (Cyprinus carpio) (SZÉKELY et al., 1998). In common carp, the parasite forms large polysporic plasmodia in the fins and scales. This study describes a case of thelohanellosis caused by T. nikolskii in semi-intensively cultured 47-day old common carp fry. The common carp fry was sampled on a fish farm in Croatia, during the regular monitoring of health status. A total of 140 fry were sampled from 5 to 47 days post hatching (DPH). The collected fry were killed by an overdose of tricaine methane sulfonate (MS 222) and complete parasitological examination was conducted. The DINGERKUS and UHLER (1977) method was used for the demonstration of the ossification process and development of Thelohanellus infection. Stained samples were analyzed by Olympus SZX7 stereoscopic microscope, using a digital camera (Olympus DP12) and Cell B software (Soft Imaging System). T. nikolskii infection was found only in one specimen at the age of 47 DPH. By 47 DPH, the whole skeleton of common carp was almost completely ossified. The infection was characterised by the presence of numerous plasmodia on the whole surface of the fins. In this Alcian Blue-Alizarin Red S stained fry, plasmodia were not difficult to detect and were located on the finrays, on the surface of the hemisegments. At the site of infection, T. nikolskii produced weakly blue stained ‘cartilaginous capsule’. Within this capsule, small cartilaginous and/or bony islets were observed. Today this pathogenic Thelohanellus species is widely distributed among Croatian fish farms.

Fish ; Thelohanellus nikolskii ; Alcian Blue-Alizarin Red S

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