Thelohanellus nikolskii infections

Borz, eka, ak, Borkhanuddin, Muhammad Hafiz, Cech, abor, Kalm, Moln, an, ar, Hallett, Sascha L., Sz, Csaba & ekely, 2021, New data on Thelohanellus nikolskii Achmerov, 1955 (Myxosporea, Myxobolidae) a parasite of the common carp (Cyprinus carpio, L.): The actinospore stage, intrapiscine tissue preference and molecular sequence, International Journal for Parasitology: Parasites and Wildlife 15, pp. 112-119 : 114

3.1. General observations of Thelohanellus nikolskii infections in Hungary

Thelohanellus nikolskii infection was observed in carp fry cultured in ponds from the second half of July to September (Summer) ( Fig. 1 ). The first external sign of infection was darkening of the fin and appearance of dark colour nodules in the fin-rays of 3–4 cm long carp. In some fish the fins were eroded (see Moln´ar and Kov´acs-Gayer, 1981–1982; Moln´ar, 1982). Mature plasmodia filled with myxospores appeared at the end of July and early August ( Fig. 2 ). By the end of August most myxospores were released from opened plasmodia and in the autumn months only distortions of the fins marked past infections. Less frequently, late formation of cysts were recorded also in September in 8–16 cm long fingerlings. The ultrastructure of the spores corresponded to T. nikolskii spores described by Desser et al. (1983). In two year-old carp mostly scale infections were observed but less frequently fin infections also occurred. In the three year-old carp Thelohanellus plasmodia were found only in the scales. These plasmodia infected series of scales causing roughness on the surface of fish ( Fig. 3 ). Concurrent infections on the scales and fins were not recorded. The earliest scale-thelohanellosis was observed at the beginning of May (spring) and the latest one was recorded in the middle of June. In these infections, plasmodia were located at the outer periphery of the scales, in the non-overlapping region. The plasmodium was surrounded by a very thin cartilaginous layer. The original compact cartilaginous plate of the scale was damaged and only calcified islands could be recognised ( Fig. 4A ). The ultrastructure of the plasmodia and the myxospores obtained from the scales ( Fig. 4 AB) corresponded to those described by Moshu and Moln´ar (1997). The myxospores obtained from fin and scale cysts had a similar shape and overlapped in measurements ( Table 2).

Figures

Fig. 1. Thelohanellus nikolskii cysts on the fins of carp fingerlings.

Fig. 2. A: Section of an infected fin, containing T. nikolskii cysts, stained with hematoxilin-eosin. Cartilage of finray (cf) is next to the cyst. Plasmodium (p) is in the achromatic tegument, mature myxospores (s) are in the middle, sporoblasts (sb) are at the edges. Around the plasmodium, there is a thick connective tissue (ct) layer, containing cartilaginous elements (c). Multilayer epithelium (e) is the outer layer. B: T. nikolskii myxospores from the plasmodium.

Fig. 3. Thelohanellus cysts on the scales of an aged common carp specimen.

Fig. 4. A: Cross section of infected scales, stained with hematoxilin-eosin. The plasmodia (p) are filled with myxospores (s) and are surrounded by cartilaginous tissue (c) of the scales, covered by the epithelium layer (e). B: T. nikolskii myxospores from a plasmodium in the scale.