Description of two new species of Myxobolus Bütschli, 1892, M. peleci n. sp. and M. cultrati n. sp., detected during an intensive mortality of the sichel, Pelecus cultratus (L.) (Cyprinidae), in Lake Balaton, Hungary.

In the summer of 2014, mass mortality of the sichel, Pelecus cultratus (L.), was observed in Lake Balaton, Hungary. Parasitological examination conducted in the framework of a complete diagnostic survey revealed myxozoan infections. Two species of Myxobolus Bütschli, 1892 were found, one in the gill lamellae and another in the eyes. Following this mass mortality, 113 sichel specimens were examined during a 14-month period. Gill infection with scattered spores in the lamellae was found in 51 fish, while infection in the eyes was recorded in three specimens only. Based upon the morphological and molecular biological data the species from the gills is described here as Myxobolus peleci n. sp. and the species from the eye as M. cultrati n. sp. The 18S rDNA sequences of the two species proved that they differ from all known Myxobolus spp. with sequence data available in the GenBank database. Histological examinations revealed that the spores found in the gill lamellae were derived from plasmodia developing in and around the afferent branchial arteries of the gill arches. No mortality of sichel was recorded in 2015. Infection with these two Myxobolus spp. does not seem to play a role in the mortality of the host fish.

The occurrence of metacercariae of Petasiger (Digenea: Echinostomatidae) in an unusual site, within the lateral line scales of cyprinid fishes.

During a regular veterinary inspection of fishes from Lake Balaton, Hungary, echinostomatid metacercariae (Digenea), with collar spines characteristic of species of the genera Petasiger Dietz, 1909 and Paryphostomum Dietz, 1909, were found in the lateral line scales of a roach Rutilus rutilus (Linnaeus), an apparently unique site. In a subsequent examination of 586 fishes from 20 different species, similar infections were found in 11 species. The infection was virtually restricted to the lateral line scales, other scales being infected only incidentally. These encysted metacercariae had 27 collar spines, including eight larger angle spines and 19 smaller dorsal spines arranged in two rows. Two types of metacercarial cyst were found. One type had a cyst diameter of 138-171 µm × 105-120 µm and three central dorsal spines that were larger than the remainder and tended to resemble the angle spines. The second type of metacercarial cyst had a diameter of 128-157 µm × 105-115 µm and all 19 dorsal spines of the metacercaria were of a similar size. ITS sequences of the second type of metacercaria exhibited a 100% similarity to sequences of two adult Petasiger phalacrocoracis (Yamaguti, 1939) specimens collected from the gut of Phalacrocorax carbo (Linnaeus) in Hungary and to P. phalacrocoracis deposited in the GenBank database. Sequences obtained from two metacercariae of the first type showed a 2.8-2.9 % difference from sequences of the second type of metacercaria and from those of adult specimens of P. phalacrocoracis from cormorants. Based on these results, the second type metacercaria is considered to be a larval stage of P. phalacrocoracis, but the identity of the first type is uncertain. The unusual location of these metacercariae in the lateral line scales is discussed in relation to their transmission.