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

Abstract

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.

Molecular biological studies of adult and metacercarial stages of Petasiger exaeretus Dietz, 1909 (Digenea: Echinostomatidae)

“…The collection of parasites, as well as the morphological and histological methods used basically corresponded to those described by Molnár et al (2015). In that study, only specimens of Petasiger phalacrocoracis were recorded from the gut of cormorants.…”

“…Similarly, the postponed sequencing of a Type 2 echinostomatid metacercaria (PA3) collected from a cyprinid fish, the roach [Rutilus rutilus (Linnaeus)], was carried out for both genes. Additionally, the 28S rDNA was partially sequenced for the Petasiger and Paryphostomum samples published by Molnár et al (2015). Adult worms were identified according to the keys of Kostadinova (2005), Kostadinova et al (2002) and Faltýnková et al (2008).…”

“…In a recent paper, Molnár et al (2015) reported finding echinostomatid metacercariae in the lateral line organ of some Hungarian fish species. These metacercariae, characterised by 27 collar spines, could be related to Paryphostomum Dietz, 1909 andPetasiger Dietz, 1909 species infecting the intestine of fish-eating birds, especially cormorants.…”

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Molnár et al (2015) reported two types of echinostomatid metacercariae in the lateral line organ of Hungarian fish species. Type 1 metacercariae possessed 27 collar spines and 16 uniform and three larger dorsal spines, whereas Type 2 metacercariae bore 27 collar spines and 19 equal-sized dorsal spines.

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Molecular and morphological characterization of Isthmiophora melis (Schrank, 1788) Luhe, 1909 (Digenea: Echinostomatidae) from American mink (Neovison vison) and European polecat (Mustela putorius) in Lithuania

“…A phylogenetic analysis and comparison of the I. melis sequence (AY168932) (collected from molluscs) with other sequences shows its close similarity to sequences of P. radiatum (KM972998, KM973000, AY245708, and KM972999). A close similarity between the I. melis sequence (AY168932) and P. radiatum sequences has already been identifi ed by Molnár et al, (2015). The intermediate hosts of P. radiatum are molluscs of the genus Planorbis (Našincová et al, 1993).…”