ПАРАЗИТОЦЕНОЗ СУДАКА (Sander lucioperca) КУРШСКОГО ЗАЛИВА

Паразитофауна судака водоемов Калининградской области изучалась фрагментарно, и данные о ней носят устаревший характер. Для оценки ихтиопатологического состояния рыбы необходим постоянный мониторинг изменений в составе паразитофауны и показателей зараженности. Проведены четырехлетние исследования паразитофауны судака, обитающего в российской части Куршского залива (Балтийское море). У судака обнаружено 18 видов паразитических орга-низмов: миксоспоридии Myxobolus dispar; микроспоридии Glugea luciopercae; моногенеи Ancyrocephalus paradoxus; цестоды Triaenophorus nodulosus, Diphyllo-bothrium latum; трематоды Bunocotyle cingulate, Diplostomum spathaceum, Tylodel-phys clavata, Bunodera luciopercae, Azygia lucii, Ichthyocotylurus platycephalus, I. variegatus, Bucephalus polymorphus; нематоды Raphidascaris acus, Camallanus lacustris; скребни Acanthocephalus lucii, Corynosoma strumosum; паразитические ракообразные Achtheres percarum. Полный паразитологический анализ проводился по методике, разработанной И. Е. Быховской-Павловской. В паразитоценозе судака преобладают паразиты со сложным жизненным циклом (со сменой промежуточных хозяев). Так, в 2016 г. их доля составила 76,5 % (13 видов); 2017 – 73,4 (11); 2018 –71,4 (10); 2019 – 73,4% (11 видов), тогда как с прямым циклом развития в 2016 г. было 23,5%; 2017 – 26,6; 2018 – 28,6; 2019 – 26,6% (по четыре вида в каждом исследуемом году) паразитов. Повышение зараженности судака трематодами может указывать на процессы эвтрофикации в водоеме. За четыре года исследований наблюдались значительные различия в составе паразитофауны и экстенсивности заражения отдельных видов паразитических организмов. Ос-новной путь заражения паразитами со сложным циклом развития – трофический. Представители класса трематод доминируют в паразитофауне судака Куршского залива (восемь видов). Наибольшая экстенсивность инвазии зарегистрирована у моногенеи Ancyrocephalus paradoxus (100% в 2019 г.), метацеркария трематоды Ichthyocotylurus platycephalus (100% в 2019 г.) и паразитического ракообразного Achtheres percarum (100% в 2016-2019 гг.).

A systematic review of the parasites (Plathelminthes: Trematoda) of the Wels catfish (Silurus glanis L., 1758)

The Wels catfish or sheatfish (Silurus glanis L., 1758) is one of the important commercial fishes. Its native range extends from Eastern Europe to Western Asia. Recently, the species range has expanded both to the west and south due to the introduction. In the water bodies of Azerbaijan, the Wels catfish exists at the southernmost border of its range. It was recorded from the Kura River and its basin. There is no survey of parasitological studies on the trematodes of the Wels catfish. The previous papers have not covered all systematic groups or all the areas where the fish is distributed. Based on the literature data, we prepared a systematic review of the Wels catfish trematodes within the catfish present-day range (native area plus the areas of introduction), including Azerbaijan. The list is given according to the system of parasitic organisms implemented in the Catalog of parasites of freshwater fishes of North Asia. We also took into account new studies in the trematode taxonomy. Each species is provided with the following data: synonyms, habitat in the fish body, collecting localities, geographic distribution within the catfish range, infection rates, and references. As a result, 33 trematode species were found in the Wels catfish. They belong to three orders (Aspidogastridea ‒ 1 species, Strigeida ‒ 16 species, and Plagiorchiida ‒ 16 species), 15 families and 24 genera. Of these, 14 species are distributed in the waterbodies of Azerbaijan. The family Diplostomidae (9 species) dominates among the Wels catfish’ trematode parasites. The most Wels catfish trematodes within its whole range are Bucephalus polymorphus, Orientocreadium siluri and Diplostomum spathaceum. We established that Aspidogaster limacoides, Plagioporus skrjabini, Phyllodistomum petruschewskii were recorded from Ukraine only, Allocreadium siluri and Bolboforus confusus, from Uzbekistan, and Asymphylodora kubanica, Bychowskycreadium bychowsky, Bychowskycreadium schiliani, Diplostomum mergi, Diplostomum chromatophorum, and Diplostomum paraspathaceum from Azerbaijan.

The distribution of digenean metacercariae within bream (Abramis brama) gill apparatus: preferences, co-occurrence and interactions of parasites

Species-specific microenvironmental preferences and interactions between parasite species have been the focus of many ecological studies. Here, we studied the distribution of ectoparasite species within the gill apparatus of bream (Abramis brama) from Lake Lubāns (Latvia) to establish whether digenean metacercariae: (1) prefer specific patches within the gill apparatus; (2) co-occur in the same patches with monogeneans and copepods within a host individual; and (3) interact with monogeneans and copepods. We recorded all parasites on gill arches of the same host species and used null models to analyse co-occurrences of digenean metacercariae, monogeneans and copepods. Zero-inflated mixture models were used to define the preferred patches of parasites. We found that digenean metacercariae (Bucephalus polymorphus) prefer specific patches of the gill apparatus to encyst, and shared these preferences with monogeneans and copepods, but did not interact with them. We concluded that digenean metacercariae have a species-specific microenvironmental preference to encyst in the gill apparatus and their occurrence (even in high numbers) does not reduce the success of attachment of monogeneans and copepods in the same gill patches.

Presence of Bucephalus polymorphus, Echinoparyphium recurvatum and Aspidogaster limacoides (Platodes, Trematoda) in the visceral mass of Dreissena polymorpha (Mollusca, Bivalvia)

The invasive bivalve species Dreissena polymorpha (Pallas, 1771) has become one of the most dominant spe-cies in many lakes and rivers of Europe and North Ame-rica. The aim of this study was to investigate changes in the structure of the visceral mass depending on the repro-ductive cycle and to determine the presence and effects of trematodes on the zebra mussel. Mussels were collected from the Dubrava dam reservoir during eight sampling sessions from January to December 2000. For histological analysis, 80 mussels were placed in Bouin’s fixative for 24 hours, embedded in paraffin and cut with a microtome into 10 μm slices. The sections were then stained with haema-toxylin and eosin. Analysis of non-infected bivalves indi-cated that gametogenesis started in late summer, while spawning began in April. In July, the majority of mussels were in the post-spawning stage. Two mussels were in-fected with Bucephalus polymorphus, one with Echi-noparyphium recurvatum and one with Aspidogaster lima-coides. Obtained results demonstrated that the gonads were the most affected organs in mussels infected by B. poly-morphus, the infection by A. limacoides resulted in a sig-nificant reduction of all investigated organs, while the infection by E. recurvatum had no visible pathogenic changes in the structure of visceral mass.

The effects of the trematode Bucephalus polymorphus on the reproductive cycle of the zebra mussel Dreissena polymorpha in the Drava River

The effects of the trematode Bucephalus polymorphus on the reproductive cycle of the zebra mussel Dreissena polymorpha were examined in mussel populations from the Drava River. The reproductive cycle was studied by histological examination of the gonads and quantified by an image analysing system to determine changes in volume of the entire visceral mass, gonads, digestive glands and in particular the volume of trematodes. Results confirmed that (1) gonads of D. polymorpha were affected by B. polymorphus infection more than any other organ and (2) development of cercariae in sporocysts of B. polymorphus coincides with host gonad maturation. This is the first study in which the image analysing system was used to determine the effect of trematodes on the reproductive cycle of D. polymorpha. Also, this is the first record of sporocysts of B. polymorphus in D. polymorpha in this part of Europe.