Occurrence of two novel actinospore types (Cnidaria: Myxozoa) in fish farms in Mato Grosso do Sul state, Brazil

Synopsis of the aurantiactinomyxon collective group (Cnidaria, Myxozoa), with a discussion on the validity of morphotype definition and demise of guyenotia

Aurantiactinomyxon is one of the most diverse myxozoan collective groups, comprising types that mostly infect freshwater and marine oligochaetes belonging to the family Naididae Ehrenberg, 1828, but also Lumbriculidae Claus, 1872. In this study, a comprehensive revision of all known aurantiactinomyxon types is performed and highlights the fallibility of using the form and length of the valvular processes as main criterion for differentiating among style-less actinospore morphotypes. The demise of the guyenotia collective group is proposed based on the ambiguous features of several types that allow conformity with both the aurantiactinomyxon and guyenotia definitions. Nonetheless, the information presently available clearly shows that a general shift is needed in our approach to actinospore grouping, which should probably be based on actinospore functionality relative to environment and host ecology, rather than on morphology. Life cycle studies based on experimental transmission and molecular inferences of the 18S rDNA have linked aurantiactinomyxon (including former guyenotia) to myxozoans belonging to a diverse array of genera, including Chloromyxum, Henneguya, Hoferellus, Myxobolus, Paramyxidium, Thelohanellus and Zschokkella. This undoubtedly shows a high capacity of the aurantiactinomyxon morphotype to promote infection in intrinsically distinct vertebrate hosts and environmental habitats, consequently increasing interest in its study for attaining a better understanding of myxozoan-host interactions. The identification of novel and known types, however, is impeded by the lack of concise information allowing a comprehensive analysis of biological, morphological, and molecular criteria. In this sense, the compilation of data presented in this study will ultimately help researchers seeking to perform reliable identifications.

Henneguya polarislonga n. sp. (Cnidaria: Myxosporea) parasitizing Astyanax lacustris (Lütken, 1875) with an insight on its life cycle

Henneguya polarislonga n. sp. is described from the gills of Astyanax lacustris (Lütken, 1875) (Characiformes, Characidae) from streams of the Middle Paranapanema River, Upper Paraná River basin, in the São Paulo State, Brazil. The proposed new species is supported by a combination of morphological and molecular characterization (partial fragment of the SSU rDNA). Thirty specimens of A. lacustris were analyzed and myxospores were found in the gill lamellae of one specimen (Prevalence = 3.3%). Henneguya polarislonga n. sp. was morphometrically and genetically distinct from other Henneguya spp. previously described in Astyanax spp., mainly differing in the total length and caudal appendages length of the mature myxospores. Comparative analysis of the SSU rDNA sequences revealed that Seisactinomyxon-type actinospores previously reported parasitizing oligochaetes are developmental stages of the life cycle of Henneguya polarislonga n. sp. (similarity of 99.9%). This is the first time that an actinospore and a myxospore are correlated through molecular analysis in Brazil, contributing to the knowledge of the myxozoan ecology and biodiversity.

Pathological and immunological analyses of Thelohanellus kitauei (Myxozoa:Myxosporea) infection in the scattered mirror carp, Cyprinus carpio

Thelohanellus kitauei is a spore-forming myxosporean parasite prevalent in scattered mirror carp (Cyprinus carpio) that generates numerous cysts in the intestine and causes mass mortality in fish. To investigate the infection and mortality induced by T. kitauei in pond-reared farms in Luo-Jiang (104°51’N, 31°31’E), southwest China, morphological and molecular analyses of infected fish were conducted. Natural and specific immune indicators were further evaluated to determine the immunological effects of response to parasitic infection. The infectious parasite was identified as Thelohanellus kitauei based on morphological, 18S rDNA and infectious characteristics. Scattered mirror carp was determined as the specific intermediate host of the parasite. However, T. kitauei still caused considerable damage to the fish, in particular, injury and blockage of the intestines, resulting in malnutrition and even death. The mature spores of T. kitauei colonize the intestinal submucosa of carp and form cysts of various sizes that block the intestinal tract and release spores into the enteric cavity upon rupture, leading to the next phase of T. kitauei growth. Moreover, T. kitauei-infected carp showed weaker innate immunity. IgM is involved in the fight against parasitic infection while cytokines, such as IL-6, IL-1β and TNF-α, had an impact on infection processes. To our knowledge, this is the first report to show that T. kitauei infects and causes death in scattered mirror carp. Our collective findings from systematic pathology, morphology and immunology experiments provide a foundation for further research on infections by this type of parasite and development of effective treatment strategies.