Expanding morphological knowledge of two nematode species parasitizing Southeastern Brazilian marine fishes

Abstract

Histological approaches have increasingly been incorporated into integrative taxonomy as complementary sources of morphological information. However, their application to parasitic nematodes remains limited. The present study provides a histological characterization of two nematode taxa recovered from marine fishes collected along the coast of the State of Rio de Janeiro, southeastern Brazil: larval specimens of Anisakis sp. from Pogonias cromis (Linnaeus, 1766) and adult specimens of Dichelyne (Cucullanellus) sciaenidicola Timi, Lanfranchi, Tavares & Luque, 2009 from Micropogonias furnieri (Desmarest, 1823). Recovered nematodes were fixed in neutral buffered formalin, processed using routine histological techniques, sectioned at 5 μm, and stained with hematoxylin and eosin and Gomori’s trichrome. Histological examination of Anisakis sp. revealed a thick multilayered cuticle, well-developed somatic musculature, ventriculus, intestine, and boring tooth, corroborating the diagnostic morphology of anisakid larvae. In D. (C.) sciaenidicola, the esophagus exhibited a characteristic division into an anterior isthmus-like region and a posterior bulbous portion, while the intestine displayed small villus-like mucosal projections and a cuticular lining in the anterior digestive tract. The observations obtained were consistent with previous morphological descriptions and provided additional information on the internal organization of both species. The results demonstrate that histological analyses can contribute useful complementary characters for nematode taxonomy, while expanding knowledge of the morphofunctional organization of marine fish parasites from the Brazilian coast.