Parasitic otitis is an inflammatory process that can affect the external to internal cattle ear, causing discomfort in animals, impairing performance, and even leading to animal death. The infection was initially associated with nematodes of the Rhabditis genus in tropical and subtropical regions. Currently, the nematode species described as associated with bovine otitis are Metarhabditis costai, Metarhabditis freitasi, and, more recently, M. blumi. It is worth highlighting that there is still a lack of robust information regarding the morphological details, ultrastructural aspects, and molecular biology data of these species. The Metarhabditis genus is composed of seven species and two more have recently been added. The objective of this study is to update the morphological data using advanced microscopy techniques to emphasize and clarify the main morphological differences between three species of Metarhabditis currently associated with parasitic otitis. Samples of inflammatory exudate were collected from four adult female Gir cattle (Bos taurus indicus) on a farm in Itabira, Minas Gerais state, Brazil. Specimens were analyzed using light microscopy and scanning electron microscopy. Two species, M. costai and M. freitasi, were morphologically identified, consistent with previous reports. Scanning electron microscopy revealed new structural characteristics of the nematode species involved in parasitic otitis compared with M. blumi obtained from the CGC Center. Significant differences were observed in the male posterior region, bursa, and tail. Molecular analysis was conducted to differentiate these three species, and it was observed that the species first associated with otitis formed distinct clusters compared to M. blumi. However, it is important to note that further studies are needed to genetically characterize species of the Metarhabditis genus.

Pterygoplichthys pardalis is an endemic as well as economically important fish species in the Amazon basin. Thirty P. pardalis specimens were purchased at assorted fairs in the city of Manaus. Fish were necropsied, and then, had their organs investigated for parasites. The identified parasites were observed under Light bright field microscopy and that of Scanning Electron Microscopy (SEM). Through the analyses it was observed 219 metazoan parasite specimens, belonging to four taxonomic groups: Monogenoidea, Digenea, Acanthocephala, and Copepoda. Six metazoan parasitic species were identified: Monogenoidea Unilatus unilatus Mizelle and Kritsky, 1967 and Copepoda Therodamas elongatus (Thatcher, 1986) from the gills, Digenea Austrodiplostomum compactum (Lutz, 1928), Megacoelium spinicavum Szidat, 1954 and Diplostomum sp. from the eyes, stomach, and gonads, respectively, and Acanthocephala Gorytocephalus elongorchis Thatcher, 1979 from the intestine. Gorytocephalus elongorchis was the one presenting the highest prevalence value, followed by digeneans M. spinicavum, Diplostomum sp., and A. compactum. The present study has come to provide the very first SEM M. spinicavum, G. elongorchis, and T. elongatus images, thus improving on the up to now available data addressing P. pardalis parasitic fauna, which has been found to be infecting, the fish species presently being marketed in Manaus. Moreover, the current survey has demonstrated the identified parasite species pose no public health concern at all.

Excysted cystacanths of Corynosoma paraevae Amin et al., 2025 (Polymorphidae) were described as a cryptic species from the body cavity of Notothenia coriiceps Richardson, 1844 collected off Galindez Island, Argentine Islands. This description included its molecular analysis, SEM images, and Energy Dispersive X-ray Analysis (EDXA) for the first time which demonstrated highest levels of calcium in all hooks and hook roots compared to sulphur and phosphorus. We report here for the first time a new aspect of elemental analysis of hooks demonstrating the differential distribution of sulphur , phosphorous, calcium, and magnesium at the center and margins of anterior, middle and posterior hooks, and hook roots. In this study, Calcium was found to be the most prevalent element in roots (root edge and root middle) and the center of middle hooks. Phosphorous was also common but not as prevalent as calcium and was highest in the center of the roots and also the middle of all hooks. Interestingly, phosphorous was consistent in all hook roots but was lowest in the center of posterior hooks and roots. Sulphur was negligible or absent in root center of anterior and middle hooks, pronounced in posterior hook root and most prevalent in the edges of all hook tips as well as the edge of the middle hook. The biological importance of this pattern is discussed in terms relevance to hook strength and flexibility, species identity and comparative systematics. This EDXA profile of C. paraevae was distinctly differentiated from that of the morphologically closely related species Corynosoma pseudohamanni Zdzitowiecki, 1984.