No abstract

A total of 30 specimens of the Amazonian electric knifefish, Brachyhypopomus beebei Schultz, 1944 (Gymnotiformes: Hypopomidae), were collected from the Peixe-Boi River in the state of Pará, Brazil (1°06’59” S; 47°18’26” W). Fragments of the brain tissue were extracted for analysis via optical microscopy, and 18 specimens (60%) presented microparasites of the genus Myxobolus, with unequal capsules. The spores were 18.6 µm (17.7-19.8 µm) long and 8.6 µm (8.4-9.0 µm) wide; the largest polar capsule was 13.0 µm (12.4-13.4 µm) long and 5.6 µm (5.3-6.0 µm) wide, and the smallest capsule was 5.0 µm (4.5-5.3 µm) long and 2.5 µm (2.3-2.6 µm) wide. Infected brain fragments were extracted for histological processing and staining with hematoxylin-eosin and Ziehl-Neelsen. Some fragments were conserved in ethanol for molecular genetics analysis. A partial sequence of the 18S DNA gene was obtained from the spores, which did not correspond to any other sequences deposited in GenBank, although it did form a clade with other Myxobolus parasites of the nervous system. The morphological data, together with molecular phylogeny, supported the designation of a new species Myxobolus freitasi n. sp.

A new species of Myxobolus parasitizing the arterial bulb and cardiac musculature of the freshwater fish Pimelodus ornatus Kner, 1858, from the Arari river in the municipality of Cachoeira do Arari, island of Marajó, Pará, Brazil, was described. In the present study, the observed prevalence of myxozoan parasites in the heart tissue of the hosts was 20% (6/30). The myxozoans observed had mature biconvex spores, slightly rounded, an anterior end with two pyriform polar capsules and a posterior end with very evident sporoplasm, measuring 8 ± 0.2 μmin length. The spore width was 5.8 ± 0.4 μm, with a thickness of 3.4 ± 0.2μm. The length of the polar capsules was 3.6 ± 0.3 μm and the width was 1.2 ± 0.2μm, with 6 to 7 turns of the polar filament. The divergences observed, regarding the morphometric and genetic structure of SSU rDNA, in relation to other Myxobolidae already described in the literature, confirm the description of the new species Myxobolus rangeli n. sp.