This paper presents the morphological, histological and ultrastructural characteristics of
Myxobolus oliveirai
sp. nov., a parasite of the gill filaments in
Brycon hilarii
from the Brazilian Pantanal. Out of 216 B.
hilarii specimens examined (126 wild and 90 cultivated), 38.1% of wild specimens (n = 48) were infected. The parasites form elongated plasmodia primarily in the tip of gill filaments, reaching about 3 mm in length. A thorough comparison with all the
Myxobolus species described from South American hosts, as well as nearly all the
Myxobolus species described so far is provided. Partial sequencing of the 18S rDNA gene revealed a total of 1,527 bp. The
Myxobolus species parasite of
B. hilarii did not match any of the Myxozoa available in GenBank. In the phylogenetic analysis,
M. oliveirai sp. nov. composed a monophyletic group with eight other species: five species of
Myxobolus parasites of mugilid fishes, two parasites of pangasiid and one of centrarchid. Infection prevalence values of the parasite revealed no significant differences between wet and dry seasons or between males and females. The importance of the infection to the farming of the host species is emphasized.
