RESUMEN
ABSTRACT Brycon hilarii, popularly called piraputanga in Brazil, is a species distributed throughout the whole basin of the river Paraguay. In recent years, the species has been on a repopulation program due to its remarkable decline as a wild species in the region. Assessment of the genetic diversity of broodstock and fingerling stocks in repopulation programs is basic to avoid genetic impacts on wild populations. The genetic variability of the wild population and of the broodstock and fingerling stocks of B. hilarii in a repopulation program in the river Itiquira MT Brazil will be determined. Seven microsatellite loci produced 52 polymorphic alleles and heterozygosity revealed rates between 0.5794 and 0.7204. FIS did not register any endogamy in the broodstock but it was present in fingerlings and wild populations. Intra- and inter-specific genetic variability rates were higher within each combination but not between groups. Grouping in fingerling groups had a lower density when compared to the others. There is a higher genetic proximity between the natural population and broodstock (0.0237) when the distance between populations was analyzed, even though the two were greatly distant from the fingerling group (0.2622 - 0.2617). Results show that the wild population and the broodstock had high genetic variability and low genetic divergence; contrastingly, fingerlings showed mild genetic variability and great divergence when compared to other groups, indicating that they were not adequately constituted.
RESUMEN
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. hilariispecimens examined (126 wild and 90 cultivated), 38.1 percent 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.