(Myxozoa) in the blood of Metynnis lippincottianus (Osteichthyes: Serrasalmidae) from eastern Amazon, Brazil

Myxozoans are obligatory parasites and can be found in various organs and bloodstreams of fish, thus, the objective of this work was to describe the occurrence of Myxobolus spp. in the circulating blood of Metynnis lippincottianus from River Curiaú, Macapá City, eastern Amazon, Brazil. The samples of M. lippincottianus (11) were caught using cast net and gillnets. The fish blood was collected by puncturing the caudal vessel, using needles and syringes containing 10% of EDTA solution. Blood smear were prepared and panchromatic stained with a combination of May Grunwald-Giemsa-Wright, for observation and examination of the parasitic structures in optical microscope. Tissues from the kidney was examined using specific stereoscopic binoculars to check for the presence of cysts, lesions and parasites. The prevalence of Myxobolus spp. infecting the circulating blood of the fish was 36.36% (4/11) and 15 spores of mixosporyds were visualized. Myxobolus spp. had a prevalence of 54.55% (6/11) in host's kidney tissue and the morphometric spores data converge with observed in the blood. The morphological characteristics of the spores in the blood samples revealed two morphotypes of Myxobolus spp. This is the sixth occurrence recorded of Myxobolus spp. infecting fish blood in Brazil.

Two new species of Anacanthorus (Monogenoidea, Dactylogyridae) parasitizing serrasalmid fish in Brazil

During studies on fish parasites, two new species of Anacanthorus were found parasitizing serrasalmid fishes, Anacanthorus simpliciphallus sp. n. from the hybrid Piaractus mesopotamicus x Piaractus brachypomus and Anacanthorus brandtii sp. n. from Serrasalmus brandtii. Anacanthorus simpliciphallus sp. n. resembles Anacanthorus reginae in the morphology of the male copulatory organ (MCO) and accessory piece but differs from A. reginae in terms of the smaller size of the accessory piece, which corresponds approximately half the size of the MCO and by the presence of a conspicuous metraterm, with a membranous terminal region. Anacanthorus brandtii sp. n. differs from Anacanthorus scapanus by the expansion of the accessory piece, from Anacanthorus jegui by the ratio MCO (male copulatory organ) /AP (accessory piece) and by the expansion of hook shank, from Anacanthorus sciponophallus and A. reginae by the ratio MCO/AP. Anacanthorus brandtii sp. n. can be distinguished from A. reginae and A. simpliciphallus sp.n. by the size of hooks which is similar in A. reginae and A. simpliciphallus sp. n. and dissimilar in A. brandtii sp. n. The two new species also differ from each other by the expansion of shank.

Dynamics of Growth in Purebred Pacu (Piaractus mesopotamicus) and Tambaqui (Colossoma macropomum), and Their Reciprocal Hybrids, under Varied Feeding Programs: Insights from Nonlinear Models

We evaluated the growth performance of pacu and tambaqui and their reciprocal hybrids (tambacu and paqui) under different feeding programs. We raised 30 individuals from each species and their respective crosses, distributing them into three replicate cages with 10 individuals each. Throughout the 5-month experimental period, the fish were weighed six times while exposed to diverse feeding regimens involving three commercial diets with varying combinations of crude protein (CP) levels: 24%, 28%, and 32%. Growth curves were adjusted using nonlinear models. The evaluation period was insufficient for adjusting the logistic model for the tambaqui and paqui treatments with the highest initial protein intake. Pure pacu had a higher (p < 0.05) growth rate (k = 0.0185) than in the tambacu hybrid (k = 0.0134) and proved to have an early performance since animals from this group reached their weight at inflection faster. Despite growing more slowly, tambacu reached a higher (p < 0.05) final weight (A = 1137.12) than in the pacu (A = 889.12). Among the feeding programs, animals that received less CP showed greater growth potential; however, longer evaluation is important to verify if the initial CP intake has no significant positive effect on fish growth.

The phylogenetic position of Anacanthorus (Monogenea, Dactylogyridae) parasitizing Brazilian serrasalmids (Characiformes)

Anacanthorus (Anacanthorinae) is one of the most speciose and common genera of neotropical monogeneans, yet there are still many gaps in our knowledge concerning their diversity and phylogeny. We performed phylogenetic analyses of molecular sequences in order to investigate the phylogenetic position within the Dactylogyridae of Anacanthorus spp. infesting serrasalmids from two Brazilian river basins. Sequences of partial 28S rDNA obtained for nine species of Anacanthorus and Mymarothecium viatorum parasitizing serrasalmids and the published sequences of other members of the Dactylogyridae were included in the phylogenetic reconstruction. Phylogenetic analyses supported the monophyly of anacanthorine monogeneans. The Anacanthorinae (represented in this study by Anacanthorus spp.) formed a monophyletic group included in a large clade together with a group of solely freshwater Ancyrocephalinae and species of the Ancylodiscoidinae. Mymarothecium viatorum (Ancyrocephalinae) was placed within the clade of freshwater Ancyrocephalinae. The phylogenetic analyses indicated that the relationships among species of Anacanthorus reflect those of their serrasalmid hosts: the first subgroup includes a species specific to hosts assigned to Piaractus, a member of the "pacus" lineage; the second subgroup includes a species parasitizing the "Myleus-like pacus" lineage; and the third subgroup includes species parasitizing the lineage of the "true piranhas". We suggest that Anacanthorus and their serrasalmid hosts can be considered a useful model to assess host-parasite biogeography and coevolution in the neotropics. However, future studies focusing on a wider spectrum of host species and their specific Anacanthorus spp. are needed in order to investigate coevolution in this highly diversified system.