First record of metazoan parasites of hybrids between the genera Colossoma and Piaractus in natural environments.

The practice of hybridization is carried out globally in fish farms. Here, we present the first record of the parasitic fauna of hybrids among genus Colossoma and Piaractus in natural environments. We identified a total of 48 hybrids, nine F1 hybrids (nuclear DNA from both species present in the cross) and 38 advanced hybrids (nuclear DNA from one species), both from crosses between Piaractus brachypomus and Piaractus mesopotamicus, and one F1 "tambacu" corresponding to cross between Colossoma macropomum and Piaractus mesopotamicus. This is the first record of Anacanthorus penilabiatus, Anacanthorus toledoensis, Mymarothecium viatorum, Mymarothecium ianwhittington, Haementeria sp., Dadaytrema oxycephala, Rondonia rondoni, and Echinorhynchus gomesi parasitizing hybrids collected in a natural environment. With this, we expand knowledge about the diversity of fish and parasites in the upper Paraná River and warn about the risk that fish escapes can cause in the basin.

Components influencing parasitism by Dadaytrema oxycephala (Digenea: Cladorchiidae) in Neotropical fish.

The components that mold the structure of parasitic fauna are used as objects of study in an attempt to find patterns in their distribution. It is known that phylogeny (represented by specificity), host ecological traits (for example, feeding habits, position of the water column, reproductive strategies, body size, and age), and the environment affect the distribution and occurrence of parasites. In tropical regions, digeneans show high diversity, and the species Dadaytrema oxycephala is known to parasitize a wide range of host species. In this context, the objective of the present study is to analyze the components that affect the occurrence of D. oxycephala in Neotropical fish. We used data from the literature that contained the abundance of this parasite, as well as the geographic location and host species, and evaluated the influence of ecological traits, specificity, and latitude on parasite abundance, using a generalized linear mixed model (GLMM). The abundance of D. oxycephala can be explained by trophic level and position in the water column and latitude. However, coevolutionary processes are also extremely important, and the distribution of this parasite was not equal, showing high abundance for the genus Piaractus, which are the preferred hosts, even if the parasite is considered generalist. In short, host ecological traits are the important components in the distribution and occurrence of D. oxycephala, as well as the latitude.

Feeding of larvae of the hybrid surubim Pseudoplatystoma sp under two conditions of food management / Alimentação de larvas do surubim híbrido Pseudoplatystoma sp sob duas condições de manejo alimentar

We evaluated the growth and diet composition of hybrid surubim larvae (Pseudoplatystoma corruscans x P. reticulatum) produced in two fish farming by using different systems of feeding with natural plankton: M I, larvae are transferred to fertilized fish pond for being freely fed with natural plankton; M II, larvae are remained inside laboratory in glass fiber boxes and plankton are gathered with a plankton net and offered in a controlled way. It was collected 10 individuals daily during the feeding period with live plankton for 20 days. After the biometry, stomachs were opened and the food items identified and quantified by the volumetric method. The items were represented by algae, protozoa, microcrustacean, insect larvae and surubim fragments (cannibalism). The items with higher volumetric percentage were Chironomidae larvae (29.25%) followed by surubim fragments (19.68%) in M I, and surubim fragments (21.85%) and Moina micrura (19.97%) in MII. The items Chydorus sp., Diaphanosoma sp., sp. Macrothrix and Ephemeroptera larvae were found only in fish of M I, while algae Ulothrix sp., Oscillatoria sp. and the protozoa Difflugia sp were only found in stomachs of surubim from M II. Regarding the growth, the surubim had grown faster in M I.

Este trabalho avaliou o crescimento e a composição da dieta de larvas do surubim híbrido (Pseudoplatystoma corruscans x P. reticulatum) produzidas em duas pisciculturas que utilizam sistemas diferentes de alimentação com plâncton natural: M I, as larvas são transferidas para viveiros previamente fertilizados para se alimentarem livremente com plâncton natural e M II, as larvas permanecem no laboratório em caixas de fibra de vidro e o plâncton são coletados com rede e oferecidos de forma controlada. Foram coletados dez exemplares por dia durante 20 dias. Após a biometria e a retirada dos estômagos, os itens alimentares foram identificados e quantificados por meio do método volumétrico. Os itens com maiores percentuais volumétricos foram larvas de Chironomidae (29,25%) seguido de restos de surubim (19,68%) em M I e restos de surubim (21,85%) e Moina micrura (19,97%) em M II. Os itens Chidorus sp., Diaphanosoma sp., Macrotrix SP. e larvas de Ephemeroptera foram encontrados apenas nos estômagos dos surubins do M I, enquanto as algas Ulothrix sp., Oscillatoria sp., assim como o protozoário do gênero Diflugia , foram observados apenas nos estômagos dos surubins do M II. Em relação ao crescimento, os surubins do M I apresentaram crescimento mais rápido do que em M II.