Blood cells and hematological response of Oxydoras niger (Pisces, Doradidae) collected from the basin of the middle Solimões River, Amazonas State (Brazil), naturally parasitized

Abstract

Oxydoras niger Valenciennes, 1821 (Doradidae) is an endemic fish from the South America river basins (Amazonas, São Francisco, Essequibo and Orinoco Rivers) and used as food by some Amazon people. The aim of this work was to study the effects of parasitism by protozoans and metazoans in the hemogram and the leukocytes features of O. niger collected in the Solimões River basin, Amazonas State, Brazil. Fish (70.3%) were parasitized by Ichthyophthirius multifiliis (Protozoa), Chilodonella sp. (Protozoa), Cosmetocleithrum spp. (Monogenoidea), Paracavisona impudica (Acanthocephala), Cucullanus grandistomis (Nematoda), Digenea and Cestoda, but the highest abundance was of monogenoideans species. This association of parasites caused a significant (p<0.05) increase in hemoglobin concentration and mean corpuscular hemoglobin concentration (MCHC). In blood smears of parasitized and no parasitized fish were found lymphocytes, monocytes, neutrophils, PAS-positive granular leukocytes (PAS-GL) and eosinophils, but only neutrophils had its increase influenced by parasitism, while lymphocytes had a significant (p<0.05) decrease. This was the first study on blood parameters of O. niger in Amazon and the results may be used for comparison in others studies about this fish species.