The purpose of the present research is to evaluate the degree of the statistical association between the total burden of parasites in the South American Catfish, Rhamdia sapo, and hematological variables studied under natural conditions. The following 12 parasite species were identified: 2 ciliate protozoans, 1 flagellate, 1 monogenean, 3 digeneans, 1 cestode, 2 nematodes, and 2 crustaceans. Of the parasite species collected from the tegument, branchias, body cavity, and digestive tube, some of them (namely, Argulus violaceus, Urocleidoides mastigatus, Hysterothylacium rhamdiae, Acanthostomun gnerii, Proteocephalus jamdiae, Trichodina sp. and Cucullanus sp.) have been previously cited. However, Ichthyophthirius multifiliis, Spironucleus sp., Lernaea cyprinacea, and Thometrema sp. are cited for the first time in Argentina as a parasite of this fish. The non-parametrical Spearman’s rank correlation test indicated that the total burden of parasites in the South American Catfish, Rhamdia sapo, exerts no significant action under the hematological variables studied in this research, namely, red blood cell count, white blood cell count, thrombocyte count, hemoglobin concentration, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration.