Argulus yawewitus n. sp. is described from pirarucu, Arapaima gigas (Shinz, 1822) from a fish farm in Northeast Brazil. The characteristics that distinguish it from other species are shape of the carapace, abdomen, respiratory areas, the ornamentation and morphology of the antena and antennule, the sexual dimorphism that distinguishes female from male, and the flag-like protrusions on the male’s second and third pair of legs.

Specimens of Dekeiseria amazonica Rapp Py-Daniel, 1985 and Hypostomus oculeus (Fowler, 1943) captured from July 2015 to December 2016, in the Catalão Lake complex, Iranduba, Amazonas, were studied. The specimens of D. amazonica measured 12 – 16.5 (13.70 ± 1.33) and weight (g) 29 – 59 (40.85 ± 9.78) and H. oculeus 12 – 21 (15.80 ± 2.13) and weight (g) 75 - 125.40 (101.11 ± 14.28). Both species were parasitized by the acanthocephalan Gorytocephalus elongorchis Thatcher, 1979 (Neoechinorhynchidae), parasitizing the intestine, with a prevalence of 55% and abundance of 18.  The intensity ranged from 1 to 3 parasites and the average intensity was 1.63 parasites per fish for D. amazonica, and prevalence 59.25%, abundance 29. The intensity of 1 to 4, mean intensity 1.81 for H. oculeus. Two new hosts for G. elongorchis are recorded and their specificity for fish of the Loricariidae is...

Fish are the vertebrates that have the greatest number and diversity of parasitic species. Auchenipterus nuchalis (Spix & Agassiz, 1829) is a small fish that occurs in South America, popularly known as “Peruvian mandi”. It has twilight habits and its diet is basically composed of aquatic insects and microcrustaceans, which are intermediate hosts of several parasitic species. Although fish are the vertebrate group with the highest number of parasitic species, most of these species are still unknown, therefore, the main objective of this study was to know and identify the Nematoda species that parasitize A. nuchalis and calculate the parasitological indices of each species. 38 A. nuchalis were captured in four expeditions in September, October, November and December 2016, in the Catalão lake complex in the municipality of Iranduba, Amazonas, on the left bank of the Solimões river...

Auchenipterus nuchalis (Spix & Agassiz 1829) or Peruvian mandi is a small catfish that occurs in South America, has crepuscular habits and feeds basically on aquatic insects and microcrustaceans. Thirty-eight A. nuchalis were captured in four expeditions during the ebb and dry periods of 2016, in the Catalão lake complex, in the municipality of Iranduba, in the interior of the state of Amazonas, Brazil. Fish averaged 11.8 - 18 (15.1 ± 1.35) cm in standard length and weighed 30.1 - 71.0 (47 ± 10.66) g. The individuals' digestive tract was conserved in 70% ethanol until the analyzes were carried out. Of the total number of fish collected and examined, 21 were parasitized. Temporary and permanent slides were mounted for the identification of parasitic specimens. The measurements of the individuals were made with the aid of a micrometric eyepiece, coupled to an optical microscope. We ...