Analisys of the parasitism by Contracaecum sp. and Eustrongylides sp. in cacharas, Pseudoplatystoma fasciatum (Linnaeus, 1766) (Pisces: Pimelodidae) from Cuiabá river, Mato Grosso, Brazil.

One hundred and forty-nine cacharas (Pseudoplatystoma fasciatum) specimens were captured from Cuiaba river, Mato Grosso State, between october of 2004 to april of 2006, intending to analyse the parasitism by nematode larvae. The prevalence was 100% to parasitism by Contracaecum sp. and/or Eustrongylides sp. larvae. The analysis of the parasitism were done by prevalence record and the localization of the larvae founded. Five cacharas (3,35 %) presented parasitism by Contracaecum larvae in the skeletal muscle and one hundred and forty-seven (98,65 %) on the mesenterium. Fifty cacharas (33,55%) presented Eustrongylides sp. larvae in the skeletal muscle and one hundred seventeen (78,52%) on the mesenterium. The mean intensity of infection was 15,42 larvae/fish for Contracaecum sp. and 6,37 larvae/fish for Eustrongylides sp. The average of weight to the examined fishes was 5,59 kg (1,9-10,5 kg) and the average of the total length was 82,39 cm (63,5-105 cm). Correlation between biomethric parameters as host s total length and weight and the intensity of infection was not observed.