This study evaluated the ectoparasite distribution on the gill archs of pond-reared pacu (Piaractus mesopotamicusHolmberg, 1887), hybrid patinga (P. mesopotamicusfemale x P. brachypomus(Cuvier, 1817) male), hybrid tambacu (Colossoma macropomum(Cuvier, 1816) female x P. mesopotamicus male) and hybrid surubim (Pseudoplatystoma reticulatumfemale x P. corruscansSpix & Agassiz, 1829 male). Atotal of 300 fish were examined from fish farms in West-Central Brazil for parasitological assessment of the gill arches I, II, III and IV, from the outer to inner arch, respectively. Only the monogenean Mymarothecium boegeriCohen & Kohn, 2005 and Anacanthorus penilabiatusBoeger, Husak & Martins, 1995 from the hybrid patinga showed the greatest (p<0.05) mean intensities on the gill arch I when compared to gill arch IV. Microhabitat preference was not observed in the other fish examined. Cope...

Few studies have been done to evaluate the monogenean microhabitat preference. This study evaluated the monogenean distribution among different gill arches of Nile tilapia Oreochromis niloticus and seasonality. A total of 89 fish were captured in a pond located in Chapecó, Santa Catarina, for parasitological analysis. After fish euthanasia, the gill arches were removed, separated from the most external to the most internal and named as I, II, III and IV. Transparency, pH, oxygen, temperature, alkalinity, conductivity, ammonia, iron, orthophosphate, sulfide, nitrite and nitrate of water pond were measured. In spring 2008 the mean abundances of the monogeneans (Scutogyrus longicornis, Cychlidogyrus sclerosus, C. thurstonae and C. tilapiae) in the arches I, II, III and IV were, respectively, 11.45, 14.45, 13.8, 13.15, in summer 2008 theywere 13.12, 12.25, 14.94, 21.53, in summer 2009 they ...