First record of Palombitrema triangulum ( Suriano , 1981 ) Suriano , 1997 ( Monogenea : Dactylogyridae ) from freshwater fishes in Brazil

This study reports for the first time the monogenean Palombitrema triangulum Suriano (1981) in freshwater fishes from Brazil, highlighting new sites of infection for this helminth and some morphological differences. Monogeneans were collected on the body surface, gills and nasal cavity of two native fish species from Brazil, Cyphocharax modestus (Fernández-Yépez, 1948) and Cyphocharax nagelii (Steindachner, 1881). A brief morphological characterization of this species is presented.

Cyphocharax modestus (Fernández-Yépez, 1948) and Cyphocharax nagelii (Steindachner, 1881) are both benthopelagic and potamodromous species, zooplanktivorous (juveniles 40-50 days old) and detritivorous (larger individuals) distributed in South America: the first is found in upper Paraná River basin and Paraguay River above Sete Quedas Falls, and the other in upper Paraná River basin in Brazil (Froese and Pauly, 2011).The Peixe's River (48°06'38"W; 22° 49'53.1"S) is a tributary on the left bank of the middle Tiete River basin in Barra Bonita area, São Paulo State, Brazil, its headwaters are in the municipality of Torre de Pedra in the Basaltic Cuesta Botucatu Environmental Preservation Area and is a drainage basin corresponding to 584 km 2 running North to South (Caramaschi, 1986).
Cyphocharax modestus and C. nagelii are common species in Peixe's river, and studies on the occurrence of monogeneans in fishes from this river have not been performed yet.The aim of this study was to report for the first time the occurrence of Palombitrema triangulum Suriano in freshwater fishes from Brazil, highlighting new sites of infection for this helminth.

Material and Methods
During a helminthological survey carried out between March and August 2010, 58 specimens of C. modestus and 56 specimens of C. nagelii were collected from the Peixe's River to study their monogeneans.Fish were collected using nylon monofilament gill nets with mesh sizes of 3-14 cm in three sites of Peixe's River.Nets were placed at 5 pm and removed the next day at 7 am, thus exposed for 14 h.The fish were removed from the nets and each specimen was separated in plastic bags.Some fish were maintained in coolers for one hour until necropsy, and others were frozen and analyzed posteriorly.The gills were removed and the gill arches were separated, placed in vials and filled with hot water (60 to 70° C).The vials were vigorously shaken to detach the parasites from the gill tissues.After 1 hour, absolute alcohol was added to the vials to fix the monogeneans.The body surface and nasal cavity were washed and sieved.
Some specimens were stained with Gomori's trichrome and mounted in Canada balsam, and others were mounted in Gray and Wess' medium (Humason, 1979) to study the sclerotized structures.Differential interference contrast microscopy (Leica DMLB 5000) was used for morphological examination.Measurements were obtained using a computerized image analysis system (LAS, Leica Microsystems, Wetzlar, Germany).Measurements (in micrometers) were expressed as mean followed by the range in parentheses.The illustrations were made with the aid of a camera lucida mounted on a Leica DMLS microscope.Voucher specimens were deposited in the Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, AM, Brazil and Coleção Helmintológica do Instituto de Biociências de Botucatu (CHIBB), Botucatu, SP, Brazil.

Morphological description (Figures 1 and 2)
Based on twenty specimens: Dactylogyridae, Ancyrocetahlinae.Body fusiforme.Tegument smooth.Cephalic lobes incipient or absent, cephalic glands at level of pharynx.Eyes absent and accessory granules in cephalic

Discussion
Morphometrical and morphological features of the studied specimens (Table 1) matches the description of P. triangulum by Suriano (1981).However, our specimens showed a ventral and dorsal anchor with superficial root more developed than the specimens described by the former authors and with filament present; in our specimens the dorsal bar can present two formats and the ventral bar present a prominent projection that is absent in specimens described by Suriano (1981).This may be related to intraspecies variations that are common in Monogenea or to an adaptive process (Kritsky et al., 1995).These same authors studied the morphometric variability of specimens of Scleroductus Jara and Cone, 1989 reported from the external surface of four Siluriformes from the Guandu River and questioned whether the observed variations in morphology and size are of specific value or result from influences of host and/or environmental factors.
Although there are evidences of monogeneans with a broad host species spectrum, most of them show high host specificity, occurring on a single species or on closely related fishes.The monogeneans of the family Dactylogyridae are usually found in the gills, but they can inhabit the nasal cavities and, in rare cases, other body parts of hosts (Zanolo and Yamamura, 2006).The species found in this study were described only in the gills of their host (Suriano, 1981), however we recorded it in other sites with high infestation prevalence, intensity and abundance (Table 2).This data represent important information about the biology of this parasite, increasing the knowledge of the monogenean host-parasite interaction.This is the first record of P. triangulum in freshwater fishes from Brazil, and also the first report for the hosts C. modestus and C. nagelii.