Gobioides broussonnetii ( Gobiidae ) : a new host for Pterobothrium crassicolle ( Trypanorhyncha ) on Marajó Island , northern Brazil Gobioides broussonnetii ( Gobiidae ) : um novo hospedeiro para Pterobothrium crassicolle ( Trypanorhyncha ) na Ilha do Marajó , Brasil

In the present study, the cestoid Pterobothrium crassicolle Diesing, 1850 (Trypanorhyncha), was observed parasitizing specimens of the violet goby (Gobioides broussonnetii Lacepède, 1800) collected from the estuary of the Paracauarí River on Marajó Island in the north of the Brazilian state of Pará, between January 2009 and December 2010. Tissue samples were analyzed, which led to identification of blastocysts containing plerocercoid larvae. These larvae were processed for scanning electron microscopy. Sixty G. broussonnetii specimens were dissected, and P. crassicolle was found in 48 (80%) of them. The violet goby, G. broussonnetii, is a new host for P. crassicolle.


Introduction
The waters of the Amazon estuary are inhabited by both marine and freshwater fish species, which constitute an important economic resource for the region (BARTHEM, 1985).The violet goby or dragon fish, Gobioides broussonnetii Lacepède, 1800, is the largest member of the Gobiidae and forms an important link in the food chain of this estuary.It prefers muddy bays and freshwater estuaries, but is also found at sea on muddy bottoms, widely distributed around the southern USA, Central America, the Caribbean islands and northeastern South America (BRAGANÇA, 2005).
Trypanorhyncha is characterized by the presence of a bothridiumlike scolex, with reversible tentacles, with a larval, plerocercus or plerocercoid, or post-larval stage, which can be found in teleost fish, crustaceans and, occasionally, reptiles.The adults are found in the gastrointestinal tracts of elasmobranch fish (CAMPBELL;BEVERIDGE, 1994).
While these parasites are well known from studies in southern Brazil (PALM, 1997), few data are available on their occurrence in this country's northern (Amazon) region.The present study identifies G. broussonnetii as a host of Pterobothrium crassicolle in the region of Marajó Island, in the estuary of the Amazon River in northern Brazil.

Materials and Methods
Violet goby (G.broussonnetii) specimens (n = 60) were collected monthly between January 2009 and December 2010 in the area of the estuary of the Paracauarí River in the municipality of Salvaterra, which is located on Marajó Island, in the north of the Brazilian state of Pará (0° 58' S and 49° 34' W) (MMA/ SISBIO authorization no.27119-1).The specimens were kept in an oxygenated aquarium filled with water from the capture site, and were subsequently transported in aerated plastic bags to the Edilson Matos Research Laboratory at the Federal University of Pará (FUPA) in the mainland city of Belém.The specimens were anesthetized with MS 222 (Sandoz Laboratories) for measurement of biometric parameters and subsequent dissection.
Tissues from host samples were analyzed using a stereomicroscope, which led to identification of blastocysts containing plerocercus larvae.These larvae were processed following the procedures recommended by Eiras (1994).The taxonomic classification of the trypanorhynch helminths was based on the studies of Rego et al. (1974), Campbell and Beveridge (1994) and Palm (1997).The prevalence of the parasites and the mean intensity of infection were calculated in accordance with Bush et al. (1997).
For scanning electron microscopy (SEM), the larvae were fixed in 5% glutaraldehyde buffered with sodium cacodylate (pH 7.2) for 12 hours at 4 °C, and then washed overnight in the same buffer solution and post-fixed in 2% OsO 4 buffered with the same solution for 3 hours at 4 °C.The samples were then dehydrated in an increasing series of ethanol concentrations.The larvae were dried to the critical point, metalized with a fine (20 nm) layer of gold, and photographed in a LEO 1459 VP SEM operated at 80 kV.The specimens were also photographed in a Hitachi TM 3000 Tabletop electron microscope (Hitachi TM 3000), for which they were prepared following the same procedure, except for the metalization, which was not carried out in this case.Representative specimens of the species found were deposited in the Helminthological Collection of the Oswaldo Cruz Institute (CHIOC no.37845 a-b), Rio de Janeiro, RJ, Brazil.

Results and Discussion
The 60 G. broussonnetii specimens analyzed in the present study had a mean total length of 21.7 ± 4.5 cm, and 48 (80.0%) were found to be parasitized by at least one blastocyst, with mean intensity of 1.04.Fifty blastocysts were collected and processed, and all were identified as P. crassicolle, and no infections by any other helminth species were recorded.All the specimens were found in the mesentery of the fish, and it seemed that these parasites did not show any preference regarding host gender.

Taxonomy:
Superfamily Otobothrioidea Dollfus, 1942 Family Pterobothriidea Pintner, 1931 Pterobothrium crassicolle Diesing, 1850 (Figure 1a-f ) Principal morphological traits of P. crassicolle based on 30 plerocerci collected from G. broussonnetii: Plerocercus with blastocyst.Scolex elongated, acraspedote, subcylindrical and narrower than the pars bothridialis.Pars bothridialis with four piriform bothria on mobile pedicles with rounded edges (Figure 1a).Pars vaginalis is long, corresponding to more than half the length of the scolex.The tentacle sheath is initially relatively smooth, with elongated bulbs.Pars postbulbosa does not overlap the pars bothridialis.Distinctive basal armature and swelling present on bothridial and antibothridial faces of tentacle; macrohooks present on antibothridial face; asymmetrical basal swelling of tentacle present.Hook files 1 (1') widely separated, falciform; intercalary row(s) present proximally to each principal row; intercalary rows extend onto bothridial surface to merge with band of hooks occupying midline of bothridial surface of tentacle.Hooks in row 1 (1') widely spaced, falciform; hook rows interspersed with each principal hook row, the interspersed row extending along the bothridial surface bordered with the group of hooks, occupying the median line of the bothridial surface of the tentacle (Figure 1b-d).
Metabasal and apical shielding formed by the principal rows of large hooks in an alternating half-spiral arrangement, heteromorphic and hollow.Small hooks interspersed between the principal rows on both the bothrial and antibothrial surfaces (Figure 1e, f ).
A number of studies have recorded the presence of plerocerci of P. crassicolle in fish collected off the coast of Brazil.In the north of the Brazilian state of Pará, this species was recorded for the first time by Diesing (1850) (reference unexamined, apud Rego, 1987) in Bagrus marinus, and Rego (1987) provided a redescription of the species in Brachyplatystoma flavicans, B. vaillantii and B. marinus.The prevalence of infection recorded in G. broussonnetii was relatively high in comparison with previous studies in southern Brazil, while the intensity was comparatively low.São Clemente (1986a, b) recorded a prevalence of 11% and mean intensity of 1.52 in whitemouth croakers (Micropogonias furnieri) from Rio de Janeiro, for example, and Porto et al. (2009) recorded values of 26.7% and 2.25, respectively, for this species from the same region (Niterói).At the southern extremity of this country, in Rio Grande, Pereira Jr. and Boeger (2005) recorded a prevalence of 66.7% and a mean intensity of infection of 5.2 in some species of sciaenid fish.The present report is the first record of P. crassicolle infecting the violet goby, G. broussonnetii.