Digenea of Hoplias intermedius and Odhner, 1902, and Pseudosellacotyla lutzi (Freitas, 1941) Yamaguti, 1953. The prevalence of the metacercariae was higher than that of the adult digeneans of erythrinids from the upper São Francisco River as a result of piscivorous feeding habits of these adult erythrinids. The presence of metacercariae and adult digeneans indicate that they act as intermediate and definitive hosts, respectively, in their biological cycles. Hoplias intermedius is a new host for the four species of Digenea, and the São Francisco River basin is a new location for the known geographical distributions of P. spatula and P. lutzi.

The cystidicolid nematode Cystidicoloides fischeri (Travassos, Artigas and Pereira, 1928) is redescribed from specimens collected from the stomach of the San Francisco piranha, Pygocentrus piraya (Cuvier), and the white piranha, Serrasalmus brandtii (Lütken) (both Characidae, Characiformes) (new host records), from the Três Marias Reservoir, Upper São Francisco River, Minas Gerais state, Brazil. The morphology of this type species of Cystidicoloides Skinker, 1931, studied with both light and scanning electron microscopy, is characterized by some taxonomically important, previously unreported features, such as the presence of a cephalic cuticular collarette, subdorsal and subventral cephalic spikes, cuticular tooth-like elevations inside the prostom, deirids, area rugosa, and details in the structure of the cephalic end. Heliconema izecksohni Fabio, 1982 is transferred to Cystidicoloides as C. izecksohni (Fabio, 1982) n. comb. Cystidicoloides uniseriata Valovaya and Valter, 1988 is considered a species inquirenda with uncertain generic appurtenance. The presence of subdorsal and subventral cephalic spikes and the collarette are characteristic of Cystidicoloides, comprising only species parasitizing Neotropical fishes. The species from salmonids in the Holarctic, hitherto reported mostly as Cystidicoloides ephemeridarum (Linstow, 1872), belongs to a different, newly erected genus, for which the name Salmonema n. gen. (type species S. ephemeridarum) is now proposed. Cystidicoloides prevosti (Choquette, 1951) is transferred to Salmonema as S. prevosti (Choquette, 1951) n. comb. Sterliadochona ssavini Skryabin, 1948 and Sterliadochona Skryabin, 1948 are considered as species inquirenda and a genus inquirendum, respectively. A key to species of Cystidicoloides is provided.

ABSTRACT. Ecological and reproductive aspects of Neoechinorhynchus pimelodiBrasi l-Sato & Pavanelli , 1998, in Pimelodus macula/us Lacepede, 1803 collected in the Sao Francisco river during periods of drought (July 1995 and1996) and flood ings (January 1996 and 1997) of this river basin are provided. In tropical regions where the amount of rainfall alters the hydrological regimen of limnol ogical systems water temperature has not had an imp0l1ant role in infectio ns ofN. pimelodi in P. macula/lis. Prevalence was somewhat higher during drought periods. Intensity of infection varied sl ightly between collecting periods. Mature male and female acanthocephalans were present in all periods. Females were predominant. Mature females were present in higher numbers during flooding periods with a corresponding decrease in juvenile acanthocephalans. Recruitment and constant losses of N. pilllelodi seem to be controlled by transm ission mechani sms independently of dens ity. Mec han isms may consist of infected prey availability (potential intermediate hosts) and changes of preferred alimentalY items in the diets of juvenile and mature P. maclllallls. KEY WORDS. Acanthocephala, Neoechinorhynchuspimelodi, Pimelodus macula/us, ecology, reproduction There are no published works in Brazil which refer to the populational dynamics of fish parasites. This is especially true of acanthocephalans. Research work on populational dynamics of neoechinorhynchid acanthocephalans in fresh water fi sh of temperate countri es have shown seasonal aspects in the life cycles of these parasites. This is chiefly due to oscillations in water temperature. In the present paper aspects of ecology and reproduction of acanthocephal ans in fresh water fish are analysed within a tropical geographical di stribution. The lotic system o[the Sao Francisco river basin is basically altered by rainfall variations which characterise flooding and drought periods. MATERIAL AND METHODSPimelodus macula/us Lacepede, 1803, "mand i-amarelo", were collected in the Sao Francisco river, state of Minas Gerais, Brazil, downstream the Tres Marias reservoir. In this lotic environment co ll ections were carried out in July 1995 and

One hundred and thirteen specimens of Franciscodoras marmoratus (Reinhardt, 1874) were collected in the upper São Francisco River (18° 12' 32" S, 45° 15' 41" W, state of Minas Gerais) between September, 1999 and January, 2004 to investigate their parasite fauna. From this total, 45 (39.8%) were afflicted by at least one parasite species. The parasitic richness consisted of six species represented by Hirudinea (n = 20), Monogenoidea (n = 25), Eucestoda (n = 55), Nematoda (n = 1, n = 2) and Acanthocephala (n = 41) found in the dry and wet periods making a total of 144 specimens. Proteocephalus renaudi Chambrier & Vaucher, 1994 was the only species with prevalence higher than 10% and a typical aggregate distribution pattern. The prevalence, intensity and abundance of P. renaudi were not influenced by the total length or sex of the hosts or by the collection periods. The relative condition factor indicated that the health of the P. renaudi hosts was not significantly affected in relation to fish not infected by parasites. The fish stocked in tanks before necropsy were opportunistically infested by Lernaea cyprinacea Yashuv, 1959. The various parasites found indicate that F. marmoratus is omnivorous and a potential definitive host. The parasite species, except for Acanthocephala, have expanded their known geographic distribution to the São Francisco River Basin. The parasite community was considered isolationist because of the low endoparasite diversity, infrapopulations with low intensity, lack of evidence of parasite interactions and sparse signs of parasite aggression against their hosts.Keywords: Franciscodoras marmoratus, parasitic community, relative condition factor, freshwater fish parasites, São Francisco River. RESUMO