Infections by helminth parasites in "puyenes", Galaxias maculatus (Galaxiidae, Salmoniformes), from Southern Argentina with special reference to Tylodelphys barilochensis (Digenea, Platyhelminthes).

The occurrence of Tylodelphys barilochensis, Acanthostomoides apophalliformis, Contracaecum sp. and Camallanus corderoi infecting Galaxias maculatus ("puyenes") was quantified for the first time in Lake Nahuel Huapi, southern Argentina. T. barilochensis was recorded in this lake for the first time. The role of G. maculatus population in transmission of parasites to the salmonids is more important for Contracaecum sp. (prevalence 14-34%) and A. apophalliformis (prevalence 30-54%) than for C. corderoi (prevalence 6-8%). The absence of Diphyllobothrium spp. in samples shows that the G. maculatus population does not play any role in the life cycles of these important zoonotic parasites. The sex of the host had no effect on T. barilochensis abundance. Statistical differences in T. barilochensis abundance between "puyenes" of the same size class between sampling stations and positive correlation between prevalence of infected snails and T. barilochensis abundance in fish suggest that different stocks have been sampled. Factors influencing T. barilochensis abundance are discussed.     

Multivariate analyses in the taxonomy of two species of Tylodelphys Diesing, 1850 (Trematoda: Diplostomidae) from Galaxias maculatus (Teleostei: Galaxiidae)

Three Tylodelphys species are known to co-exist in the brain of Galaxias maculatus: T argentinus, T. barilochensis and T. crubensis. In order to determine the species present in the G. maculatus from Lake Gutiérrez, specimens were captured using baited traps every month from April to December, 1995. A total of 1,526 metacercariae were separated for identification, and multivariate techniques were applied on meristic variables measured on stained mounted metacercariae. Two species were identified through these techniques: T. barilochensis and T. crubensis.     

In vitro effect of rainbow trout (Oncorhynchus mykiss) serum in Tylodelphys sp. (trematoda, Diplosromatidae) metacercariae]

Here, it has been described that normal fresh sera from rainbow trout (Oncorhynchus mykiss) were able to lyse Tylodelphys sp. metacercariae isolated from Galaxias maculatus (Jenyns, 1842) (Teleostei, Galaxiidae) brain. This effect was time dependent, and progressively increased since 1 h up to 18 h incubation. There were oscillations in the ability of different sera samples to lyse these parasites. Similar values were achieved with other salmonid sera, and also with normal human sera pool. The lytic activity was abolished by heat-inactivated sera, by zymosan treatment and by incubation in the presence of EDTA. However, the mean values obtained in the presence of EGTA-Mg++ did not significantly differ from those found with sera as a source of complement. The results of this study suggested the role of complement alternative pathway on Tylodephys sp. in vitro lysis, under our experimental conditions.     

Trematode metacercariae from the cranial cavity of African catfish Clarias gariepinus (Burchell, 1822) from Lake Tana,Ethiopia

Metacercariae of two species of trematodes from the fam. Diplostomidae from the cranial cavity of the African catfish Clarias gariepinus are described. The metacercaria Tylodelphys grandis n. sp. is described for the first time. Data are presented on the infection rate of catfishes in Lake Tana.     

Philureter trigoniopsis, a new genus and species (Dactylogyridae, Ancyrocephalinae) from the ureters and urinary bladder of Galaxias maculatus (Osmeriformes: Galaxiidae) in Patagonia (Argentina)

The monotypic Philureter n. gen. (Ancyrocephalinae; Dactylogyridae) is proposed to accommodate Philureter trigoniopsis n. sp. with the following features: presence of a cuplike ventral haptor armed with 14 hooks and 2 anchor/bar complexes; dorsal pair of anchors poorly defined and variable in shape, 1 frequently absent; tandem, intercecal gonads, testis bilaterally lobulated. Philureter trigoniopsis n. sp. is described from the ureters and urinary bladder of Galaxias maculatus (Jenyns, 1842) (Osmeriformes) in Patagonian Andean lakes, Argentina.     

A new genus of Cystidicolid nematode from the stomach of Galaxias maculatus (Osmeriformes: Galaxiidae) in Patagonia (Argentina)

During a parasitological survey of Galaxias maculatus (Jenyns) from Patagonian Andean Lakes, specimens of a new species of nematode were collected from the stomach of fish and studied by light and scanning electron microscopy. This species is described as the only member of a newly proposed genus of Cystidicolidae by having oral opening dorsoventrally elongated, 2 lateral pseudolabia, 4 cephalic papillae, stoma (vestibule) elongated, esophagus divided into anterior muscular and posterior glandular sections, and caudal alae in males. Placonema n. gen. (Habronematoidea, Cystidicolidae) is characterized by the combination of the following features: oral opening dorsoventrally elongated demarcated by 4 sclerotized plates and 2 well-developed pseudolabia projected to the buccal cavity, each pseudolabium with conspicuous, conical, anterior protuberances. Four cephalic papillae and deirids simple. Male with caudal alae, area rugosa absent, 4 pairs of preanal papillae, unpaired papilla present on anterior cloacal lip, and 6 pairs of postanal papillae. Larvigerous eggs without filaments. Placonema pataguense n. gen. n. sp. infects the stomach of G. maculatus from Lake Patagua (Patagonia, Argentina) and is the first species of Cystidicolidae described from G. maculatus.     

Infection patterns of Tylodelphys barilochensis and T. crubensis (Trematoda: Diplostomatidae) metacercariae in Galaxias maculatus (Osmeriformes: Galaxiidae) from two Patagonian lakes and observations on their geographical distribution in the southern Andean region,Argentina

In the Patagonian Andean region, 2 species of diplostomatids parasitize the brains of Galaxias maculatus.The purpose of this study was to evaluate seasonal variation, spatial variation, and association with host age in the transmission of Tylodelphys barilochensis and T. crubensis in several oligotrophic lakes in Argentinian Patagonia. Fishes were captured monthly in Lake Gutiérrez and bimonthly in Lake Escondido. One summer or autumn sample was also taken in several other Patagonian lakes. Infection parameters were calculated and compared using nonparametric tests. The 2 species co-occurred in most of the sampled lakes, with high values of prevalence and mean intensity. In Lake Gutiérrez and Lake Escondido, the intensity of both diplostomatid species did not show significant differences between sexes and co-varied with host length. All age classes were infected; maximum prevalence values were reached before maximum mean intensity values in the 1-yr age class. A seasonal pattern of prevalence and mean intensity of the 2 parasite species with autumn mean intensity values differing significantly from those of the other seasons was evident only in Lake Gutiérrez.     

Parasitism in fishes and human riverside communities of the Huillinco and Natri lakes (Great Island of Chiloé), Chile

In April and December 1989, 35 fish from Lake Huillinco (42 degrees 48'S, 74 degrees 02'W) and 36 fish from Lake Natri (42 degrees 48'S, 73 degrees 50'W), in the Great Island of Chiloé (Chile) were examined. Coprological samples from 159 persons, 17 dogs, 19 pigs and 4 cats from around both lakes were examined for Diphyllobothrium spp. infection. In the Lake Huillinco the following helminths of fishes were determined: Contracaecum sp. and Hysterothylacium sp. in Salmo trutta, Cauque mauleanum and Eleginops maclovinus; Dichelyne (Cucullanellus) dichelyneformis in S. trutta and E. maclovinus and Scolex pleuronectis in S. trutta. One specimen of Mugil cephalus did not show helminth parasites. Prevalence of infection were greater for Contracaecum sp. in S. trutta (75.0%) and C. mauleanum (76.0%); and Hysterothylacium sp. in E. maclovinus (75.0%). Mean intensity was higher for D. (C.) dichelyneformis in E. maclovinus. Contracaecum sp. in S. trutta, Oncorhynchus mykiss, Oncorhynchus kisutch and Galaxias maculatus; Acanthocephalus sp. in S. trutta and G. maculatus, S. pleuronectis in O. mykiss and Cystidicoloides sp. in G. maculatus were determined at Lake Natri. Prevalence and intensity of infection were higher for Contracaecum sp. in S. trutta and O. kisutch. Infection by Diphyllobothrium sp. was determined in one domestic cat. Prevalence of infection by intestinal protozoan and helminths in human population only showed significative differences for Ascaris lumbricoides and Trichuris trichiura that were higher in the Lake Huillinco. Importance of natural infection by helminth parasites for fish in cultured condition and possible mechanisms of infections in relation to the diet of fishes are discussed.     

Impact of a caged-trout farm on parasites of Galaxias maculatus in Lake Moreno, southern Argentina

The present study was conducted to determine the impact of a caged-trout farm on the helminth parasites of the wild fish puyen chico (Galaxias maculatus) in Lake Moreno, southern Argentina. Samples of water, fish (G. maculatus), and snails (Heleobia hatcheri) were taken at 4 sampling stations in January 2001. Wild fish were parasitized by 8 helminth species, all of which are endemic in the region; therefore, the farm did not introduce any helminth parasite to G. maculatus. Fish captured near the farm were not infected by the digenean Steganoderma szidati, whereas the abundance of the digenean Acanthostomoides apophalliformis in these fish was significantly lower than that in fish captured away from the farm. This lower abundance may be explained by the absence in this area of the snail H. hatcheri, the parasite's first intermediate host, because of the effect of sediments and ammonium produced by the farm. To our knowledge, this is the first study in the Americas linking fish-farm pollution to helminth parasites in wild fish.     

A new genus of dactylogyrid from the gills of Galaxias maculatus (Osmeriformes: Galaxiidae) in Maullín Basin, Patagonia, Chile

During a parasitological survey of Galaxias maculatus (Jenyns, 1842) in the Maullín Basin (Chilean Patagonia), specimens of a new species of Monogenea were collected from the gills. This species is described as the only member of a proposed new genus, Inserotrema n. gen. (Dactylogyridae, Ancyrocephalinae), characterized by similar hooks with 2 subunits, overlapping gonads, coiled cirrus with counterclockwise rings, articulated accessory piece formed by 2 parts, a needlelike sclerite threading the distal part of the MCO, and a sclerotized midventral vagina. This new genus is proposed for dactylogyrids from gills of galaxiids (Galaxiidae). Inserotrema puyei n. sp. infects gills of G. maculatus from Llanquihue Lake, Maullín River, and Maullín Estuary. This is the first species of Ancyrocephalinae described from gills of a galaxiid.     

Life history studies of heterophyid trematodes in the Neotropical region: Ascocotyle (Leighia) hadra sp. n.

The life cycle of Ascocotyle (Leighia) hadra n. sp. was experimentally reproduced, starting from cercariae from naturally infected Littoridina parchappei, collected from Los Ranchos stream, near Mercedes city, Buenos Aires Province, Argentina. Metacercariae were found encysted in the liver and mesentery of experimentally and naturally infected fishes Cnesterodon decemmaculatus and Jenynsia lineata. Adults were obtained experimentally in chicks and mice. The natural host is unknown. The new species is compared with Ascocotyle (Leighia) mcintoshi Price 1936 as described by Leigh, 1974, differing in behavior and morphology of cercarial, metacercarial and adult stages.     

Population dynamics of Tylodelphys destructor and Diplostomum mordax (Digenea: Diplostomidae) co-occurring in the brain of Patagonian silversides from Lake Pellegrini,Patagonia, Argentina

Studies on infection patterns of diplostomid parasites in commercially exploited fishes have not been done in Patagonia (Argentina). The aim of this work was to study the population dynamics of two diplostomid species in the brain of patagonian silversides (Odontesthes hatchery), the interaction between them, and effect on health and physical condition of the hosts. Tylodelphys destructor and Diplostomum mordax metacercariae in the brain of Patagonian silversides in Lake Pellegrini were studied between January 1991 and February 1992. Tylodelphys destructor parasitized all silversides examined; prevalence of D. mordax varied between 7% and 100%. Mean intensity for T. destructor was 35-140 and for D. mordax was 3-49. Highest mean intensities of T. destructor coincided with the lowest mean intensities of D. mordax. Recruitment seems to occur from July-November for T. destructor and from April-June for D. mordax, revealing a temporal segregation with inverse patterns of infection and recruitment. Tylodelphys destructor has higher intensities in the brain of the older fish, whereas D. mordax did not, suggesting another type of segregation. There were no evidences of gross pathology. No covariation between abundance of larvae and condition factor, gonadosomatic index, and gut fullness was detected.     

Population dynamics of Philureter trigoniopsis (Monogenea: Ancyrocephalinae) from urinary organs of Galaxias maculatus (Osmeriformes: Galaxiidae) in a cold temperate Andean Patagonian lake (Argentina)

Philureter trigoniopsis parasitizes the ureters and urinary bladder of Galaxias maculatus in Patagonian Andean lakes. To investigate factors associated with variation in the prevalence and intensity of this monogenean, fish were sampled periodically over 2 yr in Lake Gutiérrez. Prevalence and mean intensity are higher in smaller fishes than in larger ones. A seasonal pattern was observed, with peak recruitment and peak mean intensity occurring in early spring (September), followed by lows in late summer (January-February). Galaxias maculatus length classes are spatially segregated due to seasonal migrations, so the annual infection cycle is characterized by higher prevalence and intensity from late winter to early summer in the smaller fish from the deep zone of the lake.     

New Dalyelliidae (Platyhelminthes, Rhabditophora) from Buenos Aires Province, Argentina, and their stylet ultrastructure

Two new species of Dalyellidae, Dalyellia callvucurai n. sp. and Gieysztoria namuncurai n. sp., are described from temporary freshwater environments in central Buenos Aires Province, Argentina. The ultrastructure of the stylets of both species is also described. The new species of the genus Dalyellia is the second species of the genus found in the neotropics and the first whose stylet has been studied with scanning electron microscopy. Gieysztoria namuncurai n. sp. joins the seven species of the genus known in Argentina. The ultrastructural characteristics of the stylet place it in the Inaequales group, with complex stylets.     

The relationship between fish assemblages and the helminth communities of a prey fish, in a group of small shallow lakes

Galaxias maculatus (small puyen) is an abundant native fish distributed in lakes and rivers of the Patagonia, and it is the frequent prey of other fishes, fish-eating birds, and mammals. Previous studies have shown that it is parasitized by 33 metazoan species and that the richness and composition of the parasite communities vary between lakes. The aim of the present work was to analyze the relationship between the composition of fish assemblages and the helminth component community structure of G. maculatus . Ten environmentally similar, small, shallow lakes, belonging to the Nahuel Huapi Lake basin, were chosen because of the differences in the native fish assemblages. Parasite community structure in G. maculatus varied according to the fish assemblage of each lake. The presence of the piscivorous fish Percichthys trucha regularly produced variations in the composition and richness at the component and infracommunity levels, as well as the percentage of autogenic parasite species in G. maculatus .     

Aspects of the biology of Galaxias maculatus

The biology of three landlocked and a riverine population of Galaxias maculatus were examined in western Victoria, Australia. All systems supported reproducing populations of these fish, including Lake Corangamite which had salinities that on occasion reached 82. Spawning sites in Lake Corangamite were located in adjacent tributaries and not in the main lake as was the case for other populations. The smallest fish were found in the fresh water Lake Purrumbete and the largest in the hypersaline Lake Corangamite. The size at which 50% of the population attained sexual maturity varied across sites, with fish maturing at a smaller size in Lake Purrumbete, followed by the Merri River, Lake Bullen Merri and Lake Corangamite. Condition was higher in the freshwater Lake Purrumbete and there was no relationship between condition and temperature, conductivity, turbidity and pH; but there was a positive relationship between condition and dissolved oxygen. Length frequency analysis suggested that the majority of fishes live for a year.     

Do environmental differences between lakes in northwestern Argentinean Patagonia affect the infection of Philureter trigoniopsis (monogenea) in Galaxias maculatus (osmeriformes)?

Philureter trigoniopsis is the only parasite found in the ureters and urinary bladder of Galaxias maculatus in Patagonian Andean lakes. The dynamics of this endoparasitic monogenean were studied in Lake Gutiérrez, a body of water with scarce shoreline vegetation, where the host has an annual cycle of migration to the deep pelagic zone of the lake. To compare variations of the infection related to differences between lakes, G. maculatus specimens were sampled monthly with baited traps from September 1998 to November 1999 in Lake Moreno, which is an oligotrophic body of water with emergent shoreline vegetation and where the fish do not migrate to the deep pelagic areas of the lake. In addition, data for summer infections of P. trigoniopsis from 10 Andean Patagonian lakes that differ in aquatic vegetation, depth, and area were compared. In Lake Moreno prevalence of P. trigoniopsis showed a seasonal pattern, with 1-yr-old fish exhibiting the highest values of prevalence and mean intensity. Negative correlations between water temperature and prevalence and between age of fish and abundance were found. Our results suggest that age of fish may be the main factor structuring the distribution of P. trigoniosis in populations of G. maculatus. At the regional level the relationship between the infection and the characteristics of the lakes was also observed, with prevalence and mean intensity of P. trigoniopsis in G. maculatus higher in large deep lakes without macrophytes.     

Food and growth of hatchery-produced chinook salmon, Oncorhynchus tshawytscha (Walbaum), in landlocked Lake Purrumbete, Victoria, Australia

One-year old hatchery-produced chinook salmon were released into landlocked Lake Purrumbete, Victoria, in 1976 and specimens were recaptured at three-monthly intervals during the next two years. Examination of their stomach contents revealed that fish, particularly Galaxias maculatus , formed the bulk of the food of the salmon. Other items eaten included Amphipoda, Cladocera, Ostracoda and Decapoda (Crustacea), Odonata, Coleoptera, Diptera, Trichoptera and Hemiptera (Insecta) and Gastropoda (Mollusca). At the end of their first three months in the lake the salmon had increased 85% in length and over 670% in weight. After two years in the lake, their length was 582 mm and their weight was 2.73 kg. Growth rate was lowest in spring when the relative amount of fish in the stomach contents was at its lowest and there was a greater diversity of food types in the dict.