Contrasting associations between breeding coloration and parasitism of male Arctic charr relate to parasite species and life cycle stage.

Conspicuous carotenoid ornamentation is considered a signal of individual "quality" and one of the most intensely studied traits found to co-vary with parasitism. Since it has been suggested that only "high quality" individuals have enough resources to express excessive sexual ornaments and resist parasites, current theory struggles to explain cases where the brightest individuals carry the most parasites. Surprisingly little emphasis has been put on the contrasting routes to fitness utilized by different parasite species inhabiting the same host. Using Arctic charr (Salvelinus alpinus) as model species, we hypothesized that skin redness and allocation of carotenoids between skin and muscle (redness ratio) will be positively and negatively associated with parasites using the fish as an intermediate and final host, respectively. Both pigment parameters were indeed positively associated with abundances of parasites awaiting trophic transmission (Diplostomum sp. and Diphyllobothrium spp.) and negatively associated with the abundance of adult Eubothrium salvelini tapeworms. These empirical data demonstrate that contrasting associations between carotenoid coloration and parasite intensities relates to the specific premises of different parasite species and life cycle stages.

[Study of the monogenean family Tetraonchidae Bychowsky, 1937 by the scanning electron microscopy].

Hitherto data on the morphology of Tetraonchidae and their eggs obtained with scanning electron microscopy (SEM) were absent in the literature. In the present paper results of SEM study of two genera of Tetraonchidae, Tetraonchus and Salmonchus, are given. Fine morphological traits of eggs, larvae, and definitive individuals of Tetraonchidae, as well as patterns of their attachment to host gill, were established for the first time. A deep penetration of the worms into the branchial epithelium of the host was shown.

Geographical distribution of Metagonimus yokogawai and M. miyatai in Shizuoka Prefecture, Japan, and their site preferences in the sweetfish, Plecoglossus altivelis, and hamsters.

Sweetfish, Plecoglossus altivelis, obtained from 18 rivers in Shizuoka Prefecture were examined for metacercarial infection of 2 flukes, Metagonimus yokogawai and Metagonimus miyatai. The infection rate and density of metacercariae in the fish were higher in eastern and western regions than in central region of the prefecture. After infection of hamsters with metacercariae derived from the scale, 98.7% of the adult worms obtained from the intestine was found to be M. miyatai. Conversely, from infection with metacercariae from the flesh, 90.0% of the worms was M. yokogawai. Since the worms had no exclusivity in the tissues, we conclude that the flukes have location preference with the former primarily preferring the scale, and the latter the flesh. Fish from two rivers located in adjacent areas in the western region had relatively a higher ratio of M. yokogawai in the scale relative to other rivers, suggesting an intraspecific genetic variation due to geographical isolation. On examination of adult worms in the hamster's intestine, M. yokogawai was mainly located towards the anterior part of the intestine, unlike M. miyatai, suggesting that in mammalian host too, the parasites have site preference.

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 per cent) and A. apophalliformis (prevalence 30-54 per cent) than for C. corderoi (prevalence 6-8 per cent). 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.

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.

Parasitation with Pseudoterranova decipiens (Nematoda) influences the survival rate of the European smelt Osmerus eperlanus retained by a screen wall of a nuclear power plant.

A total of 354 adult European smelts Osmerus eperlanus (L.) were tested for their ability to survive the screen system of the cooling water inflow of a power plant. With increasing number of musculature parasitic third-stage larvae of Pseudoterranova decipiens, the survival rate of O. eperlanus decreased while the total number of externally visible injuries as well as the number of seriously injured specimens increased. The results indicate that even a single specimen of P. decipiens influences resistance and stamina and affects overall mortality of 7 to 20 cm long smelts. The initial effect of the parasites is to reduce swimming speed of infested fish, which leads to more frequent contact of these fish with the fine meshed screen of the cooling water inlet before they are removed by the automatic cleaning system. If the separated fishes are returned to the main stream, it becomes apparent that the cooling water inflow selectively reduces the number of living parasitised smelt in the area. Thus, the number of parasitic third-stage P. decipiens larvae in the local smelt population which are able to complete their life-cycle is also reduced. P. decipiens makes infested smelt more susceptible to negative anthropogenic influences such as cooling water intake or trawl fisheries.