Description: Eleven fish species from the Weddell Sea (Antarctic) were examined for infestation with anisakid nematodes. Two species of the genus Contracaecum and the sealworm Pseudoterranova decipiens were isolated from the liver and the body cavity of fish affected. Only two specimens of P. decipiens (1.4%) partly invaded the belly flaps. The following fish species were infested by P. decipiens at the given prevalences: Cygnodraco mawsoni (74.4%), Trematomus scotti (23.2%), Pagetopsis maculatus (10.0%), Cryodraco antarcticus (7.1%), Trematomus lepidorhinus (3.0%), and Dolloidraco longedorsalis (2.7%). All of these, except Trematomus scotti, are new host records. Chaenodraco wilsoni, Chionodraco myersi, Gerlachea australis, Racovitzia glacialis and T. eulepidotus were not infested. The reasons for low prevalence and intensity of infestation are seen in the difficulties of P. decipiens in completing its benthic life cycle in the Weddell Sea environment, in the absence of shallow coastal waters due to the floating shelf-ice. Cygnodraco mawsoni is a crucial intermediate host, without which completion of the parasite life cycle might not be possible. In order to clarify the taxonomical position of Antarctic Pseudoterranova, morphological comparisons with specimens of P. decipiens from the German and Norwegian coast were made using scanning electron microscopy. Results revealed no differences; hence, all specimens studied belong to the same species P. decipiens.

Description: The infestation of Weddell seals and several fish species by the anisakid nematodes Contracaecum osculatum and C. radiatum was compared. Nematode numbers in Weddell seal stomachs ranged from 30 560 to 122 640. Third stage larvae from seals and fish were separated into a short and a long type. The short type was related to C. radiatum and the long type to C. osculatum. The short type was more abundant in pelagic fish species, whereas the long type prevailed in benthic fish species. Fish-feeding channichthyids Cryodraco antarcticus and Chionodraco myersi seemed to play an important role as paratenic hosts for the third stage larvae of both Contracaecum species. Different advantageous and detrimental features of a benthic versus a pelagic life cycle under high Antarctic ecological conditions are discussed. Varying abundance of the two nematode species in hosts may be controlled by differences in their life cycles, which follow either a pelagic or a benthic food web. Crucial importance is thus given to the local availability of pelagic versus benthic food resources for Weddell seals.

Description: Investigations on the occurrence of trichodinid ciliates from fish caught in the Kiel Bight and Kiel Fjord (western Baltic Sea) were carried out between September 1996 and March 1997. Smears of the gills, fins, and skin of 120 Gadus morhua and 92 Platichthys flesus caught by fish traps and trammel nets revealed the presence of trichodinid ciliates. According to the fish species and locality, different prevalences and densities of trichodinid ciliates were found. Fish caught in the Kiel Bight revealed a lower prevalence of trichodinid ciliates on their gills (P. flesus 74.2%, G. morhua 3.8%) in comparison with fish of the same species and size caught in the Kiel Fjord (P. flesus 75.0%, G. morhua 26.2%). In both areas, P. flesus was more heavily infested than G. morhua. Seasonal changes in the prevalence of infestation of P. flesus between autumn and winter in the Kiel Fjord are proposed to be linked to an increase in bacterial biomass during winter. The fish ecology in combination with the total number of bacteria in the fish environment is discussed as an important factor influencing the abundance of trichodinid ciliates. The present data suggest the use of trichodinid ciliates as an indicator for eutrophication in brackish-water environments.

Description: Blue mussels (Bivalvia) potentially accumulate Vibrio spp. and can transfer these ­pathogens into the consumer. Earlier studies dealt with the existence of V. para­haemolyticus in natural environments but no examinations under laboratory con­ditions exist on the influence of temperature onto accumulation and persistence in blue mussels under low salinity environments. The aim of this study was to design a reliable and practicable methodology to examine the presence of V. parahaemo­lyticus in blue mussels from the Baltic Sea and possibilities for decontamination. A static design was chosen, estimating the influence of temperature onto contami­nation and clearance kinetics. Blue mussels accumulated a similar amount of V. parahaemolyticus during 24 h with no significant difference at the chosen temperatures of 5, 10 and 20 °C. After transfer into clearance tanks, the numbers of bacteria ­decreased in all mussels for 72 h, but the amounts differed significantly between 5 °C to 10 °C and 10 °C to 20 °C. Highest reduction from initial 4.84x107 cfu/mg to 1.16x105 cfu/mg (72 h) was observed at 10 °C (about 0.2 % of initial value). The Baltic Sea offers opportunities for blue mussel production, especially in the context of ­Integrated Multi Trophic Aquaculture to reduce environmental impact of fish aquaculture. In the case of mussel infection, a clearance bath for 72 h under 10 °C can prevent possible transfer of V. parahaemolyticus into the consumer.

Description: The scolices of six different trypanorhynch species--Heteronybelinia alloiotica (Dollfus, 1960), Pseudolacistorhynchus noodti Palm, 1995, Otobothrium cysticum (Mayer, 1842), O. penetrans Linton, 1907, Poecilancistrum caryophyllum (Diesing, 1850), and Prochristianella hispida (Linton, 1890)--were examined for surface morphology and the occurrence of sensory receptors. Filamentous microtriches with different internal ultrastructural features were found. Acerosate, hook-like, and spiniform microtriches were detected on the surface of the tentaculariid H. alloiotica. Their internal structure clearly differed from that of pectinate microtriches observed in the other five trypanorhynch species lacking a basal and a junctional region. All pectinate microtriches had the same general architecture, independent of the number of digitiform processes. All trypanorhynchs studied harbored ciliated sensory receptors within the tegument. Even though sensory receptors were scarce in H. alloiotica, they were more abundant in the lacistorhynchid P. noodti and the otobothriids P. caryophyllum and O. penetrans, which exhibited two, six, and three kinds of receptors, respectively. Bothridial pits in O. penetrans and O. cysticum were invaginations of the bothridial surface, being characterized by the lack of sensory receptors and the presence of characteristic microtriches. These differed from other microtriches in that they were larger and had a base consisting of a widely enlarged matrix. The occurrence of different kinds of microtriches and sensory receptors within trypanorhynch cestodes is summarized, and the meaning of these surface structures and of bothridial pits as characters within future trypanorhynch classification is emphasized.

Description: A total of 386 Macrourus whitsoni from Antarctic waters were examined for ecto- and endoparasites. Sixty-five M. whitsoni collected near Halley Bay (Weddell Sea) and 321 specimens from the continental slope off King George Island (South Shetland Islands) were studied for sphyriid copepods directly after being caught. A subsample of 25 specimens from the Weddell Sea and of 9 specimens from King George Island were studied for the presence of other metazoan parasites. Twenty-two species were found, including one myxozoan, six digeneans, one monogenean, three cestodes, seven nematodes, one acanthocephalan and three crustacean species/taxa. While Auerbachia monstrosa and Capillaria sp. are reported for the first time from around the Antarctic, the other parasites have been recorded earlier in the Southern Ocean. Many parasite species found have a wide zoogeographical range and a low host-specificity. The parasite fauna of M. whitsoni revealed several similarities with its congeners M. carinatus and M. holotrachys from Antarctic and sub-Antarctic waters. This can be explained by a wide host range of many macrourid deep-sea parasites, together with an overlap in distribution patterns of their hosts. Other supporting factors are host migration and a close phylogenetic relationship between the hosts, which enable the parasites to infest all three macrourids. Eight new host and 14 new locality records are established.

Description: The present study provides further data on the occurrence of Pseudoterranova decipiens in fish from two different sampling sites in the Antarctic. A total of 690 fish belonging to 33 species from the eastern Weddell Sea and 322 fish belonging to 12 species from the South Shetland Islands were examined. Altogether, 23 fish species were found to be infested and 11 new host records could be established. P. decipiens occurred at a water depth of between 80 and 820 m. Chaenocephalus aceratus and Notothenia coriiceps from the South Shetland Islands were the species with the highest prevalence (95%) and intensity (2-194 and 1-121, respectively) of infestation. Both are transport hosts, which mainly feed on benthic nototheniid fish species and accumulate the nematodes. Bathypelagic, pelagic, or mainly euphausid feeding fish species were only lightly infested, if at all. This demonstrates the benthic life cycle of P. decipiens in the Antarctic. The preferred site of infestation was the body cavity and the liver; no specimen could be isolated from the fish musculature. This might be explained by the low water temperatures. The infestation of fish from the Weddell Sea was distinctly lower than that of fish around the South Shetland Islands. Besides possible differences in final host populations at the two localities studied, the loss of eggs and larvae under the eastern Weddell Sea shelf ice and over the continental slope and differences in the availability of the first intermediate and macroinvertebrate hosts led to a lower level of infestation. Another role, although nondecisive, may be played by the reduced time of development and infectivity of eggs and larvae, respectively, in the extremely cold waters of the Weddell Sea. P. decipiens is not a rare but, rather a well-established parasite of the Antarctic fauna, which demonstrates the ability of this cosmopolitan species to complete its life cycle even under conditions of subzero temperatures.

Description: On the basis of the tentacular armature, surface ultrastructure, and morphological measurements of plerocerci obtained from the musculature of butterfishes (Stromateidae), we corroborate an earlier proposal that Otobothrium crenacolle, a commonly reported trypanorhynch cestode from the northwestern Atlantic coast, is a junior synonym of O. cysticum. This action exemplifies at least an Atlantic Ocean and Indian Ocean distribution for O. cysticum. The infection in commercially important butterfishes shows that an otobothriid trypanorhynch may heavily infect fish flesh and influence the market value of some fish species yet also be restricted to the body cavity of other fish intermediate hosts. Infections of O. cysticum in the flesh of Peprilus burti (Gulf butterfish) and P. alepidotus (harvestfish) in the Gulf of Mexico has varied annually since 1970, with samples ranging in prevalence between 20% and 100% and in mean intensity between 1 and 3,500 or more plerocerci per fish. Comparative infections in P. burti from the Gulf of Mexico and P. triacanthus (butterfish) from the Atlantic Ocean demonstrate a present geographic difference in infections. The prevalence and mean intensity in 4 collections of butterfishes ranged from 9% to 98% of the fish and from 1 to 678 plerocerci in a subsample of tissue, respectively, with prevalent and heavy infections being observed in the Gulf of Mexico fish and relatively few individuals being infected with few worms in the Atlantic fish. A slight host response in the butterfishes involving some fatty infiltration and inflammatory infiltration was associated with the metacestode. In some larger fish, encapsulations were yellow, and in a few cases, worms had degenerated. This finding and an increase in intensity with fish weight suggest a continual accumulation of the worms in association with little host resistance.

Description: Fifty specimens of Notothenia coriiceps caught in Potter Cove, King George Island, were examined for ecto- and endoparasites. Of the 22 parasite species found, 18 were helminths, 2 were hirudineans and 2 were crustaceans. The isopod Aega antarctica and an unidentified hirudinean are reported for the first time from this fish host. Dominant parasites were the adults of Aspersentis megarhynchus, the invasive stage of Corynosoma spp. (cystacanth) and the adults of Macvicaria pennelli, with respective prevalences of infestation of 94, 76 and 74%. The preferred sites of infestation were the pylorus and intestine, where five different larval (nematodes and cestodes) and eight adult (digeneans and acanthocephalans) parasite species were found. No adult nematodes and cestodes were found and no parasites could be isolated from the musculature. The results of the present study are related to previous findings on the parasite fauna of N. coriiceps. The comparison implies a high parasite diversity in this benthic Antarctic fish species. Most parasites found appear to have a wide range of distribution within Antarctic waters together with a low host specificity. Besides its role as final host for several species of trematodes and acanthocephalans, N. coriiceps serves as transmitter of parasite larvae to piscivorous birds and seals. It is concluded that the parasite fauna in Antarctic fish species provides important insights into the different habitat use and trophic relationship of their fish hosts.