Description: In den 1980er Jahren wurden umfangreiche Bestandsaufnahmen zur Formenvielfalt der Fischkrankheiten sowie der saisonalen und regionalen Fluktuation ihrer Befallsraten in deutschen Küstengewässern angestellt. Sowohl Formenvielfalt als auch viele der Befallsraten scheinen im Wattenmeer und insbesondere in den dortigen Flußmündungen größer zu sein als in Vergleichsgewässern. Drei “neue” Krankheitsformen werden vorgestellt: die nahrungsinduzierte Maulgranulomatose des Stints, die vermutlich durch Flexibacter-Bakterien verursachte Gelbe Pest des Kabeljaus und eine Fibrom des Steinpickers, in dem lentivirusähnliche Partikel nachgewiesen wurden. Das Schwergewicht der bisherigen Forschungsvorhaben lag auf dem Sammeln von Felddaten. Mangels experimenteller Arbeitsansätze müssen viele wichtige Fragen zur Bedeutung dieser Krankheiten daher heute noch unbeantwortet bleiben. So bleibt die Vermutung unbewiesen, daß ein Reihe von parasitenbedingten Krankheiten einen entscheidenden Beitrag zur natürlichen Sterblichkeit vor allem von jungen Nutzfischen im Wattenmeer liefert. Auch das komplizierte Wirkungsgefüge anthropogener und natürlicher Faktoren bei der Entstehung von Fischkrankheiten im Gebiet wird ohne gezielte experimentelle Arbeiten nicht aufzudecken sein. Das Auftreten von Gelber Pest, Ichthyophonus-Krankheit und lentivirusähnlichen Partikeln in Fischtumoren stellt ein beträchtliches Gefährungspotential für die deutsche Fischwirtschaft dar. Allgemein ist festzustellen, daß in Deutschland eine große Empfänglichkeit gegenüber Umweltproblemen auf dem Gebiet der Marinen Pathologie besteht. Die nationalen Forschungskapazitäten sind aufgrund anderer, meist kurzfristig angelegter Arbeitsschwerpunkte jedoch nicht ausreichend darauf vorbereitet, diese Probleme auch erfolgreich zu analysieren und zu bewerten. Als Konsequenz wird gefordert, der bislang vernachlässigten Grundlagenforschung auf dem Gebiet der Marinen Pathologie neben der reinen Datenerhebung auf See künftig eine größere Bedeutung zuzumessen. Das gilt insbesondere für experimentelle und für biochemisch- und mikroskopisch-diagnostische Arbeiten. Künftig auftretende Probleme werden nur dann rechzeitig zu bewerten und zu lösen sein, wenn sich ein ausreichend breit angelegtes und fundiertes Wissenspotential kontinuierlich weiterentwickeln kann.

Description: In April 1990, 488 marine fish, belonging to 30 species from central Philippine waters, were investigated macroscopically for the occurrence of parasites in their flesh and for anisakid nematodes in their body cavity. Twenty-four fish were found to be infected by 1 of 4 different types of parasites. Unidentified Microspora were found in 4 host species from different families. Plerocercoids of the trypanorhynchid cestode Otobothrium penetrans occurred in the flesh of hemirhamphids and belonids only. Adult nematodes of the genus Philometra were found in the garfish Tylosurus crocodilus. The only parasite found which might be transferable to warm-blooded animals was the L-III stage of Anisakis sp. from the body cavity and the muscle of Muraenesox cinereus. The risk of human infections by parasites through consumption of raw marine fish in the central Philippines therefore is considered to be low.

Description: A wide spectrum of fish hosts in the Gulf of Guinea was examined for infestation with trypanorhynchid cestodes. A total of 1341 specimens belonging to 45 species were examined. The following 9 trypanorhynchid species were identified: Callitetrarhynchus gracilis, Grillotia perelica, Nybelinia sp., Otobothrium cysticum, O. dipsacum, Otobothrium sp., Poecilancistrum caryophyllum, Ptero-bothrium sp. and one unidentified species. The pattern of occurrence of Callitetrarhynchus gracilis has been used to draw conclusions on a possible 4-host life cycle of the species, involving two obligatory teleost host fish species, small clupeids and large predatory fish. The most abundant parasite was O. cysticum which was found in 8 host fishes. In general most other species occurred in one host fish species only. The study confirms the predominance of otobothriid cestodes in the parasite fauna of tropical and subtropical teleost fish species. Since only Pseudotolithus senegalensis and Stromateus fiatola harboured flesh infestations, trypanorhynchids do not pose serious dangers to the marketability of most commercially important fish species in the area. The method of scanning electron microscopy was used to clarify the details of hooklet arrangement on the tentacular armature of some species for the first time.

Description: Commercial fish species from the east Nigerian coast were examined for external lesions and flesh parasitic infections that may affect their consumability. Altogether, 2 886 specimens from 43 species representing 34 genera were sampled. The occurrence of lymphocystis disease in the pleuronectiform Cynoglossus senegalensis is here reported for the first time from an African marine teleost. Other external lesions of fishes encountered were fin rot, granulomas, pseudotumours and ulcers with total prevalences not exceeding 1%; The following commercial fish species were infected by muscle parasites at the given prevalences: Cynoglossus browni (metacercariae, 18%, Capillaria spinosa eggs, 27%; Echinocephalus sinensis L3 larvae, 9%; Philometra beninensis, 27%); C. senegalensis (Kudoa sp., 10%; metacercariae, 87%); Pseudotolithus brachygnathus (Hysterothylacium sp. larvae, 2%); P. senegalensis (Poecilancistrum cf caryophyllum plerocercoid, 1%; Philometra beninensis, 1% P. typus (Kudoa sp., 3%); Synaptura cadenati (Echinocephalus sinensis, 12%); Stromateus fiatola (trypanorhynch plerocer-coid, 44%); Epinephelus aeneus (didymozoid trematode, 44%; Hysterothylacium sp. larvae, 6%). Capillaria and Echinocephalus, representing helminths with zoonotic potential, present low risks to publie health due to their low prevalences and the local methods of preparing fish for consumption. Apart from C. spinosa eggs in soles and trypanorhynch plerocercoids in S.fiatola, none of the other flesh parasites are likely to affect the market value of their hosts at the recorded levels of occurrence. Carcharhinid sharks influence the occurrence in the locality of most fesh-parasitic helminths for which they serve as definitive hosts. The absence of the third stage larvae of zoonotic Anisakidae common in marine fishes from many other parts of the world is related to the unavailability of suitable hosts. Compared to the results from most temperate locations where similar studies have been carried out, the present study shows remarkably low prevalences and diversity for external lesions and flesh parasites in West African marine fishes

Description: In April 1990, 488 marine fish belonging to 30 species from central Phillipine waters were examined for flesh parasitic infections that may affect their consumability. One species of hemirhamphids and 3 species of belonids harboured plerocercoids of Otobothrium penetrans Linton, 1907 (Proceedings of the U.S. National Museum33, 85–126). This is the first record of this parasite from Pacific fish species. The highest intensity of infection found was 8 in Tylosurus crocodilus. Most of the larvae were located between the dorsal spines of the vertebral column, only 32% were found in the fillets. Based on the present material we give a description of the plerocercoid stage of the species using scanning electron microscopy of the armature and morphometrical measurements. Comparison to results from earlier findings of O. penetrons by Linton (1907; 1924, Proceedings of the U.S. National Museum64, 1–114) and to O. kurisi by Shields (1985, International Journal for Parasitology15: 635–643) lead to the conclusion that the latter species is a synonym for O. penetrans.

Description: Occurrence of stomach wall granulomas in European smelt was studled at 6 locations along the German North Sea coast. Identification of larval nematodes inhabiting these granulomas is provided for the first time. Three species, isolated by pepsin-HC1 digestion, are involved: Hysterothylacium cf. cornutum, Cosmocephalus obvelatus and Paracuaria tridentata. 72% of all stomachs examined were affected. The ratio of number of granulomas to number of the 3 larval species free in the mesentery was 1:1.3. Differences in prevalences and intensities were significant among all locations. Granuloma abundance was highest in samples from the Elbe estuary decreasing in the other locations relative to their distance from the Elbe. There was no relationship between the number of larvae encapsulated on the stomach wall and the number of larval P decipjens in the musculature (r = 0.3). Host condition factor could not be related to number of granulomas. Smelt appaears to be an important transmitter of spiruroid nematode larvae to marine birds in this region.

Description: In tropical and subtropical regions of the world, jellyfish stings cause fatalities by means of venom injecting nematocysts. For nematocyst discharge an adequate combination of chemical and mechanical stimulation is required. In order to test whether skin care products can protect against nematocyst discharge, we tested two sunscreens and one lotion applied to pieces of live human skin and exposed them to Cyanea capillata tentacles. (Test specimens were collected in 1990 along the shore of Rømø, Denmark and in the Flensburger Förde.) The fine structure analysis of the cnidom of C. capillata showed a high grade of variation in shape and size. The basic distinctive characteristic for stomocnides and astomocnides, the terminal opening at the tubule tip, could not be found. The identification of spines at the basal tubule of atrichous isorhizas suggested that these should be characterized as basitrichous isorhizas. An association between nematocyst morphology and a special function such as penetration or entanglement was not observed. All nematocyst types penetrated unprotected skin. Parafilm (an inert material) and unprotected skin substrates served as controls. The discharged nematocysts on the skin and Parafilm surfaces were counted using scanning electron microscopy. The percentage of discharged nematocysts on test substance protected skin surfaces ranged from only 7.7 to 38.2%, compared to 100% on the unprotected control skin. In addition to this marked reduction in nematocyst discharge, the relatively few discharged nematocysts on protected skin showed malfunctions, and the injection of venom would have failed because the tubules of the nematocysts did not penetrate the skin. The results indicate a general possibility that human skin may be protected against nematocyst discharge of jellyfish with the application of sunscreen or lotion.

Description: In brackish water the variety of marine and freshwater parasite species is considerably reduced. The distribution in brackish water of most marine endoparasites is restricted by the salinity tolerance of their hosts, most of the parasite species are more tolerant than their hosts. The influence of salinity and temperature on nine species has been examined; first stage larvae of Contracaecum aduncum develop in 0-32‰ salinity; Cryptocotyle lingua proved to be infective at salinities down to 4‰. The greatest resistance was found in Anisakis larvae from herring Clupea harengus, which survived for more than half a year. Parasites in the fish intestines appear to be unaffected by changing water salinities, as the osmolarity in the intestines stays nearly constant. Marine ectoparasites (Acanthochondria depressa, Lepeophtheirus pectoralis) survive about three times longer than freshwater species (Piscicola geometra, Argulus foliaceus) when salinity is 16‰. High temperature increases the effects of adverse salinities on parasites. There is evidence that none of these ecto-parasitic species can develop within the range of 7-20‰ salinity.

Description: In the tidal Elbe River between Hamburg and the estuary an assessment of fish stocks and fish diseases had been carried out in 1981-1986. Despite the decline of local fisheries, the river today still carries a rich fish fauna. Smelt and shad together contribute to 70 % of the fish biomass of anchor net catches. The remaining fishery today is sustained by eel catches. In the early 1980s, 70 % of the yearly income was from the sale of consumable eel, another 20 % from stock eel. Marketing of Elbe eel for human consumption, however, is forbidden due to high levels of toxicants in the fish. A rough comparison with anchor net catches from the end of the last century does not indicate serious changes in the frequency of the dominating fish species, except for a significant decrease in ruffe and a significant increase in pikeperch. The reduced fishing mortality today is partly compensated by power plants, which together with the cooling water take considerable amounts of fish out of the river. Recent surveys revealed a !arge variety of disease types and highly pathogenic parasites, some of which occur at very high prevalences. An ecological evaluation of this finding at present is not possible due to lacking data from other streams. High disease prevalences and low nutritional condition of flounder in the central estuary are attributed to naturally fluctuating salinities, which prevent the establishment of larger zoobenthos communities which could serve as fish food. The most serious problem for fish is seen in oxygen depletion which is observed regularly every year. However, the majority of fish emigrates from the Iow oxygen zone into shallow side arms and tributary rivers or assembles downstream in front of the low oxygen zone. Efficient rehabilitation measures are seen in a reduction of discharge of fertilizing substances into the river and in a re-opening or new construction of larger side arms.