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In Germany the river Wupper flows through North-Rhine-Westfalia. It was originally inhabited by salmonids. But anthropogenous influences changed the fish fauna. Since then cyprinids dominate the river. Therefore physicochemical parameters were measured from 2009 till 2015 and analysed. They showed a changing temperature. Although the temperature was not exceeded for adults of Salmo trutta in the summer, it could be still defined as critical during the time of reproduction as well as during hatching. Mucus can be seen as an adequate alternative to the traditional fin-clipping for molecularbiological testing of salmonids on the fish pathogen Saprolegnia spp.. With the help of molecularbiological analysis the pathogen could be documented on nearly 50 % of the salmonids, although an infestation could not be monitiored on the fish while taking samples. A comparison of the different seasons when the samples were taken showed a change of the occurence of Saprolegnia spp. from September to May, regarding the years 2012 till 2015. Indeed no correlation between the measured temperature and the occurence of Saprolegniaspp. could be made. The natural population of S. trutta is still being stocked, which could lead to the entry of Saprolegnia spp. in the river. Potentially it can happen that morphological normal fish are already infected. Instead of using chemicals for infected fish in aquaculture the application of phytotherapeutic extracts can be seen as an alternative treatment. In vitro-experiments showed that plant extracts of Mucuna pruriens and Carica papaya could be used to inhibit the growth of the mycel of Saprolegnia ferax in the long-term.

The analysis of scales showed that the sampled Salmo trutta and Thymallus thymallus were not older than four years. Additionally these analyses showed that the oldest and biggest indiviudals were caught in the warmest regions of the river.