Das Projekt "Die Fische im Konstanzer See parasitierende Wuermer: Ihre saisonale und ortsabhaengige Fortpflanzung und ihre Auswirkungen auf die Fischereiindustrie" wird vom Umweltbundesamt gefördert und von Universität Tübingen, Zoologisches Institut, Lehrstuhl Tierphysiologie, Abteilung Physiologische Ökologie der Tiere durchgeführt. Objective: The ultimate goal is to produce a method which details the incidence of parasitic infestation according to location, frequency and time of the year. General Information: In order to determine whether parasitism changes the decrease in water pollution and how it affects the quality and quantity of the fish harvest, measurements will be taken from individuals of edible species in Lake Constance. The fish caught will be subjected to a quantitative and qualitative examination for ectoparasites and a histological study (especially concentrated on cestodes and cestodaria) for endoparasites. Other subjects to be studied are how parasitism can affect growth and how feeding can be responsible for infestation. Also, the possible seasonal variation in parasitic infestation will be reported. Achievements: Fish, including edible ones from 7 various locations around the upper lake of Lake Constance and the Alpenrhein, were investigated regularly for parasites. The statistical distribution of most of the commonest parasite species fitted closely to the negative binomial. Seasonal and location dependent differences relating to parasitic infestation were found with the digenean trematodes Bunodera lucipercae, Ichthyocotylurus variegatus and the cestodes Proteocephalus percae and Proteocephalus exiguus occurring seasonally. Perth and roach caught in front of Langenargen were less infested with Diplostomum spathaceum and Tylodelphys clavata than those taken from Bottighofen. Perth and roach populations from these locations do not interchange. The condition of white fish (infested with P exiguus) and of perch (invaded by D spathaceum, I variegatus, adult P percae, cysts of Trainophorus nodulosus and T clavata) was not influenced by parasites because of the great food resources. The condition of white fish caught in the Alpenrhein was worse than of those caught in the middle of the lake because the river is colder and the food is limited. Female white fish and perch were more invaded by Proteocephalus (intermediate hosts: copepods) than males during the spawning season because the food consumption of the females was higher. Cyprinids (bream, dace and roach) were less infested with Digenea (D spathaceum, T clavata) in comparison with results gained in the seventies. The decreasing eutrophication has caused a decrease of the intermediate hosts (snails). All the parasite species found are not infectious to man.