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SUMMARY The relationship between premigratory gill Na+/K+-ATPase activity, determined at two dates during spring, and future migratory behaviour was investigated using non-lethal gill biopsies and PIT-tagging in wild brown trout (Salmo trutta) from two tributaries. No significant relationship between future migratory strategy(individuals eventually becoming migrants or residents) and gill Na+/K+-ATPase activity was found in late February–early March. By contrast, in mid-April, a highly significant logistic regression equation identifying the migratory strategy in 93% of the 75 individuals was obtained. The ability of this regression model from the tributaries to predict future migratory behaviour in an independent group of trout caught in early April in the mainstream was evaluated. A threshold probability of migration was used to predict the behaviour of the mainstream individuals as either future migrants or residents. The maximum percentage of correct predictions of future migratory behaviour in mainstream fish was observed at threshold probabilities between approximately 0.15 and 0.45(corresponding to threshold gill Na+/K+-ATPase activities between 2.7 and 3.7 μmol ADP mg–1 protein h–1), with an average of 91% of the predictions being correct. The present study shows that a non-lethal premigratory biochemical measurement can successfully select individual brown trout with high probability of migration.

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Chemical UV-filters are used in sun protection products and various kinds of cosmetics. The lipophilic chemical UV-filter 3-benzylidene camphor was investigated for its capability to cause vitellogenin induction, possibly via oestrogen receptor binding, in a well-established in vivo fish assay (juvenile rainbow trout, Oncorhynchus mykiss, vitellogenin ELISA). A clear relationship was demonstrated between the dose of injected 3-benzylidene camphor and the concentration of plasma vitellogenin with a 10 5 -times induction from 68 mg 3-benzylidene camphor /kg/injection and above compared to the control vitellogenin level. The relationship between the injected dose of 3-benzylidene camphor and the percent of responding fish (vitellogenin) was evaluated by logistic regression analysis and effective dose-values (ED-values) were determined. ED 10 , ED 50 and ED 90 of 3-benzylidene camphor after 6 days (2 injections) were 6.4, 16 and 26 mg/kg/ injection, respectively. These ED-values place 3-benzylidene camphor among the more potent xenooestrogens discovered to date and necessitates investigations on the distribution, concentration, persistence and bioaccumulation of 3-benzylidene camphor and other UV-filters in nature.