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Fish Early Life Stage (FELS) Toxicity Test

OECD 210, Regulation (EG) Nr. 440/2008 C.47


The Fish Early-life Stage Toxicity Test (FELS-Test) detects lethal and sub-lethal effects of chemicals on early life stages of fish, especially of zebrafish (Danio rerio).


The test is initiated by placing fertilised eggs in test chambers containing the dissolved test item and is continued until the control fish reach a juvenile life-stage. The FELS-Test thus allows assessment of chronic effects with respect to an important part of the life cycle of Danio rerio. The test duration is 30 days post-hatching that means 34-35 days. Lethal and sub-lethal effects are assessed and compared with control values to determine the lowest observed effect concentration (LOEC) in order to determine the (i) no observed effect concentration (NOEC) and (ii) ECx (e.g. EC50) by using a regression model to estimate the concentration that would cause a x % change in the effect measured.


The focus of evaluation endpoints is on survival, time of hatching, abnormal appearance and body length resp. weight. Other observations such as abnormal behaviour are also reported.