Oxygen requirements of zebrafish (Danio rerio) embryos in embryo toxicity tests with environmental samples

The zebrafish embryo test is a widely used bioassay for the testing of chemicals, effluents and other types of environmental samples. Oxygen depletion in the testing of sediments and effluents is especially important and may be a confounding factor in the interpretation of apparent toxicity. In order to identify oxygen levels critical to early developmental stages of zebrafish, oxygen consumption of zebrafish embryos between 0 and 96 h post-fertilization, minimum oxygen levels required by the embryos for survival as well as the effects of oxygen depletion following exposure to model sediments were determined. No significant effects on zebrafish embryo development were observed for oxygen concentrations between 7.15 and 3.33 mg/L, whereas at concentrations between 3.0 and 2.0 mg/L minor developmental retardations were observed, yet without any pathological consequences. Oxygen concentrations lower than 0.88 mg/L were 100% lethal. In the sediment contact tests with zebrafish embryos, native sediments rich in organic materials rapidly developed strongly hypoxic conditions, particularly at the sediment–water interface (0 to 500 μm distance to the sediment).