Revision of the Fish Acute Toxicity Testing Guideline OECD 203

25th June 2019

The revised guideline describes how to perform acute toxicity tests with fish in more detail, for example the use of alternative methods for testing and range-finding and demands on analytics as well as statistical analysis.

The change of the acclimatisation and exposure period of rainbow trouts from 13-17°C to 10-14°C is one significant aspect. Another important adaptation is the smaller length range for several fish species in comparison to those stated in the earlier version of the guideline. For example, the length range for the zebrafish Danio rerio decreased from 1-3 cm to 1-2 cm. Furthermore demands regarding loading rates increased from 1 g/L to 0.8 g/L and for flow-through testing a loading rate of 0.5 g/L is defined. An advantage is the reduced time for settling and acclimatisation prior the start of an experiment which decreased from 12 to 9 days. Assessment of the well being of the fish and of fish symptoms need to be performed two times a day now, resulting in much more effort.

Animal welfare aspects are emphasised. The number of fish required is reduced by abandoning the water control in case of solvent use; the solvent control is deemed sufficient in such cases. The concept of the Threshold Approach (OECD 2010) may be applied. An exclusion of moribund fish has not been included, but enhanced recording of abnormalities, as suggested in the revised document, should improve the prediction of moribundity and enable the implementation in a future version.

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