Summary
After its standardisation at the national level in Germany (DIN
38415-6, 2001; DIN, 2001), the 48 h sewage testing assay with zebrafish
(Danio rerio) embryos has been submitted for standardisation
to ISO. As an alternative to the conventional acute (96 h)
fish test, a modified fish embryo test will be submitted to the
OECD for chemical testing in late 2005. For this, a protocol originally
designed for zebrafish was adapted to fit also the requirements
of other OECD species, namely medaka (Oryzias latipes)
and fathead minnow (Pimephales promelas). Results document
that the transfer of the protocol is possible with only minor modifications.
Data obtained from embryo tests with the three species
are comparable. Statistical analysis of existing zebrafish embryo
toxicity data resulted in the conclusions (1) that there is a reliable
correlation between the fish embryo test and the acute fish test,
(2) that the confidence belt of the regression line was relatively
small, but that the prediction range was relatively wide. The regression
thus seems appropriate to describe the relationship
between acute fish and embryo LC50 with good confidence, but is
less appropriate as a prediction model.
Investigations into oxygen requirements of zebrafish embryos reveal
that they adapt to a broad range of oxygen levels and survive
at concentrations of 2 mg/l without malformations. Zebrafish embryos
can thus be exposed in very small toxicant volumes (100
μl), which is of particular interest for the testing of metabolites.
Dechorionation studies with 48 h old zebrafish embryos indicate
that the barrier function of the chorion increases with the
lipophilicity of the test compound. Finally, examples are given as
to how additional endpoints can be incorporated into the fish
embryo test protocol to extend its scope, e.g. to sediment toxicity
assessment or genotoxicity and mutagenicity testing.