South Korea proposes zebrafish embryo toxicity test for OECD validation

A testing method that uses zebrafish embryos — instead of mammals — to assess the neurodevelopmental toxicity of chemical substances has been proposed by South Korea's National Institute of Environmental Research and will now undergo international validation through the OECD.

The institute said Friday that a joint validation study for the zebrafish-based neurodevelopmental toxicity alternative test it proposed was unanimously approved at the 38th meeting of the OECD National Coordinators' Working Group on the Test Guidelines Programme, held recently in Paris. The study will be carried out as an official OECD project beginning Thursday.

Animal-alternative testing methods are approaches that reduce the number of animals used in experiments or minimize the suffering they undergo.

The zebrafish — also known as the zebra danio — is a tropical and subtropical freshwater fish that shares more than 70 percent of its genetic makeup with humans. Its transparent embryos make it easy to observe developmental processes, making it a valuable subject in life-science research and experimentation.

Zebrafish embryos develop into free-swimming larvae capable of movement within 120 hours of fertilization, though they cannot yet feed independently. The OECD therefore classifies zebrafish embryos within 120 hours of fertilization as non-animals, and testing methods that use them qualify as animal-alternative tests.

The method proposed by the institute exposes zebrafish embryos to chemical substances for 96 hours after fertilization, then evaluates the effects on motor and sensory nerve development and neural tissue formation to determine whether the substance is toxic.

Conventional neurodevelopmental toxicity tests using rodents require nearly 1,000 animals per substance, take up to three years, and cost more than 1 billion won ($718,000). Using zebrafish embryos cuts costs to one-fiftieth of that and accelerates toxicity screening by more than tenfold, the institute said.

The institute added that it is also pursuing international standardization efforts to have the zebrafish embryo-based neurodevelopmental toxicity test listed in the OECD guidelines.

"The neurodevelopmental toxicity alternative test we are developing will serve as a practical solution — significantly reducing the time and cost of assessing the tens of thousands of chemical substances in circulation domestically, easing the regulatory burden on industries at home and abroad, and enabling rapid toxicity screening to protect the public," said Park Yeon-jae, director of the National Institute of Environmental Research.