ZeTox – Toxicology Services


icon-fast-acute-toxicity Fish Embryo Acute Test (FET)

Fish Embryo Acute Test is designed to determine the acute toxicity of chemicals in vivo in just a few days. The use of fish embryos allows high throughput screening while providing similar predictivity to adult fish and reducing animal testing.

It is described in the OECD 236 Guideline as a test required for ecotoxicological regulatory purposes, and it is also useful to assess the safety of compounds in preclinical research.

Fish Embryo Acute Test (FET)

3Rs-aligned method for fast and high throughput acute toxicity assessment in vivo.


High experimental throughput for chemical safety assessment in vivo.

Convenient drug delivery.


Highly predictive for acute toxicity effects in humans.

Alternative experimental method to reduce animal testing while evaluating toxicity in vivo.

Applicable to a wide range of compounds regardless of the mode of action, volatility, solubility, and hydrophobicity.

Method description

Incubation of embryos with 5 different concentrations of the molecule of interest spaced by a constant factor 10 from 0 to 96 hours post fertilization (hpf). Following the OECD 236 Guideline, a convenient, rapid and inexpensive acute toxicity test has been set up.


Recording of the following four apical observations as indicators of mortality at 24 and 96 hpf:

  • Coagulation of fertilized eggs
  • Lack of somite formation
  • Lack of detachment of the tail-bud from the yolk sac
  • Lack of heartbeat

Concentration-effect curve at 96 hpf to determine the following parameters:

  • NOEC: No Observed Effect Concentration
  • LOEC: Lowest Observed Effect Concentration
  • BMD: Benchmark Dose (Lethal Concentration 10)
  • LC50: Lethal Concentration 50
Figure 1. Dose-response curves for mortality at 96 hpf after exposure of embryos to a vehicle (negative control), a toxic compound (positive control) and a study molecule that shows some toxicity.
Figure 2. Representative images of a normal (up) and a dead (down) embryo at 96 hpf.

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  1. OECD. 2013. Test No. 236: Fish Embryo Acute Toxicity (FET) Test.