ZeTox – Toxicology Services


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

Fish Embryo Acute Test is designed to determine acute toxicity of chemicals on embryonic stages of fish. 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.


High throughput screening of compounds.

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

Highly predictive for acute toxicity effects in humans.

Method description

Incubation of embryos with 5 different concentrations of the molecule of interest spaced by a constant factor 2 from 0 to 96 hours post fertilization (hpf). Assay performed according to the OECD guideline 236.


Recording of the following four apical observations as indicators of lethality at 24, 48 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

Determination of the following parameters at 96 hpf:

  • LC50: Lethal Concentration 50
  • NOEC: No Observed Effect Concentration
  • LOEC: Lowest Observable Effect Concentration
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.


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