Effect of age on the susceptibility of zebrafish eggs to industrial wastewater

Toxic effects of 40% (v/v) and 60% (v/v) concentrations of wastewater from the industrial sector of chemical production on eggs of the zebrafish (Danio rerio) were investigated. Significant poisonous effects could be registered in test solutions containing 40% wastewater for eggs up to 0.5 h of age. Solutions containing 60% wastewater affected the mortality of the exposed eggs up to 1 h of age. Earlier stages were more sensitive to industrial wastewater than later stages. The differences in susceptibility must be ascribed to the ontogenetic stage of the eggs at which the experiment was started and to differences in the chorion permeability. The chorion is less permeable after hardening and works as a barrier to detrimental wastewater contents. This circumstance explains the higher viability of zebrafish eggs at the age of >1 h. When using early stages of the zebrafish for ecological risk estimations, the eggs should, at best, not exceed the age of 0.5 h.