A reliable and improved methodology to expose fish in the early embryonic stage

A method has been developed to inject different substances into the yolk of fish eggs before gastrulation. Newly fertilized eggs are placed in holes in the surface of an agarose gel and the injections are made with fine glass micropipettes. The injection volume is controlled by pressure technique. The embryos are kept in the gel until hatching, where they can easily be studied under a stereo-microscope during different developmental stages, with minimized handling and therefore without disturbances. Three different species have been tested with a wide range of egg diameters. Mortality due to injection has always been lower than 1%. Due to the low mortality, different biological effects can be monitored with high accuracy and sensitivity. Therefore this methodology can be useful when investigating disturbances in reproduction as well as toxic effects at young life stages.