When it comes to making its grand entrance into the world, fish embryos do not leave things to chance.

Researchers, led by Dr. Matan Golan of the Hebrew University of Jerusalem and the Agricultural Research Organization-Volcani Institute, have discovered that the hatching process of fish embryos is not a passive process. 

When the time is right, the embryo produces a neurohormone called thyrotropin-releasing hormone (Trh) in the brain which signals a specialised gland to release enzymes that dissolve the egg wall. The production of Trh is crucial. If it is not produced, the embryos remain trapped inside their eggs and subsequently perish.

In addition, the timing of the hatching is pivotal—emerging too early or too late can be fatal for the embryo. Fish embryos rely on Trh to ensure precise timing for survival.

The study, published in the Science journal, offers insights into evolution in fish and underscores the fish embryo's astounding ability to actively make decisions that improve their survival.