Parents of angsty teens have almost certainly heard this line at least once: I didn’t ask to be born.
For fish embryos, communication about their impending birth appears quite the opposite. A report in Science details how fish-in-the-making play an active role in determining their delivery.
A Fish Embryo Decides When to Hatch
Such timing is crucial to baby fish — indeed, to all egg-laying species. Controlling one’s own hatch ensures that the embryo emerges as a newborn, fully developed and ready to face the challenges of the outside world.
Earlier studies have shown that fish embryos can detect environmental conditions that favor their survival after birth. But scientists didn’t understand how that message was sent, received, and acted upon.
Researchers in Israel uncovered the chemical communication fish embryos use to signal they are ready to face the world. Think of it as a dedicated telephone line — but with hormones flowing through it, rather than sound waves.
Timing the hatch is critical for survival. Emerging too soon can lead to death, because the baby fish won’t have developed the tools necessary to deal with the outside world. Not waiting for predators to leave the area before birthing may also play a role in a newborn fish’s demise.
Read More: Isolated Female Crocodile Gives Birth Without Mating: How Is This Possible?
Releasing the Hormones
When fish embryos are ready to hatch, they place a call, basically saying “It’s all clear out there. I’m ready to go.” That call — transmitted through the release of a specialized hormone called Thyrotropin-Releasing Hormone (TRH) — sends a message from the brain to a specific gland that, in turn dissolves the egg wall, enabling the embryo to break free.
Experiments the research group performed in zebrafish showed that, without TRH, this doesn’t happen. In that case, the egg dies within the embryo. Also, TRH disappears following hatching, showing that it plays a specialized — and short-lived — role in the birth process.
There are still details to work out, though. The researchers haven’t yet pinpointed why the call gets made. They still need to identify what environmental cues initiate it, and how these inputs trigger TRH’s release.
Since many species deliver their young through eggs, the researchers next wish to examine how hormones like TRH work in these other vertebrates. They may also explore what genes these species have in common that may help produce such hormones.
Read More: Baby Elephants Move With Herd Right After Birth
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Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
