The first life-altering step for a fish is leaving the safety of its nest and hatching into the big unknown. Researchers have long been fascinated with determining how embryos can discern when to hatch based on subtle cues from their environment. For the tiny neon goby (Elacatinus colini), the fathers decide for them, spitting the young from the seclusion of the nest when they feel the time is right. These small fish live in cylindrical sponges in the Belizean barrier reef, and the embryos are cared for by their fathers for up to a week before hatching. Armed with this knowledge, John Majoris from Boston University, USA, and a team of researchers from Humboldt University, Germany, and the University of Texas at Austin, USA, were interested in whether neon goby fathers can regulate the timing of their youngster's hatching and whether this translates to changes that would benefit the progeny once they hatched.
Majoris and his team went diving off the coast of central Belize to collect neon goby adults before shipping them to the lab at Boston University. To figure out whether the fathers regulated the timing of hatching, the team coaxed the breeding pairs to spawn. Ingeniously, the team was able to create transparent acrylic shelters that resembled the cylindrical sponges that the neon gobies naturally live in, allowing them to monitor the fathers’ behavior before the embryos were due to hatch, and to video the hatching. When neon goby embryos were incubated with their fathers present, they hatched later, more in unison, and in a greater proportion than those incubated without their fathers present. This means that even though the embryos that were incubated with their fathers had the ability to hatch, they waited until the fathers gave their go-ahead to do so. The ability to hatch more in unison may also give neon goby larvae a leg up to life outside the nest by helping them deal with predators as they hatch.
The researchers also found that, after hatching, the embryos that developed with their fathers were bigger and more developed than those that did not, which can translate into hatchlings that are better suited to swimming and feeding. These fathers can directly influence their youngster's ability to survive because they can recognize optimal environmental conditions more easily than the embryos. This makes sense as the embryos usually develop in nooks and crannies of the reefs, making it difficult to discern the right time to leave the nest. This crucial decision by neon goby fathers can help their youngsters have an advantage after hatching, proving that fathers know best.