Paternal hatching care regulates the timing, synchrony, and success of hatching in a coral reef fish

In oviparous species, the timing of hatching is a crucial decision, but for developing embryos, assessing cues that indicate the optimal time to hatch is challenging. In species with parental care, parents can assess environmental conditions and induce their offspring to hatch. We provide the first documentation of parental hatching regulation in a coral reef fish, demonstrating that male neon gobies (Elacatinus colini) directly regulate hatching by removing embryos from the clutch and spitting hatchlings into the water column. All male gobies synchronized hatching within 2h of sunrise, regardless of when eggs were laid. Paternally-incubated embryos hatched later in development, more synchronously, and had higher hatching success than artificially-incubated embryos that were shaken to simulate paternal hatching cues or not stimulated. Artificially-incubated embryos displayed substantial plasticity in hatching times (range: 88 – 244 hours post-fertilization), suggesting that males could respond to environmental heterogeneity by modifying the hatching time of their offspring. Finally, paternally-incubated embryos hatched with smaller yolk sacs and larger propulsive areas than artificially-incubated embryos, suggesting that paternal effects on hatchling phenotypes may influence larval dispersal and fitness. These findings highlight the complexity of fish parental care and may have important, and currently unstudied, consequences for fish population dynamics.

Methods
Paternal hatching care data was collected using infrared video cameras. Videos were then watched to describe paternal hatching care and determine hatching duration. Larvae that hatched from artificially-incubated stimulated and artificially-incubated not-stimulated treatments were collected every 8hrs, enumerated, and photographed. ImageJ was used to measure the total length, body depth, yolk sac area, and propulsive area of larvae from photographs. All statistical analyses were completed using R version 4.1.0.