A project undertaken at James Cook University, and supervised by Jodie Rummer
Coral reef fishes are among the most diverse and ecologically important species in the ocean. As climate change drives rising ocean temperatures and other environmental shifts, understanding how these fishes — especially in their early life stages — cope with stress is critical for predicting the future of coral reef ecosystems.
Figure 1. the researchers test how fast the baby fish can swim on treadmills
Our project focuses on how baby coral reef fishes manage the energy they need to grow, develop, and survive.
The earliest stages of life, from fertilisation to settlement on the reef, are when these fish are most vulnerable. If they cannot adapt to changing conditions, they may not make it to adulthood, impacting entire populations.
Using a combination of field and laboratory studies, we are exploring:
How much energy young reef fishes use at different stages of development.
How their ability to swim and escape predators changes as they grow.
How their bodies (from cells to muscles) adjust to environmental changes like warmer waters.
We have measured oxygen use, swimming ability, and metabolic function in coral reef fishes at different life stages. These tests help us understand their ability to survive in warming oceans. Our team has also looked at how the tiny powerhouses inside fish cells, called mitochondria, adjust during this critical transition from larvae to juveniles.
Figure 2. baby reef fish can outswim baby fish from other habitats in the ocean
A window into adaptation:
A key part of our project is investigating how fish adapt at the genetic level. In collaboration with scientists at the Okinawa Institute of Science and Technology, we are analysing which genes are turned on or off as fish develop and experience different environmental conditions.
These genetic insights will help us determine whether some species or populations are better equipped to handle climate change than others.
The youngest athletes in the ocean:
One of our most striking findings is just how rapidly these fish develop. Within just two days post-fertilisation (dpf), their tiny hearts start beating. By three dpf, red blood cells are circulating. By four dpf, their gills — critical for breathing — already resemble adult structures, even before they hatch at around day 10. This is faster than in any other fish species studied to date. After hatching, larval reef fishes are anything but passive drifters in the ocean. We measure their swimming performance using three key metrics — critical swimming speed, endurance, and in situ observations — and in all cases, they emerge as top-tier athletes, outperforming other fish species. Their remarkable swimming ability helps them navigate the ocean, avoid predators, and ultimately find a reef on which to settle.
Figure 3.
Mitochondria — the powerhouses driving metamorphosis:
When these tiny fish finally settle on a reef, they undergo a dramatic transformation — a process driven by thyroid hormones that kickstart metamorphosis. Interestingly, within the first 24 hours of metamorphosis, the amount of mitochondria in the muscles of these fish dramatically increases. These thyroid hormones may also be triggering that surge in mitochondria, providing the energy that these fish need for this major physiological shift. Indeed, this rapid mitochondrial boost may be key to preparing the fish for life on the reef, where oxygen levels fluctuate dramatically.
Our next step is to determine which genes are switched on or off during this process, unlocking new insights into how reef fishes adapt at the molecular level.
Why does this matter? When these tiny fish settle on a reef, they undergo a dramatic transformation that requires precise physiological adjustments. Our findings suggest that this settlement period is a particularly vulnerable window in early life, with important implications for species survival under climate change.
By understanding how young fish navigate environmental challenges, we can identify species most at risk and develop conservation strategies to protect them. This research is helping piece together the intricate puzzle of how coral reef ecosystems may respond to a changing ocean and what we can do to ensure their future.