How seahorses change colour, one habitat at a time
Published in Zoology & Veterinary Science and Anatomy & Physiology
Seahorses are often celebrated for their unusual shape, but another remarkable feature tends to receive less attention: their ability to alter body colour in response to their surroundings. For animals that spend much of their lives anchored to seagrasses, corals, and other coastal structures, blending into the background can be an important part of staying unnoticed. A new study published in Reviews in Fish Biology and Fisheries takes a closer look at how this process unfolds and what may be happening behind the scenes.
Using the lined seahorse (Hippocampus erectus), the authors exposed individuals to different background environments and monitored their appearance over time. Rather than changing colour within seconds or minutes, as seen in some marine animals, the seahorses gradually shifted from dark coloration to yellow, red, or grey forms over several days. Most colour transitions occurred within the first five days, after which the response approached a plateau.
To better understand the biological basis of these changes, the researchers combined behavioural observations with microscopy, comparative genomics, and gene expression analyses. Their results suggest that colour shifts are associated less with the production of new pigment and more with changes in the distribution and organisation of existing pigment granules within pigment cells. Dark individuals showed densely distributed melanophores, whereas lighter colour morphs exhibited reduced pigment coverage and more aggregated pigment granules.
Visual input
The study also explored the possible role of vision. In a separate experiment, seahorses whose eyes were covered did not show detectable colour changes during the 72-hour observation period. The authors are careful to note the limitations of this experiment and do not interpret it as definitive proof. Nevertheless, when considered alongside the genomic and transcriptomic data, the findings are consistent with a possible contribution of visual input to background-associated colour change.
One of the most interesting aspects of the work is its broader evolutionary perspective. By comparing seahorses with colour-changing reptiles and amphibians, the researchers identified shared genetic signatures linked to visual perception, neural signalling, cytoskeletal remodelling, and pigment transport. Although the mechanisms differ among groups, the study suggests that similar biological pathways may repeatedly contribute to adaptive colour modulation across vertebrates.
Beyond the evolutionary questions, the findings may also be relevant for aquaculture and the ornamental fish sector. The authors propose that carefully designed visual environments, including substrate and background colour, could help influence body coloration in captive seahorses while working with their natural behavioural responses. At the same time, the study offers a reminder that camouflage is not simply a matter of colour. It may depend on an intricate interaction between perception, physiology, and the environment itself.
Author's note: I used Microsoft Copilot to assist in creating this post.
Image: shellac, CC-BY 2.0
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Reviews in Fish Biology and Fisheries
Reviews in Fish Biology and Fisheries is an international journal that publishes original and review articles on various aspects of fish biology, fisheries, and aquaculture.
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Sustaining Life Below Water: Conserving, managing, and protecting our marine and freshwater resources
In support of the UN Sustainable Development Goal SDG14 we are calling for submissions for this new collection on Sustaining Life Below WaterPlastic waste, overfishing, ocean acidification, increasing eutrophication are some of the major threats endangering our oceans, rivers and lakes. With this collection we aim to create a cross-disciplinary home for research articles, perspectives, and emerging topics addressing the conservation and sustainability of the use of our marine and freshwater resources. By putting scholarship supporting this UN Goal in the spotlight we hope to increase the scientific knowledge and awareness of the targets and indicators set by the UN Goal such as reducing marine pollution, strengthening resilience, restoring coastal ecosystems, minimizing the impacts of ocean acidification, reducing destructive fishing practices, providing access for small-scale fishers to marine resources and markets and more.
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