A Closer Look at Clownfish Adaptation
A recent study observed 67 breeding pairs of wild clownfish in Kimbe Bay, Papua New Guinea, documenting their distinctive markings and measuring them before releasing them back into the water. The research, conducted between February and August 2023, coincided with the occurrence of the world’s fourth global coral bleaching event. The team monitored the clownfish’s body size on a monthly basis and recorded the temperature around their individual anemones every four to six days, later analyzing the gathered data.
“Individual fish can shrink in response to heat stress.”
Credit: Morgan Bennett-Smith
The findings revealed that 101 out of 134 clownfish experienced shrinkage at least once due to heat stress. Shrinking enhanced their chances of survival to 78 percent, compared to the 33 fish that did not exhibit size reduction. Notably, the study found that within breeding pairs, the dominant and subordinate fish showed distinct growth ratios; pairs that shrank together had higher survival rates during heat waves.
“We were amazed to observe size reduction in these fish, which led us to repeatedly measure each individual over five months,” stated Versteeg. “Ultimately, we discovered that this phenomenon was quite common in the population. It was surprising to see how swiftly clownfish can adapt to a changing environment, demonstrating remarkable flexibility in regulating their size in response to heat stress as an effective survival strategy.”
Although Versteeg and the team have yet to determine the specific mechanisms behind this shrinkage, they propose that neuroendocrine pathways triggered by thyroid hormones might contribute, as these hormones influence growth. This adaptive response could also be a way for the fish to adjust to their changing metabolic requirements. However, there are potential drawbacks; while size reduction may enhance survival, it could lead to decreased birth rates as well.
“Our research indicates that individual fish can shrink in response to heat stress, influenced by social dynamics, and that such shrinkage can improve survival odds,” remarked senior author Theresa Rueger, also from Newcastle University. “If this shrinking behavior is common across various fish species, it might explain the declining sizes observed in many fish populations, warranting further investigation in this domain.”
Science Advances, 2025. DOI: 10.1126/sciadv.adt7079 (About DOIs).
