Recent research has shed light on the impacts of ocean warming on fish size reductions in some of the world’s hottest coral reefs. The debate surrounding the impact of ocean warming on fish and fisheries has been ongoing, with leading theories projecting limited adaptive capacity for tropical fishes and significant size reductions by 2050.

Researchers have utilized the Persian/Arabian Gulf as a natural laboratory for studying the effects of ocean warming on fish size. In this region, where species have endured summer temperatures exceeding 35.0°C for over 6000 years, fish are found to be 14-40% smaller at their maximum size compared to fish in cooler locations.

The study focused on two fish species, Lutjanus ehrenbergii and Scolopsis ghanam, comparing individuals from reefs inside and outside the Persian/Arabian Gulf across different temperature ranges. The results revealed that these species exhibited lower-than-expected increases in basal metabolic demands and a right-shifted thermal window, enabling them to maintain oxygen supply and aerobic performance even at temperatures as high as 35.5°C.

The findings challenge traditional theories that attribute size reductions to oxygen limitations, suggesting instead that a mismatch between energy acquisition and demand is the primary driver of size reductions in fish. The data support a modified resource-acquisition theory, indicating that smaller individuals are evolutionarily favored under elevated temperatures.

This research provides valuable insights into how ocean warming can lead to species-specific size reductions and highlights the importance of understanding the adaptive mechanisms that enable certain fish species to thrive in warming ocean environments. By studying fish populations in extreme conditions, scientists can gain a better understanding of the potential impacts of climate change on marine ecosystems.