Until now, it was thought that fish couldn't keep warm independently like mammals such as seals or whales. The opah, or moonfish, is the first fish that has been found to have a warm heart and maintain a high body temperature, according to a new report.
NOAA Fisheries, CC BY-NC-ND
Zoological oddity —
The moonfish is a large fish and a favorite in fish markets and restaurants, making the discovery a surprise.
NOAA Fisheries, CC BY-NC-ND
Zoological oddity —
Because fish breathe by extracting oxygen from the water through gills, blood is instantly cooled to ocean temperature when it gushes out of the heart into the gills. The moonfish has evolved a unique solution: It has a special insulated network of blood vessels between the heart and gills which act as a heat exchanger, warming blood up before it leaves the gills.
NOAA Fisheries, CC BY-NC-ND
Zoological oddity —
In 10.5 C water , the opah stays a toasty 12-16 C.
Wegner et al/Science, CC-BY-NC-SA
Zoological oddity —
Mechanism can only work for large-bodied fishes with space for insulation, meaning heat loss to surroundings can be controlled.
NOAA Fisheries, CC BY-NC-ND
Zoological oddity —
The fish is a zoological oddity belonging to a group that appeared in the last 100 million years at the same time as mammals and birds evolved.
