Two unusually large opah, or moonfish, were caught off the waters of Antique, drawing attention because the striking deep-water fish is rarely encountered by Filipino fishermen.
The unusual catch was reported by Inquirer, which described the specimens as rare and huge warm-bodied fish found off the Antique coast. While opah are known to occur in Philippine waters, encounters with them close enough to be landed by local fishermen are uncommon.
The discovery is particularly notable because the opah is unlike most fish: scientists have identified it as the only known fully warm-blooded fish, capable of keeping its entire body warmer than the surrounding seawater.
A fish unlike almost anything else in the ocean
Opah belong to the genus Lampris and are also commonly called moonfish. Their round, laterally compressed bodies are usually silver with reddish-orange coloring, white spots and striking red fins.
Their unusual shape can make them look slow-moving, but research has shown the opposite.
NOAA scientists found that opah are active predators capable of swimming rapidly and maintaining higher body temperatures than the surrounding water. Their unusual circulatory system allows them to conserve heat as blood passes through their gills.
That adaptation is especially useful because opah spend much of their lives in cold, deep ocean waters, where maintaining body temperature can provide an important advantage.
The U.S. Fish and Wildlife Service notes that opah can keep their bodies roughly 6–8°C warmer than the surrounding water, while their specialized muscles, insulating tissue and blood-vessel network help retain metabolic heat.
Not the first unusual opah encounter in the Philippines
The Antique discovery also recalls another remarkable Philippine opah catch.
In August 2020, a fisherman in Oras, Eastern Samar, caught a 65-kilogram opah after a magnitude 6.6 earthquake struck nearby areas. BFAR officials at the time suggested that earthquake shockwaves may have disturbed the deep-water fish and contributed to its appearance in shallower waters.
The fish was identified as Lampris guttatus and was described as a deep-water species. BFAR officials said opah are present in Philippine eastern waters and may associate with highly migratory tuna, but are rarely seen.
That earlier incident demonstrates that opah encounters in Philippine waters, while unusual, are not unprecedented.
Why the Antique catch matters
The appearance of two large opah off Antique is noteworthy not simply because of their size.
Opah are oceanic, deep-water predators, and their biology makes them particularly interesting to marine scientists. NOAA research has shown that the fish’s specialized gill structure acts as a heat exchanger, allowing warm blood leaving the body to transfer heat to colder oxygen-rich blood returning from the gills.
This gives the fish an unusual physiological advantage over most other fish living in colder waters.
Research has also shown that there is more than one opah species. Genetic studies and fisheries research have identified several species within the Lampris genus, challenging the earlier assumption that opah represented a single globally distributed species.
A reminder of what remains beneath Philippine waters
The Antique catch also highlights how much remains to be documented about the country’s marine biodiversity.
Philippine fisheries references include opah among the country’s large pelagic fishes, alongside species such as tuna, marlin, swordfish and ocean sunfish.
For coastal communities, encounters with unusual species can therefore provide valuable information about what is moving through local waters—particularly when the animals are species that normally spend much of their time away from the surface.
The two opah caught off Antique may have been an unusual sight for local fishermen, but their appearance also offers another glimpse into the remarkable diversity of the Philippine seas.
And perhaps the biggest surprise is this: the fish that looks like an ordinary oversized moonfish is actually one of the ocean’s most extraordinary physiological specialists.
Accuracy note
The available sources confirm the remarkable biology of opah and document previous large opah catches in the Philippines. However, I could not independently retrieve the full Inquirer article because its page blocks automated access, so I have not invented the two Antique specimens’ weights, exact fishing location, names of fishermen, sale price, or circumstances of capture. Those details should be taken directly from the original Inquirer report before publication.
