The humble sapsap has a surprising ability to make sounds when caught

A freshly caught sapsap may have one last surprise for the fisherman who pulls it out of the water: a faint squeak or grunt.

Known in English as slipmouth or ponyfish, sapsap is one of the most familiar small fish in Philippine wet markets. Its flat, silvery body, delicate white flesh, and relatively affordable price have made it a favorite in Filipino kitchens.

But beyond its popularity as an everyday meal, this unassuming fish belongs to a family with some remarkable biological features.

Sapsap belongs to the family Leiognathidae, whose members have highly protrusible mouths that extend outward like tiny tubes to suck up food from the seabed. This unusual anatomy explains the English name slipmouth.

Even more fascinating is the family’s ability to produce light. Ponyfishes possess specialized organs containing bioluminescent bacteria, allowing them to emit a glow that helps camouflage their bodies from predators swimming below.

But what about the reported grunting sound?

Some fishermen describe freshly caught sapsap producing faint squeaks or grunts. While many fish species are known to produce sounds by vibrating their swim bladders or rubbing specialized skeletal structures together, the precise sound-producing mechanism in sapsap has not been firmly established.

From the sea to the Filipino table

Sapsap’s delicate, mildly sweet flesh makes it particularly suited to traditional Filipino cooking.

Perhaps the most popular preparation is pritong sapsap, fried until golden and crispy, with the smaller fins and bones sometimes becoming crunchy enough to eat. It is commonly paired with vinegar, tomatoes, and steaming white rice.

Another favorite is paksiw na sapsap, simmered in vinegar, garlic, ginger, and peppercorns. Its naturally tender flesh absorbs the sharp, savory flavors beautifully.

In some households, sapsap is prepared as pinangat, gently cooked with tomatoes and souring ingredients such as kamias. It can also be simmered in coconut milk for a richer ginataang version.

Dried and salted sapsap, sometimes sold as potpot, is another familiar delicacy, especially when fried crisp and served with garlic rice for breakfast.

And while sapsap remains a relatively inexpensive source of protein, its value extends beyond the dinner table.

This modest fish, capable of producing its own light and equipped with an extraordinary extendable mouth, is proof that some of the ocean’s most fascinating creatures are also among the most familiar ingredients in Filipino kitchens.