At Tokyo Sea Life Park 's World of Oceans section, in the Mediterranean tank, you can sometimes see cardinalfish protecting their eggs.

The cardinalfish is a species of apogonid fish found in the temperate regions of the Mediterranean Sea and the west coast of Africa. Its striking bright red color makes it particularly eye-catching. It lives in rocky areas at depths of less than 200 meters, feeding on small crustaceans and other organisms.

If you observe cardinalfish in an aquarium, you may notice individuals with a slightly swollen lower jaw. These are males protecting eggs from predators by holding them in their mouths. Cardinalfish and other members of the cardinalfish family have a habit of the male taking the eggs laid by the female into its mouth immediately and protecting them until they hatch.

The eggs, which are initially orange, gradually darken as development progresses, a process that can be observed from the spectators.

Another fish that protects its eggs in its mouth is the fine-spotted jawfish, which is on display in the "Baja California" tank. This large jawfish, which can grow up to 40 centimeters in length, uses its distinctive large mouth to skillfully dig burrows and, like the cardinalfish, the male incubates the eggs in its mouth.

In an aquarium, it takes about 10 days for the eggs to hatch, but the male doesn't fast during that time. He sometimes places the eggs in the burrow before coming out to eat. You can also observe him moving the eggs around in his mouth to expose them to fresh seawater.

If you're lucky, you might come across fish diligently tending to their eggs.

Photo above: A cardinalfish with a swollen lower jaw.
Photo below: Fine-spotted Jawfish

[Tokyo Sea Life Park]

(May 17, 2013)