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195. A pair of Goldbelly Cardinalfish (Ostorhinchus apogonoides)


Two little Goldbelly Cardinalfish (Ostorhinchus apogonoides) are nervously seeking shelter between basalt boulders on a Mauritian reef. The Goldbelly Cardinalfish is a member of the cardinalfish family (Apogonidae) and is widespread in the Indo-Pacific region. The species occur from the Red Sea and the entire East African coast to South Africa, and in the east from the south of Japan over the Philippines and Marquesas Islands all the way to the south in Queensland, Australia, and New Caledonia.

These mouthbrooders (where the male incubates the eggs in their mouth until they hatch) are usually found in pairs but form small aggregations in certain areas.

Being typical cardinalfish, they are of average size, measuring about 8cm/3.1 inches in length.

Goldbelly Cardinalfish are among the more colourful cardinalfish species. Their flamboyant appearance, with two turquoise stripes that run over their eyes like neon tubes, breaks above the gill cover and forms small bluish spots on the rest of their bodies. Their main hues gradient between a salmon-like pink near their tail, which fades into the almost Goldfish-like orange on their main body and head. Goldbelly Cardinalfish exhibit a special feature known as the “black gut phenomenon”. In nocturnal predators like moray eels, it appears to serve to conceal bioluminescent prey in the stomach cavity from other predators so that the cardinalfish won’t light up in the dark after feeding on small prey that might have bioluminescent properties. Goldbelly Cardinalfish feed during evening hours on a variety of small fish and crustaceans/zooplankton.

Just like on land in the African Savannah, where there is a gathering of many herbivores, you could expect some predators prowling around. The grazers are “en masse” and apply the strategy of “safety in numbers”. So, where there are shoals or aggregations of small fish, always keep your eyes open for the less obvious predators such as scorpionfish, lizardfish, and frogfish species.


To reduce the number of suspended particles in the image, we’ve added noise-reducing software. This specialised software, usually a generator or an effect to upload into your editing program, has been designed to remove noise from images that were recorded under darker conditions with a high ISO setting. The software, or rather filter/generator/effect, does an excellent job in masking the little whitish flakes that formed a rather unpleasant disturbance in the shot.

Did you notice the small Decoy Scorpionfish (Iracandus signifer) in the lower left corner? The Scorpionfish is, in fact, slightly bigger than the Cardinals, but due to the angle this shot is filmed at, it creates the illusion that the Cardinals are massive compared to the Scorpionfish. This illusion is called “forced perspective” and happens when an item in the scene appears farther away, closer, larger, or smaller than it actually is. It's a way of tricking what you see by using different-sized objects and how they relate to where you're looking from. In this scene, it was done unintentionally; the bright colors and the strong illumination of the Cardinals in combination with the darker and dull appearance of the Scorpionfish are at the origins of this effect in this underwater video clip.

Filming location:

This short underwater videoclip has been filmed in Mauritius 🇲🇺

More on this topic:

For other cardinafish insights please go to these vlog posts:

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