Black-finned Cardinalfish

Overview

The Black-finned Cardinalfish (Apogonichthyoides nigripinnis) is a nocturnal marine species widely distributed across the Indo-West Pacific, ranging from the Red Sea to Australia. Often found in sheltered coastal areas and offshore reefs, this fish is known for its secretive behavior, typically hiding in caves, crevices, or among weeds during the day.

Appearance

This species has a short, deep, and compressed body that typically reaches about 10 cm in length. Its coloration is generally light tan to brownish, marked by distinct dark vertical bars—one below each dorsal fin and another on the caudal base. A key identifying feature is the large, eye-like ocellus located above the pectoral fins. As its common name suggests, the pelvic fins are notably black, while the pectoral fins are lighter and other fins appear dusky or dark.

Biology & behavior

As a nocturnal predator, the Black-finned Cardinalfish emerges at night to feed primarily on zooplankton. Like many other cardinalfishes, it exhibits a unique reproductive strategy where the male acts as a mouthbrooder, carrying and protecting the developing eggs within his mouth until they are ready to hatch. These fish are often observed in pairs during courtship and spawning, and they may form small aggregations in their preferred reef environments.