Yellowmouth Moray in Mauritius — Gymnothorax nudivomer

The Yellowmouth Moray (Gymnothorax nudivomer), known in French as the Murène à bouche jaune, is one of the most visually striking moray eels found in the Indo-Pacific region — and Mauritius is fortunate to host a healthy and common population of this impressive species. Characterised by its distinctive bright yellow interior mouth and throat that contrast sharply with its brown, white-spotted body, this eel is instantly recognisable to experienced divers and marine enthusiasts exploring Mauritian coral reefs.

Physical Characteristics

Growing up to 180 cm in length, the Yellowmouth Moray is one of the larger moray species encountered in the Indian Ocean. Its body is thick and muscular, covered in a mottled brown skin patterned with irregular white or yellowish spots. The most diagnostic feature — the vivid yellow coloration lining the inside of the mouth and gill area — becomes dramatically visible when the eel opens its jaws, a behaviour it performs regularly simply to breathe, pumping water over its gills. First-time divers often mistake this constant gaping for aggression, but it is entirely normal respiratory behaviour. However, like all morays, this species should be treated with caution and never provoked.

Behaviour and Diet

A largely nocturnal predator, the Yellowmouth Moray hides in reef crevices and coral overhangs throughout the daylight hours, emerging after dusk to hunt. Its diet consists primarily of fish, crustaceans, and cephalopods such as octopus. Morays possess two sets of jaws — the primary oral jaws for gripping prey and a second set of pharyngeal jaws located in the throat that lunge forward to pull prey deeper into the digestive tract. This extraordinary adaptation makes them highly efficient hunters on the reef.

Despite their fearsome reputation, Yellowmouth Morays are generally shy and non-aggressive toward divers who maintain a respectful distance. They are often observed partially extended from their crevice retreats, surveying the surrounding reef with keen, small eyes. On night dives in Mauritius, lucky divers may witness them actively hunting — a thrilling and memorable spectacle.

Habitat and Distribution in Mauritius

In Mauritius, the Yellowmouth Moray favours shallow to mid-depth coral reef environments, typically found between 5 and 45 metres depth. They are most commonly sighted wedged beneath coral heads, tucked into rocky outcrops, or sheltering within branching coral structures along the island's outer reef edges and lagoon walls. The species is widely distributed across the Indo-Pacific, ranging from the Red Sea and East Africa to the Hawaiian Islands, making Mauritius a prime location within its natural range.

Their status as a common species in Mauritian waters means that attentive divers have an excellent chance of encountering one on almost any reef dive, provided they scan ledges and crevices carefully. Dive guides familiar with local sites often know specific resident individuals that can be reliably found in the same hideout over many years.

Ecological Role

As apex predators within the reef ecosystem, moray eels like Gymnothorax nudivomer play a crucial role in maintaining the balance of reef fish and invertebrate populations. Their removal from an ecosystem can trigger cascading effects on reef biodiversity. Conservation of the reef habitats they depend upon — through responsible diving practices, reduced pollution, and marine protected areas — directly supports the long-term survival of this species in Mauritius.

Tips for Diving with Yellowmouth Morays in Mauritius

• Move slowly and calmly near reef walls and overhangs where they are likely to be hiding.
• Avoid placing hands or fingers into coral crevices — a moray bite, though rarely life-threatening, is painful and slow to heal.
• Night dives dramatically increase your chances of observing active hunting behaviour.
• Carry a torch to illuminate dark reef recesses where they retreat during daylight hours.
• Never offer food to morays — feeding wild eels is dangerous and disrupts natural behaviour.