The ribbon eel, also known as the Bernis eel or Rhinomuraena quaesita, is a species of moray eel native to the Pacific and Indian oceans. Its slender body and broad dorsal fin give it the flat, ribbon-like appearance from which it gets its name, and an adult ribbon eel will grow to lengths of more than 3 feet (about 100 cm). Ribbon eels are perhaps most recognizable by their flared, fan-shaped nostrils.
In the wild, a ribbon eel can live for 20 years or more. Over the course of its life, the ribbon eel will change coloration and even gender. Until the eel reaches adulthood, it is black with a bright yellow dorsal fin. As the eel begins to mature, it becomes male, and the black body turns blue. When the eel’s body turns yellow with a black fin, it has reached its female stage.
Another unusual feature of the ribbon eel is the placement of its organs. The kidneys and most of the reproductive organs are behind the eel’s anus. No other vertebrate has organs located in this manner.
Ribbon eels appear to be quite aggressive and might even seem to be angry. Its mouth is constantly open, seemingly on the prowl and ready to strike. In fact, these eels keep their mouths open in order to breathe, not to hunt. In the wild, ribbon eels prefer to conceal themselves in rocks or under sand. To feed, they prefer to strike small fish that stray too close.
Aquarium owners and fish enthusiasts can purchase ribbon eels from pet shops, and their bright colors makes them an attractive addition, but they are notoriously difficult to keep. Even with a good supply of feeder fish, the ribbon eel usually will starve in captivity. Most often, the eel simply will refuse to eat and will die within a month or so. The ribbon eel generally is not recommended for captivity.
For those determined to make the attempt to keep a ribbon eel in captivity, there are some steps that can improve the eel’s chances. Providing concealment, three inches of sand at the bottom of the tank, a pile of rocks or even an artificial cave can help the eel feel more secure and make it more likely to eat. A good supply of feeder fish such as guppies or mollies will be needed, and a smaller tank will help to keep the food close to the eel. Other predatory fish should not be housed with the eel, because they are likely to go after the feeder fish before the eel is ready.