A male ribbon eel with the characteristic flared nostrils and barbel-like filaments on the lower jaw.
Color and Sex
This eel has several unique characteristics that have led some to suggest that they should placed in its own family, the Rhinomuraenidae. It has an extremely long, thin body, with broad dorsal and anal fins that give it a ribbon-like appearance. It has delicate jaws, fan-shaped nasal extensions, one barbel-like filament on the upper jaw and several on the lower jaw and its kidneys, and most of the reproductive organs are situated posterior to the anus. This last unique condition has not been reported in any other vertebrate. The ribbon eel can attain a maximum length of 47 inches.
You have know doubt seen both the blue and black ribbon eels and may know that these are actually the same species. You see, this eel is a protandric hermaphrodite; that is, all females are derived from males that have changed sex. As this sexual transformation occurs this eel also undergoes a chromatic metamorphosis. According to Fishelson (1990), as juveniles this species is jet black with a yellow dorsal fin. Between 23 and 32 inches it begins to transform into a male, at which time its coloration begins to change, from black to blue. The snout and lower jaw also turn bright yellow. This color phase was once thought to be a different species, having been refereed to scientifically as Rhinomuraena amboinensis. When an individual reaches about 33 inches it begins to develop female sex organs and changes colors until it is either yellowish-blue or entirely yellow. In the wild I have found that the blue color phase is most commonly encountered, the black color phase is occasionally observed and yellow individuals are rarely seen. One thing you should be aware of is that they can revert to a former color phase. For example, a blue individual we have in a customer's tank has changed back to the juvenile - black - color phase!
A juvenile and what appears to be a male transforming into a female (changing from blue to yellow).
Ribbon eels make striking display animals for the home aquarium; however, in some captive venues they may refuse to feed. There are several things you can do to help initiate feeding in a ribbon eel. First of all, you need to provide adequate hiding places so that your eel "feels" secure. One way to do this is to place about 3 inches of live sand and an 1 inches of coral rubble on the aquarium bottom and a mound of live rock on one side of the tank or against the back glass. By setting-up your tank in this manner you will provide sand and coral rubble for the eel to burrow under or a coral head of live rock for it to hide within. I have also seen ribbon eels adopt artificial caves as refuges. You can create a cave by gluing crushed coral and chunks of rubble to a fish bowl, which can then be lain on its side on the aquarium bottom. A long piece of PVC pipe, that is no more than twice the diameter of the eel, may also serve as a sanctuary for these animals. Place a 45 degree elbow on one end of the pipe and cap the other and bury it under the substrate.
A full-fledged female ribbon eel sporting her canary yellow garb!
Feeding Ribbon Eels
Live feeder fish are also necessary to entice a ribbon eel to feed. You should add a dozen or more mollies or guppies to your tank. In order to increase the concentration of potential prey in the vicinity of an eel, it is best to house it in a smaller tank (e.g., 30 gallon) or partition off the eel's preferred hiding place if it is being kept in a larger aquarium. It is also easier to feed a ribbon eel if it is not housed with voracious carnivores that will snap-up the feeder fish before the eel is enticed to feed. In fact I would recommend you keep your ribbon eel in a tank on its own or with a conspecific. Some ribbon eels can be trained to take small pieces of fish impaled on the sharpened end of a piece of rigid airline tubing or to take food off the aquarium bottom. When using a feeding stick it is important that you present the food in a non-threatening manner (i.e., do not shove the food in the eel’s face). Instead, you should move the food around the tank as if it were natural prey.
A female ribbon eel in the characteristic posture. This is the same moray in the second photo above.
Several months ago, our technicians in Kansas City placed two ribbon eels in a customer's reef aquarium - one was black, the other was blue. The black ribbon eel immediately took pieces of fresh shrimp. The blue individual refused to feed. After several weeks in the tank, our technicians noticed that some of the fish in the tank were starting to disappear. This included a fairy wrasse and a neon dottyback. They found out where these other fish went when they added several red-striped anthias only to have one snarfed-up by the blue individual! Subsequently, the blue ribbon even ate a Banggai cardinalfish that appeared as though it was to big to ingest. Since then, the eel has begun eating larger livebearers (six to eight mollies per week). The larger blue individual (as mentioned above) has also changed from blue back to the black color phase (which is a bummer!).
Be aware that ribbon eels are especially proficient at finding small cracks and holes in the aquarium back stripping to exit through. They will also swim up siphon tubes that lack strainer caps.
© Scott W. Michael/ Reef Tectonics