Episode 204 – Ribbon Eel: The Future is Female

“…and today we’re talking about the Christmas decoration of the sea. More on that later.” 

The ocean can be a dangerous place. There’s always a bigger fish waiting for an unsuspecting creature to become its next meal. One brightly colored eel avoids these threatening open maws by rarely leaving their homes in the crevasse of protecting coral. But when they do they showcase a mesmerizing ribbon-like display of yellow and blue. Sometimes, even content introverts have to make their way out into the world in Life, Death, and Taxonomy.


  • Ribbon eels are long, thin, and very colorful
  • Adult males have bright blue bodies with a large yellow dorsal fin jutting out like a sail or keel across their entire body
  • They have thin blue moray eel faces
    • Their noses, eyes, and jaws are bright yellow
    • Their nostrils are actually extended and flare out from their faces. They look like thin yellow beetle wings sticking out of their noses.
  • Adolescents are black with yellow accents – they turn blue as they age
  • Females are completely yellow

Measure Up 

Welcome to the beloved Measure Up segment. The official listener’s favorite part of the show! The part of the show when we present the animal’s size and dimension in relatable terms through a quiz that’s fun for the whole family. It’s also the part of the show that’s introduced by you when you send in audio of yourself saying, singing, or chittering the words Measure Up into ldtaxonomy at gmail dot com.

We do have a new measure up intro this week from Nora!

Female Length

  • 130 cm (51 in)
  • How many female ribbon eels go into the tallest library in the world?
  • Hint: The record is held by the National Library Of Indonesia in Jakarta. The building was built in 1980 and is now home to 4 million items (not just books).
  • 97 eels. The building is 126.63 m (415 ft) with 27 floors.

Male Length

  • 65 to 94 cm (26 to 37 in)
  • How many male eels go into the world’s tallest cake?
  • Hint: Another record for Indonesia. The cake was made in Jakarta by the Hakasima-Nilasari Culinary School. It was made for a Christmas celebration.
  • 35 eels. The cake was 33 m (108.27 ft) tall. 

Fast Facts

  • Range: All across the Indian ocean and into the Pacific including French Polynesia and Australia
    • They hang out in coral reefs
  • Diet: small fish like guppies, minnows, and crustaceans
  • Behavior: 
    • Live for 20 years in the wild but only for a month in captivity

Major Fact: The Future is Female

Ribbon eels never have gender reveal parties, and not just because they are essentially a second baby shower. Actually, all ribbon eels are born male. 

As we learned with the mourning gecko, it’s possible to have a single-sex species. But they are usually all female. All-male species don’t really work out, because you need an egg to grow a new eel.

So ribbon eels are born male but they don’t stay that way. Ribbon eels go through several life stages that are all color coordinated like a Star Fleet ship. 

Juveniles are all black with yellow on their dorsal fin, nose, and cheeks. As they age, the black is replaced by a brilliant blue. When they reach a certain age, they start to lose their blue and turn all yellow. This represents the intersex stage, when they are changing from male to female. 

This is something called protandry. It’s a type of sequential hermaphroditism, which is when a plant or animal changes sex at some point in their life. 

Clownfish are similar. Males are born and the largest among them becomes a female. But ribbon eels don’t become female when certain criteria are met. So far as we know, the change from male to female is a typical part of their life cycle.

Protandry is less common than protogyny, which is changing from female to male. Protogynous species may have a some for of sexual selection where the female’s prefer males that are larger or able to win physical matchups. 

Perhaps it’s better for the Ribbon eel to be female when it’s larger to defend eggs?

What’s weird is that everything is thrown out the window in captivity. They rarely survive more than two years in captivity. They often stop eating after they are captured. Color changes also seem to happen regardless of their sex. 

Ending: So share an underwater den with someone, be colorful, and stay out of captivity if you want to live a long life.