What the Fish? Episode 3: You Light Up My Life

How does a fish make light?

Bioluminescence, the production and emission of light from a living creature, is widespread among different groups of marine fishes (e.g., anglerfishes, flashlight fishes, dragonfishes). Most organisms produce light through a chemical reaction between luciferin (a small molecule) and oxygen. The enzyme luciferase speeds up this reaction, resulting in the production of light. But unlike the incandescent lightbulbs in your home, this light gives off almost no heat. Some fish species have the ability to produce the chemical compounds necessary for bioluminescence themselves (such as lanternfishes), while others rely on symbiotic bacteria to create and generate light (including the beloved anglerfish in our logo).

Why would a fish want to make light?

The majority of bioluminescent fishes are found in the deep sea. Below 1,000 meters there is no visible sunlight in the ocean. As a result, many organisms that live below this depth have evolved bioluminescent structures, and fishes use this light in a variety of ways. Some fishes use light for camouflage, specifically counterillumination.  This is where the fish emits light around its belly to match any light coming from overhead, making it invisible to predators looking upwards for shadows in the water column. Others use light to attract and catch prey, such as the beckoning luminescent lure of the anglerfish. Fishes will even use light for communication in order to recognize each other in the darkness of the deep or to communicate with potential breeding partners.

Fish of the Week: Ponyfishes (Family: Leiognathidae)

Family: Leiognathidae

Distribution: Indo-Pacific

Maximum Size: 21 cm

Fun Fact: Some ponyfishes can emit light through their foreheads!

Encyclopedia of Life: Ponyfishes

Ponyfishes include more than 60 species of small silvery fishes found throughout the Indian and West Pacific Oceans. While seemingly inconspicuous at first, ponyfishes have one of the most fascinating bioluminescent systems currently known to science. All ponyfishes have a specialized doughnut-shaped pouch, that branches off from and surrounds their esophagus that stores bioluminescent bacteria. During their mating season, ponyfishes open a series of shutters and windows on their bodies to allow for the transmission of the continually glowing bacterial light. This results in brilliant displays of flashing luminescent patterns. While most bioluminescent fish species live in the deep sea, ponyfishes actually inhabit nearshore habitats where they use bioluminescence primarily for communication.


You can follow us on Twitter and tweet us your fishy questions @FM_WhatTheFish or email us at whatthefish@fieldmuseum.org.

So long, and thanks for all the fish!

Fish Nerds Podcast Team:

Beth Sanzenbacher

Eric Ahlgren

Leo Smith

Matthew P. Davis

Focus: Amphibians & Reptiles
DNA Discovery Center