My second favourite fish

By Siouxsie Wiles 28/01/2011

Whenever I visit somewhere new I go on the hunt for an aquarium. I’ve just been in Vancouver and found an hour to explore it’s aquarium before I had to race off and navigate the maze that is US Customs and Border Control. Now, I have my own system for ranking aquariums and its very simple: the presence or absence of bioluminescent fish. I can tell you that I have been to a lot of aquariums all over the world and there aren’t many that have bioluminescent fish. But Vancouver does. Needless to say I spent most of the hour stood watching them. So allow me to introduce my second favourite fish*, the Splitfin flashlight fish.

Splitfin flashlight fish (Kenneth Lucas/California Academy of Sciences)
Splitfin flashlight fish (Kenneth Lucas/California Academy of Sciences)

The Splitfin flashlight fish (Anomalops katoptron) lives in the warm waters of the Pacific and is named for the bean-shaped bioluminescent organ (photophore) below each eye. These fish are nocturnal, emerging at night to feed on zooplankton and smaller fishes. Flashlight fish use their light to attract prey as well as communicate with each other. They can also use it for a nifty predator evasion strategy (blink and run) where they rapidly flash their lights while swimming in one direction and then switch off the light and swim off in a different direction. The light is produced by bioluminescent bacteria** which don’t appear to be culturable outside of the fish. Prof Margo Haygood has done a lot of work on trying to identify the elusive little buggers using molecular typing techniques.

It was great watching the flashlight fish in Vancouver. There were a couple of fish that seemed to be hanging about with their lights on in a ‘look at me’ kind of way. Then there were others who were swimming around flashing as they passed each other (saying hello, maybe?). What always strikes me when I see bioluminescence in its natural habitat is how much brighter it is than anything we can make. I’m especially impressed by the amount of light that shines from the rear end of the glow worms (Arachnocampa luminosa) at Waitomo. I’ve been engineering bacteria to go glow for years now. Its fairly easy***, just a case of putting the five lux genes into the bacteria of interest. We mess around with all sorts of things to make them brighter (promoters, ribosome-binding sites, codon usage) but still can’t get anything like nature can manage. Amazing.

*My favourite is the anglerfish, just in case you were wondering. More on that another day.

**More on this another day too.

***Slight exaggeration…. it can be fairly easy. It all depends on the bacteria we want to engineer. Sometimes it can be a bloody nightmare. Like my current project.

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