The Covert World of Fish Biofluorescence
My research on biofluorescence started accidentally.
At the beginning of 2011, I went down to Little Caymen Island to help some colleagues photograph
coral biofluorescence. And just by accident, a green fluorescent
eel happened to swim in front of one of our photographer’s cameras.
We didn’t actually see that underwater. It was only afterwards, in the image the photographer
presented to us. We thought at first it was a joke, that it
was photoshopped in, but he confirmed that it wasn’t. And we could tell that
it was a false moray eel And it was brightly green. There was nothing reported in the literature
about green fluorescence in fishes, so it got us thinking about how widespread this
phenomenon might be in fishes, and then led to other studies where we went down, collected
as many fishes as we could, and scanned them for biofluorescence. We felt like we were really on to something new here, like we were just starting to discover all these different families. There’d been one paper that mentioned a little
bit of red fluorescence, but now we were seeing green, we were seeing patterns, we were seeing
both green and red. And the fact that we were seeing it in so many different species really
got us excited. Biofluorescence is an optical property in
which light is absorbed and then given back off as a slightly lower energy.
So blue light might be absorbed, taken in, and given back off almost instantaneously
as green or reds. Biofluorescence was first discovered in the 1960s.
The scientists found that it was tightly coupled with a bioluminescent jellyfish, where the
jellyfish is producing a blue light, and there was this green fluorescent protein that was
absorbing that blue light and giving off the green light that you would see from the animal.
As the molecular biology revolution took hold in the 1990s, they were able to figure out
the sequence of that fluorescent protein. They could take that out, put it in front
of another gene. In a living organism, it’s like putting a
bicycle reflector on it. And suddenly now you could look at gene expression,
you could see how proteins move around inside cells. So this really has transformed our way in which we can study life. It probably took us over two years of designing different kinds of equipment that we can use
to study fish biofluorescence. For the submarine, we also designed different
kinds of cameras that could go to 4,000 meters deep. We used very high-energy blue lights to stimulate biofluorescence. And then we have a filter over the camera that takes out this blue energizing light
and lets us see the lower-energy, longer wavelengths, the greens, red, oranges and yellows. Many of the fish groups in which biofluroescence is very common have a filter built into their eye that enables them to see biofluorescence. It functions to eliminate any reflected ambient
or blue light, the same kind of setup we use in our cameras. In our search to find out how many species and how prevalent biofluorescence is,we took trips to the Bahamas, we took trips to the Solomon Islands. We went to the Mystic Aquarium, and we kind of went tank by tank by tank, seeing which fish displayed biofluorescence. What I found most surprising is just how widespread
it is across the tree of life for bony fishes and cartilaginous fishes, as well.
What I also find interesting is that it’s most varied and most common in very cryptically
patterned camouflaged lineages on the reef. Fishes that you would never notice otherwise
under white light, under fluorescent light they’re extremely brilliant and vivid. We know that biofluorescence probably functionsin probably mating behavior, communication within a species. So species are somehow identifying each other
potentially using fluorescent patterns, which is quite novel.
We have to put ourselves in the position of the fish and what they can see.
And some of these patterns may actually act to make the fish very difficult to see
for other fish.