Zebrafish Don't Get Jet Lag

Last week, i was pulling out my mask and flipper to go snorkeling in the turquoise waters of Antigua. The reefs were a few miles out, but i thought id just walk out from the beach, plunge under, and see what i could see. Unfortunately, the water was too volatile to see fish near the shore.
"Ya miss--the sand kicked up by de waves makes de water cloudy," said a friendly Antiguan guy from the resort dive shop. So, i wondered--if I can't see the fish, can the fish see me?
I remembered skimming an interesting PNAS paper about Zebrafish eyes before i left, so now that i've returned to the greater 48, i decided to peek at it again. Apparently, fish eyes work much like human eyes. The important difference between the two is that fish have eyes on the side of their 'face', giving them a limited space of binocular vision. Only in front of their 'nose' can they see in 3D. That means fish can see other sea life at different distances moving all around them but they can't judge how close they are to a shark, a menacing fisher's hook, or your toes until it is a few inches away and directly in front.
The paper describes the night vision of 5-day-old larval Zebrafish, which was a little more than I wanted to know, but is still kinda cool. At night, larval Zebrafish shut down their vision entirely (researchers found no electrocardiogram response in darkness.) It makes sense, since they can't see in the dark anyway. But, if you keep Zebrafish larvae away from light for two days, it turns out they still have a sense for day and night and turn their vision on and off accordingly. That means, Zebrafish larvae must keep to some sort of internal circadian rhythm, like humans.

Circadian rhythms help fish, humans, fungi, bacteria, and plants coordinate environmental changes with metabolic needs of the cell and body. Millions of years ago, early cells contained photosensitive proteins and circadian rhythms which may have protected replicating DNA from damaging UV radiation during the daytime.

If you've ever been jet lagged, you're personally acquainted with circadian rhythm. When I flew from LA to Antigua last week, I ended up in a location with very different light/dark cycle than home. Body no likey. Times for eating, sleeping, and other body chemical changes get off rhythm with each other and boy did i feel fatigued.


Doubtfully Zebrafish ever swim fast enough to make it from the Pacific to Atlantic ocean in 5 hours (especially since they are native to the southwestern Himalayan mountains), but they certainly use circadian rhythm at night to keep from exerting the energy it would take to maintain a vision system they don't need.

As for me, the 7.2 earthquake happened on the day I returned...as if i need anything else on top of jet lag to make me feel ill.



Farida Emran, Jason Rihel, Alan R. Adolph, John E. Dowling. Zebrafish Larvae Lose Vision at Night. Proceedings of the National Academy of Sciences. 2010