[Coral-List] Strobes blind seahorses? (Scott M. Taylor)

Dr. Scott Taylor staylor at smu.ky
Wed Apr 7 12:22:34 EDT 2010

I would just like to add a bit to the discussion regarding strobes blinding
seahorses, because I have done some research on the fish visual system. As
some have said, the only potential issue here is TEMPORARILY blinding the
animals that might make them more susceptible to predation. Bright light
bleaches the photoreceptors (renders the photopigments nonfunctional for a
short period of time), and it can take minutes for complete recovery. To my
knowledge, there are no data regarding strobe lights making small fishes
more susceptible to predation, but it seems plausible and might make an
interesting study. I would not expect this to affect seahorses any more than
other small fish species. I also would not expect a profound effect unless
you are photographing animals at night or in deep, dimly-lit water. Rod
photoreceptors are used for vision in low-light conditions, and they are
bleached very easily by bright light, and thus in the dark vision will be
impaired more profoundly by a bright flash. Cone cells are used during the
day and are less affected by bright light. You can demonstrate this to
yourself by sitting in the dark for a few minutes (relying on your rods for
vision) and then flashing your eyes with a camera strobe. It will take a bit
of time for your eyes to completely recover. 


A strobe is not going to cause permanent blindness in a fish- it would
likely take long-term exposure to high levels of radiation for damage to
occur. And even if damage did occur, the fish retina has the amazing ability
to regenerate. New cells are continuously produced in the retina, and
therefore it can actually heal if there is damage- UNLIKE the mammalian
retina that does not regenerate. 


So, for all of these reasons, temporary blindness is very likely to be
caused by a strobe, especially in dark water. This might render fishes (not
just seahorses) more susceptible to predation for a few minutes or so. If
they are not killed by a predator, they will recover quickly and completely.
If others would like to report instances of small fishes being consumed by
predators immediately after being photographed with a strobe, we can start
putting together some evidence that there might be some truth to this
"myth". I am interested and would be happy to compile such data. You can
send it to me directly at staylor at smu.ky. 



Scott M. Taylor, Ph.D.

SMU School of Veterinary Medicine

Grand Cayman, B.W.I.



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