An Australian marine photographer captured a rare sighting of a fish propelling itself forward from inside a transparent jellyfish.I came across this fish (presumably a juvenile trevally) while snorkeling along Double Reef on Guam in 2013. The fish swam in and out of the crown of the jellyfish multiple times over the course of several minutes.
image credit: timsamuelphotography
The fish was able to steer the jellyfish as it swam inside, often turning away from me as I followed. It has been postulated that the fish is using the jellyfish as a shield to protect itself as it swims in open waters.
image/video credit: Brent Collins
Jellyfish experts were unable to identify the jellyfish with certainty, but a likely candidate is a box jellyfish. Box jellyfish use venom to prey on fish.
“They evolve to kill prey instantly,” Luciano Chiaverano, a post-doctoral researcher at the University of Southern Mississippi, told CBC. “This might be a case where the prey is too big to kill it right away, so the fish might have some time to swim around inside.”
The fish does appear to be in the jellyfish’s stomach. However, box jellyfish would normally eat prey a third or quarter the size of their bell, making this fish an unusually large target for a box jellyfish.