The ocean sunfish (Mola mola) has a radiant name, but its appearance doesn't exactly match its glowing moniker. Wrinkled and colored a sickly shade of gray, the sunfish doesn't exactly shimmer. However, its pallor isn't nearly as distracting as its awkward shape -- the fish is usually taller than it is long. Moreover, the sunfish's mouth is constantly agape, granting it a dumbfounded look of everlasting surprise. With that gaping maw, the sunfish primarily consumes jellies, a less-than-sumptuous prey. Yet it is on this slimy diet that sunfish can attain weights of over 1,000 kilograms and lengths of nearly six feet. The largest sunfish weighed in at 2,300 kilograms and extended over ten feet in length! Not bad for a fish that, as a baby, begins life measuring just four millimeters across.

The ocean sunfish's immense size has earned it the title of "world's largest bony fish." As you might imagine, getting that bulky takes some serious growing. Researchers recorded a captive sunfish ballooning 880 pounds in fifteen months, an average of 1.8 pounds per day. That's far, far above other ray-finned fish, even ones that are similar in size to the sunfish.

Recently, researchers published the first genome sequence of the ocean sunfish. The results rendered insights into the fish's incredible growth rate.

"Several sunfish genes involved in the growth hormone and insulin-like growth factor 1 axis signalling pathway were found to be under positive selection or accelerated evolution, which might explain its fast growth rate and large body size," the researchers noted.

Indeed insulin-like growth factor 1 (IGF-1) is one of the primary growth hormones in humans, as well. People insensitive to or deficient in the hormone experience stunted growth or dwarfism. The ocean sunfish, on the other hand, seems to produce a boatload of the stuff. This means that with plenty of food, the charismatic fish can grow and grow and grow.

Source: Hailin Pan et. al. "The genome of the largest bony fish, ocean sunfish (Mola mola), provides insights into its fast growth rate." GigaScience 9 Sept 2016 5:36 DOI: 10.1186/s13742-016-0144-3

(Images: Per-Ola Norman , G. David Johnson)