Mola mola – the Sun(fish) of the Sea

The ocean sunfish is the largest bony fish in the ocean. Its Latin name, Mola mola, means “millstone” (technically, it means “Millstone millstone”), and derives from the fish’s grey color and round, flat shape. 

16D26 Ocean Sunfish

Ocean sunfish are rare in captivity, largely because they eat only jellyfish–a difficult diet to provide, because the low nutritional value of jellyfish means the ocean sunfish needs to consume enormous quantities of live prey to stay alive. Also, ocean sunfish are poor swimmers, which makes them difficult to house.


Ideally, ocean sunfish require a kreisel tank — a cylindrical aquarium with no corners for weak-swimming fish to get stuck in. (If you’ve ever seen jellyfish in an aquarium, you’ve probably seen a kreisel tank. Ironically, this predator and its prey are both victim to similar kinds of trouble with strong or lateral currents.)

The photos on this blog are of the captive ocean sunfish at Tokyo’s Sunshine Aquarium–one of the most popular exhibits there. The sunfish lives alone, but in the wild these fish spend most of their lives in isolation, so it doesn’t seem to mind.

16D26 Ocean Sunfish 2


Like many marine fish, sunfish are curious creatures and well aware of the world beyond the walls of their aquarium tanks. This one actually followed my son along the glass–three times–while we were visiting. He tried to move to let other people have a chance to stand in front of the fish, but the fish wasn’t having it. My son finally stopped moving because the poor thing had to work so hard to follow him along the glass, and it wasn’t letting other people see it anyway. (Aquatic creatures have an odd, and noticeable, attraction to my son — and have, since he was a toddler.) As soon as he stood still, the fish stopped moving, and a crowd gathered.

16D26 following C

You can see my son’s shadow on the left side of the image above, and it’s clear that the fish is following him. (We tested this thoroughly..and he was the only one it followed like this while we were there.)

Children often like sunfish because, despite their enormous size (adults can weigh up to 2,200 pounds and measure over 8 feet from fin tip to fin tip) their goofy faces and large round eyes make them highly approachable creatures.

16D26 sunfish closeup

Ocean sunfish belong to the same biological order as pufferfish and filefish, and share the same mouth structure as those fish, with four fused teeth that mimic a beak. The sunfish’s teeth are harder to see, because they’re set farther back in the mouth–a mouth which almost never closes completely, giving the fish a somewhat odd appearance.

16D26 sunfish mouth

And by “odd,” I mean it’s pretty freakish–and yet, I find them completely adorable. Curiously, I’m not alone in that assessment. The gift shop at Sunshine City Aquarium offers a variety of ocean sunfish-themed merchandise, including stuffed animals (one of which sits on my bed as I write this post)

So…what do you think of the ocean sunfish? Freakish monster or sweet behemoth?