'Lazy' Sunfish is Actually an Active Killer

If you've ever seen a massive sunfish in the ocean, it's hard not to think of these animals as lazy. That because the strangely shaped animals tend to just drift around in surface currents while they soak up the Sun - a behavior that earned them their common namesake. Now however, new research has found that while these 'lazy' fish aren't darting around, they are diving deep to ravage unsuspecting prey.

That's at least according to a study recently published in the Journal of Animal Ecology, which details how sunfish (Mola mola) are surprisingly aggressive and even wasteful predators when they leave their sunny waters for deep-ocean dives.

To determine this, a team of experts attached accelerometers to several wild sunfish found near Funakoshi Bay, off the east coast of Japan, and monitored when and where they swam. They found that while they spend about 40 percent of daylight hours within the top five meters of ocean basking in the Sun's rays, they spend the rest of their time diving to depths of about 200 meters. The tracking devices even revealed that these slow and massive fish, weighing up to about 1000 kilograms (~2200 lbs) can reach depths of a whopping 800 meters (~0.5 mi). (Scroll to read on...)

But what are they doing so deep? The team attached several advanced monitors, including a video camera to more wild sunfish and discovered that theanimals were hunting jellyfish and other jelly-like invertebrates (mostly siphonophores). Interestingly, the Mola mola weren't even eating all of their prey, choosing instead to tear the jellies to bits before devouring their gonads and oral arms in particular - parts significantly more nutritious, compared to the iconic bell of your run-of-the-mill jellyfish.

So if sunfish are actually such violent and active predators, why do they laze around so much near the surface? The researchers also determined that the sunfish lost a great deal of body heat every time they dived to colder depths. Those hours of lazing in the Sun's rays, the researchers concluded, are then very necessary for the fish to warm up enough to avoid freezing during their next dive.

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