Called freshwater killer whales, huge catfish have learned to catch and eat birds. In southwestern France, pigeons bathing on beaches are in for a nasty surprise. Big catfish lurking just offshore, waiting for a bird to go just a bit too far into the water. Big schools of fish make better decisions than small schools of fish. Less smoking, less risky sex, and no flirting with predators.
How can this be? Is it more likely that big schools have some super-smart fish that help the group? Or is it just that numbers are helpful? If you've ever watched the behavior of fish schools being chased, you'll probably guess the answer, it's group behavior that helps individual fish survive.
Watch these videos (below) and other you can find online for "super-organism" behavior where fish schools look like one giant creature swooping and swirling.
If I remember right, the great oceanographer John McIsaac once theorized from physical principles that a fish school could function like a lens focusing sound so that the fish could detect predators better in a swarm.
hat tip: Deep Blue Home
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Thanks to The Echinoblog for this revelation of the brittle star of death from the Phillipines, Ophiarachna incrassata, described as a "crepuscular and nocturnal predator "...At night (this behavior was only observed using red lights), this species will sit up on its armtips and form a "pseudocrevice" , maintaining the position (shown in the top diagram) for many minutes without moving. Apparently, he found many individuals found in this posture during the night.Oh my! Tweet
From here, it gets interesting.
Short version: Fish get too close..and then...
Ophiarchna will RAPIDLY wrap its body into aspiral (as above) ..forming the "body spiral". This action apparently takes less than a SECOND.
The fish is trapped by the elongate spines on the arms creating "bars" to a "prison" formed by the helically arranged arms.
The brittle star holds the position for several minutes, gradually lowering the disk toward the bottom and moves its arms outward.
Prey captured was digested head first as it was swallowed WHOLE by the ophiuroid.
Interestingly, Ophiarachna takes advantage of several of these fish's natural nocturnal behavior to find hiding spaces. And although they feed on a variety of items (e.g., algae, etc.) this behavior was observed to be quite successful.
