Today’s Factismal: The blob fish uses cartilage and fat in place of a swim bladder.
If you have ever made a Cartesian diver, then you have created the same system that most fish use to maintain their position in the water column. When you squeeze on the bottle holding a Cartesian diver, the pressure goes up, reducing the volume of air in the eyedropper which then increases its overall density, causing it to sink. Stop squeezing and the pressure goes down, allowing the air to expand which then reduces the eyedropper’s overall density, causing it to rise.
Inside most fish, there is a small, bladder-shaped organ that is filled with air and surrounded by muscle. When the fish wants to descend, it contacts the muscles around the bladder, compressing the air and increasing the fish’s density. When it wants to go up, it relaxes the muscles, allowing the air to expand and decreasing the fish’s density. By using a swim bladder, the fish is able to move vertically in the water without having to swim (which takes energy).
But swim bladders only work when it is easy to compress the air. As you go deeper in the water, the pressures increase to the point that it would be impossible to have muscles strong enough to squeeze the air any further. So what is a fish to do? If it is the aptly-named blob fish, then it uses cartilage and fat instead.
By growing just the right amount of fat, a blob fish can make itself float just above the bottom of the ocean. Like a small blimp filled with fat instead of helium, it drifts in the bottom currents and slowly moves over the crabs and other small crustaceans that make up its prey. When the blob fish comes upon an unwary crab, it suddenly sucks in the water like a Hoover from heck and pulls the crab into its waiting gullet. And when it dies, the blob fish slowly drifts to the bottom where its carcass is eaten by the crabs that it preys on, along with other parts of the ocean bottom community.
If you’d like to learn more about how animals live and form communities, then celebrate International Day for Biological Diversity with the rest of us today!