IF YOU’VE EVER OBSERVED A SEAHORSE, its tail wrapped around a sea rod or some other feature, its demeanor would seem to suggest lethergy and a wish that you would just go away. THERE’S CUNNING IN THAT CURVE In reality, odd-shaped fishes as seahorses are, their curved bodies and horse-shaped head-and-neck anatomy give them an edge over their straight-shaped pipefish cousins by increasing the speed and distance with which they can capture prey (mostly
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ABOUT 40 PERCENT OF BONY FISHES live in freshwater but only five percent of sharks, rays and skates can do so. There a number of reasons cartilaginous fishes don’t do well in freshwater, including problems with dehydration and reproduction. SINK OR SWIM. MOSTLY SINK A team of American and Australian scientists have determined that another reason is an inability to maintain buoyancy control in freshwater. In short, in freshwater, sharks and their kin would tend to sink like newbie divers. NEEDED: LARGER
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UNLIKE BONY FISHES, SHARKS maintain buoyancy with oil-filled livers rather than bony fishes’ air bladders. Recently, it was revealed that doesn’t work well for them in freshwater, where they tend to have poor buoyancy (see “In Freshwater, Sharks Can’t Control Buoyancy“). DEEP-WATER SHARKS CAN Now a study has found that deepwater sharks, such as the bluntnose six gill shark, have better than average buoyancy at the depths they frequent. Science writer Chris Cesare describes the study in an AAAS ScienceShot
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“THEN THE OCEAN FLOOR SUDDENLY FELL AWAY. We were hovering like unharnessed window washers on a vast wall of rock and coral, the outermost edge of the second-longest barrier reef in the world, the boundary of the big deep.”We were looking for a pod of dolphins that had graced these parts the day before. But I wasn’t prepared for infinity.” — New York Times science writer Dennis Overbye GOOD BUOYANCY IS IMPORTANT IN DIVING –
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