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Fish have 3 second memories, WRONG, fish feel no pain, WRONG, fish are all cold blooded, Correct .....Uhm, no, not anymore. Scientists have recently discovered that the Moonfish (also known as an Opah) contradicts our assumption that all fish are cold blooded.

We love it when things that we have long assumed as fact are actually found to be very wrong and the text books need to be re-written. In this case, the old assumption that all fish are cold blooded has recently been proven incorrect when researchers found that the car-tire-size Opah Fish (Lampris guttatus) has actually got warm blood.

Most fish are exotherms, meaning they require heat from the environment to maintain their body temperatures (much like snakes and lizards). The Opah however is an endotherm (much like birds and humans) because it keeps its own temperature elevated even when it dives to chilly depths of over nearly 400m where it occurs in temperate oceans around the world.

Study leader, Nicholas Wegner, a biologist at the National Oceanic and Atmospheric Administration (NOAA) Fisheries explains that the Opah Fish keeps warm by constantly flapping its pectoral fins which are used in continuous swimming. The fish has blood vessels in its gills that carry warm blood from the body's core. These vessels wrap around other vessels near the gills, where the fish breathes, bringing in oxygenated, cold blood. The result is a self-made heating system (which works a bit like a car's radiator) that keeps the fish's brain sharp and its muscles active so it can swim fast and grab prey regardless of how cold the water is.

This is a great advantage in deep cold water, where other predatory fish, such as tuna, can only spend short periods of time before they need to come to the surface to warm up. The warm blood ensures a sharp reflex system and  keeps it's muscles active, all resulting in a very efficient deep water predator with a sneaky advantage. Researchers discovered this nifty adaptation by attaching heat sensors to the fish and found that no matter how deep they dive, their body temperatures stayed about 5 degrees Celsius warmer than the surrounding water. Fat deposits around the gills and muscles also help to further insulate the fish.

How many other warm blooded fish are out there or have nifty adaptations we couldn't begin to imagine? What does this mean for our "moral standpoint" that it is OK to treat fish "cruelly" simply because they are cold blooded? The moral of the story.....we still have a lot to learn, so be nice to fish! 



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