Crocodile Icefish
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Basic Information

The Crocodile Icefish are a number of related species of ambush predator fish found in the extremely cold waters around Antarctica. They are classified as Family Channichthyidae.

One of the most interesting things about them biologically is that they have transparent blood. It's not red, because it completely lacks hemoglobin. This is a mutation that would have proven fatal in nearly any other environment on earth, as hemoglobin is what our blood uses to efficiently transport oxygen throughout the body. Nearly all vertebrates have red blood for that reason. However, in water that is very cold, not having hemoglobin is not nearly as much of a disadvantage: gases are more soluble at cold temperature, so they are able to stay oxygenated without it. The blood is thinner without hemoglobin, which could be helpful in the cold. They also have very low metabolisms, as you might expect of a cold-blooded ambush predator in such cold waters, and that helps too. Instead of having efficient blood, they just have more blood volume than normal for a fish of their size, and it does the trick.

Thanks to their low metabolisms, they can go long stretches of time between feedings.

The largest Crocodile Icefish on record was about 50 cm (about 20 inches).


Game and Story Use

  • Could be used as a model for a monster that lives in a super-frigid arctic-style environment.
    • Ambush predator, possibly with camouflage to hide it as it sits unmoving for hours waiting for prey to wander near.
    • The clear blood may make it harder to estimate how badly injured it is, and the lack of hemoglobin may alter the scent in the water if it is wounded so that sharks and the like have a harder time identifying it. The high blood quantity might either help or hinder its natural healing and recovery rate, and the GM could probably claim either and make it sound justified scientifically.
    • The high blood volume could be exhibited as high blood pressure. If you stab or cut a monster of this sort, a clear fluid sprays out. If it has some sort of blood-borne illness or poison blood, that's going to really up the danger of melee combat. So that could be fun.
  • Can also be transposed to environments colder than Earth: See Ice Planet, Ice Giant (Planet), etc. This lets you still use life as we know it, without having to resort to Hypothetical Types Of Biochemistry to create a believable ice-alien.
    • A breed of Crocodile Icefish (genetic engineering optional) might be intentionally brought to such a world to help seed the slushy oceans and take a role in terraforming.
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