“…and today we’re talking about an ice cold krill killer. But more on that later.”
The trend of swimming in cold water for health benefits is doggy paddling its way into the public zeitgeist. But what if you absolutely had to live in freezing waters in order to survive? The crocodile icefish lives up to its name by living down in the depths of the Antarctic Southern Ocean. But how does a cold blooded fish not turn into a popsicle at such extreme temperatures? Well, it’s all in their blood and sometimes you just need a lot of it to survive here in Life, Death, and Taxonomy.
Description of the Crocodile Icefish
The family members that are all called crocodile icefish come in several shapes in sizes, but they generally have:
- A long torpedo shaped body
- Fins that run the length of their back and the back half of their underbelly
- Long snout with large crocodile style mouth
- Large eyes.
- They can also be striped for pattern disruption.
Measure Up
Welcome to the beloved Measure Up segment. The official listener’s favorite part of the show! The part of the show when we present the animal’s size and dimension in relatable terms through a quiz that’s fun for the whole family. It’s also the part of the show that’s introduced by you when you send in audio of yourself saying, singing, or chittering the words Measure Up into ldtaxonomy at gmail dot com. We don’t have a new Measure Up intro.
Length
- 35 cm (14 in)
- How many Crocodile Icefish go into the outer ring of fortifications in Verdun?
- Hint: The forts in Verdun had begun to be modernized with sand buffering and steel-reinforced concrete in 1880. In the Battle of Verdun, the ring of fortifications had 79 guns in shellproof turrets and more than 200 light guns.
- 126,720 fish. The outer ring of the Fortified Region of Verdun was 28 mi (45 km).
Depths
- 50–250 m (160–820 ft)
- How many depths of the M1 helmet go into the living depth of the crocodile icefish?
- Hint: The M1 helmet was the standard issue American helmet for ground troops in WWII all the way to its retirement in 1985. The need for helmets was first realized in WWI, when bonk injuries increased rapidly because of shrapnel and debris flying into trenches during bombardment. The U.S. first developed the M1917, but it was poorly balanced and lacked protection from bullets coming at you in the normal lateral direction. Before the U.S. entered WWII, they decided to get their helmets in order. Brigadier General Courtney Hodges oversaw the development of a new helmet without a brim, more neck protection, and a visor. They also added a suspension system in the style of football helmets at the time. During testing, the helmet resisted a point-blank shot from a .45 pistol.
- 1,405 helmets. The M1 has a depth of 7 inches (180 mm)
Fast Facts about the Crocodile Icefish
The crocodile fish live in the Arctic and Southern oceans. Only our friend the pike icefish is found north of the Antarctic Polar Frontal Zone in the bottom half of the world.
There are 16 species of crocodile icefish. They are what’s called a demersal species, which means they like to hang out on the ocean floor.
Icefish eat mostly fish but they can also feed on krill. They hunt as ambush predators, remaining still and attacking suddenly. This feeding style makes them less active than stalkers, which means they can survive with long periods between munches. When they do eat, they consume fish up to half of their body length.
Major Fact: Cold As Ice
One thing we know about cold blooded animals is that temperature matters.
But the crocodile icefish is found as deep as 820 ft around the waters of the Southern Ocean around Antarctica. As low as 28°F in some areas.
Sounds like a recipe for Mrs. Paul’s crispy battered frozen fish sticks, not a thriving population of still alive fish
So how does a fish survive in the depths of the antarctic?
The answer is: it actually has to live in near-freezing water. It bleeds white like a Weyland-Yutani android.
The blood of all icefish is colorless because it doesn’t have any hemoglobin, which is the protein in your blood that binds to oxygen, allowing it to get oxygen from the lungs and transport it throughout the body.
So red blood cells are usually absent. Even if they’re there, they’re useless. Icefish have remnants of the gene that makes hemoglobin, but it’s not intact.
So how does the icefish get oxygen to all its important bits?
Without these tools, icefish have low metabolic rates and can only carry 10% of the oxygen that related fish can with their fancy shmancy hemoglobin
They still have gills, but oxygen is absorbed straight from the water into their plasma. This is easier done in colder water since gas is more soluble in colder water than it is in warmer water. This is why arctic and antarctic waters are so oxygen-rich
Icefish also have larger blood vessels, larger hearts, and also 4 times as much blood as other fish
They also don’t have scales, which researchers thought allowed them to absorb oxygen directly through their skin
While they can absorb oxygen through their skin, they get most of their oxygen from their gills
So they still get their oxygen by taking water into their gills and absorbing the oxygen, but it goes directly into the bloodstream and into the muscles and heart without the efficiency of hemoglobin that the rest of chordata tends to enjoy.
Researchers theorize that, since you need iron for hemoglobin production and iron can be hard to come by in the open ocean, the icefish adapted to go without it.
Ending: So take an ice bath, dive down to the depths of the southern ocean and like Foreigner be as cold as ice like the icefish here in LDT.