Arctic conditions can be brutal for all of us. Just take the recent effects of the Polar vortex that ravished the better part the continental United States. On land, we are able to stay active or simply get out of the brutal conditions, this isn’t the case for many of the marine fish living the majority of their lives in sub-freezing conditions. So how do they keep their fragile fish bodies from freezing like a deer in headlights?
Well, it depends on how you define “freezing” and what you think is ultimately sending a fish to that “big ocean in the sky” (at these low temperatures). We all know that pure water freezes at 32°F (0°C). One other thing to keep in mind is atmospheric pressure, and pure water only freezes at 32°F (0°C) at 1atm. With increased pressure (2, 3, 4+ atm) the freezing point of pure water begins to decrease ever so slightly.
OK, so that takes care of the “freezing” part.
So, what actually turns a fish into natures Weekend at Burnie’s? It’s two main things.
Environmental cues tell the cold water fish that winter is coming.
The Length of Day
You may think the change in water temperature or composition triggers their winter mode to kick in but, as far as we know, that would be wrong.
The point at which they are caught in the right conditions for water in their bodies to crystallize into ice. When Ice expands, it tears open cell membranes, making it game over.
The Slow Down
The point at which low temperatures reduce the flexibility and binding abilities of enzymes and cell walls no longer transfer metabolic processes. You know how butter spreads easily when at room temperature, then gets hard in the refrigerator. Now imagine the same butter at freezing temperatures. Cell membranes are essentially made out of the same compounds as butter, halting any flow of molecules through these buttery cell membranes. This lack of flow ultimately starves the fish of oxygen at the cellular level. What a tragic delicious way to go.
Luckily!, Arctic and Antarctic fish species have a few tricks up their sleeves (umm… or gills I guess).
Staying in icy waters can be devastating to life without the proper evolutionary adaptations. Since evolution works on a very strict trial and error strategy, the path of least resistance is always going to be getting out of town when brutally cold conditions start to creep in. For most fish species this is how they survive the arctic waters, they simply migrate away from them in something called “anadromous life-history”, which means they migrate away from the Arctic marine environment to freshwater for the winter where water temperatures tend to be mildly warmer.
Another (more direct), behavioural strategy used to not grow the ice tumours of death, would be to swim to deeper waters in the winter time. Remember how deeper waters have higher pressures? Yeah, ya do. Well, swimming to deeper waters puts a fish into the “No Ice” zone.
Ok, So this is where it gets interesting, and there are a few of thee so get ready for the bullet points.
In Contrast to us humans (and most other mammals) with our blood containing only one haemoglobin component (the part of blood that binds to O²), fish (and mostly cold water fish) have multiple components to their haemoglobin. There are many types of this process but, we only care right now about one. The one used by cold water fish, that is very temperature tolerant, but it reacts with a change in pH. Oxygen in these fish is thus transferred more directly with a change in pH.
Glycoproteins and Peptides²
Produced in the liver and pancreas, these ice seeking chemicals are sent out into the bloodstream and intestines. Entering through the gills and the cloaca (the butt hole), tiny ice crystals could cause certain death if left unchecked. Waiting for the ice, Glycoproteins and peptides begin to surround and attach themselves to the surfaces of each and every tiny ice crystal, making it impossible for them to grow in size to do real damage.
Glycoproteins cause another fun thing to happen called Thermal hysteresis (which is more of a side effect from the above process). This phenomenon causes the freezing point of a substance to be lower than its melting point. Wait, Whaaat? That goes against everything that Mr. biochem told me, and he was my favourite appropriately names teacher, is something you might say to yourself. How about an example? The winter flounder (Pseudopleuronectes americanus), in the winter, has a serum freezing point of -1.37°C, and a melting point of -0.75°C. So think about how that would look in your freezer and get back to me.
Fish Respiration, Steve F. Perry, Bruce Tufts Academic Press, Jul 6, 1998 – Technology & Engineering
DeVries,A.L.1983.AnnualReviewofPhysiology,45: 245– 260.