Ah, the frozen fish stick! A quick “go to” meal for parents on the go that kids love. A nostalgic comfort food for tons of adults. The perfect—and perhaps the only—vehicle for the tangy creation that we call tartar sauce. Fish sticks rely fully on a manufacturing process, because, as we all know, even water resources in the coldest of arctic regions do not supply fish nicely frozen and ready to go. Exactly why is it that fish—whether used for food items or not—emerge from the cold of winter not only unfrozen but also unharmed?
The answer has everything to do with water. The combination of water’s ordinary and unique properties, along with “fish physiology,” allows all types of water species to survive in winter-cold waters, even when those waters freeze over.
First, let’s look at one of the most commonly known properties of water. It’s made up, in part, by oxygen—and because fish are equipped with gills instead of lungs, fish are able to “breathe in” water and extract the oxygen they need to live. This happens regardless of the water’s temperature, be it during the high summer heat or the chills of winter. In the winter, fish metabolism does slow down. As cold-blooded creatures, fish lower their body temperature to match the water around them as it cools. With lower metabolism and activity, a fish requires less oxygen and nourishment, which, as we’ll learn below, can be a lifesaver during the winter.
A more unique property of water is that, unlike most materials and matter, water expands instead of contracts as it cools. This frozen water, which you know as “ice”, that forms on the surface of lakes, ponds and the like further contributes to fish survival by 1) acting as an insulator and trapping heat in the water below it; and 2) acting as a barrier that traps oxygen below. In other words, water freezes as a less dense substance, thus helping to ensure that fish have ample oxygen to live and that the water doesn’t get too cold for fish to survive—or freeze entirely.
Ice is also less dense than water (I know it sounds strange since ice is harder than water, but it’s a “space between the molecules” thing). The density changes that water undergoes as temperatures change causes a “thermal turnover” process, as the seasons transition from summer to fall to winter. The process is a bit heavy on the science and is detailed here. But to sum it up, this process has warmer water—which resides on the surface during the summer—cooling and circulating down as it approaches a “maximum density” temperature, then rising back up. This circulation process infuses and distributes oxygen throughout the water—preparing the water for fish survival once ice begins to form at the surface. Moreover, one problem with frozen water is that it prevents sunlight from reaching aquatic vegetation below and therefore limits these plants’ ability to produce oxygen through photosynthesis. Without plants infusing oxygen into the water during the winter, thermal turnover and the resulting oxygen production can be extremely important to what is living under the ice, especially in prolonged winters.
Lastly, I’ll mention a fact I find fascinating: Water on the verge of freezing or that has begun to freeze responds to a natural antifreeze that scientists have discovered that fish in extremely cold environments are able to produce. Because this antifreeze and water work the way they do, fish are never completely surrounded by ice. In other words, the antifreeze is the ultimate preventer of a naturally produced frozen fish stick!
So the next time you dig into your fish stick brand of choice, take a minute to appreciate yet another role water plays in maintaining the natural order of things in our world.