Fishkeeping is a popular hobby worldwide. So, fish are kept under favorable conditions in captivity. However, the same isn’t the case in the wild. In nature, fish are prone to extreme weather conditions. But can fish survive being frozen?
Fish cannot survive when completely frozen. The lakes, ponds, streams, and rivers don’t freeze completely. Ice forms on the upper layer, while there’s water beneath the surface where fish can survive. Fish lower their metabolism and the need for oxygen and food to survive the freezing temperatures.
Winter can be hard on fish. In cold winter months, lakes and rivers freeze, forming an ice layer over them. Yet, aquatic animals, including fish, manage to survive. There are various reasons behind this. With a bit of help from nature itself and the unique water properties, fish can survive under ice. So, let’s explore what makes a fish survive in icy water bodies.
Can Fish Survive Being Frozen In A Lake?
Fish can survive in a lake until it freezes entirely. They survive just fine under the ice as they have adapted themselves to survive in really low temperatures. Fish have evolved after experiencing the drastic annual temperature changes causing a variation in oxygen availability.
In the summer months, the lake’s surface water gets heated by the sun rays, while the water at the bottom of the lake remains comparatively cooler. As months pass by and winter arrives, the lake’s water temperature slowly evens out.
In extreme winter, the water temperature across the lake reduces, and the lake surface freezes. Since freshwater is maximally dense at 4°C (39.2°F), the water at temperatures below 4°C rises to the top of the water column.
This allows the water at the bottom layer to remain warmer, where the fish and other aquatic creatures reside and survive.
Also, once the lake freezes, fish start making adjustments to survive. They decrease their movements and slow down their metabolism. Reduced metabolism helps in conserving energy and also reduces the need for food. Some fish species, like catfish, burrow into the soft silt on the lake bed to keep themselves warm.
Now, fish can survive until oxygen is available. Fish usually breathe oxygen through their gills. Different species of fish have unique abilities to tolerate low oxygen conditions. Hence, when the lake freezes, some fish species adapt by absorbing oxygen into their skin, blood vessels in the stomach walls, guts, and swim bladders. In contrast, other fish species inhale the air bubble through their mouth that forms underneath the ice.
However, this is all possible till the time there is enough oxygen in the lake water. In shallow lakes that freeze almost to the bottom, oxygen depletes, and fish’s survival chances are minimized. Hence, when an entire lake lacks oxygen supply, winter-kill events take place. This is highly dangerous as aquatic creatures suffer a lot in this period.
In such scenarios, fish cling themselves under the ice surface. As fish are unable to inhale oxygen, they succumb to death due to suffocation.
Wow! That sounds great. Fish can survive in frozen lakes. But have you ever wondered if fish can freeze and come back to life?
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Can Fish Freeze And Come Back To Life?
Fish cannot come back to life if they are completely frozen. Having said that, there are fish in the Antarctic called alligator fish that sustain in the water below freezing point. This is due to the presence of glycoproteins, a substance in their blood.
Glycoproteins are known as ice-nucleating agents. They stop the spread of ice formation in the blood. Due to this, fish can survive.
Moreover, water is unusual in the sense that its solid form is less dense as compared to liquid form. Hence, water freezes from the top-down rather than the bottom-up.
This protects the fish residing at the bottom from freezing completely, even though the water at the surface freezes. A layer of ice at the surface acts as an insulator. So, the fish at the bottom gets enough oxygen to breathe and survive.
Besides, moving water also resists freezing. Hence, the rivers, lakes, and ponds seldom freeze completely till the bottom.
How Much Cold Can Fish Survive?
Fish have adapted themselves to survive the chilly winter. When ice forms at the top layer, the water beneath the ice remains at 4°C. The fish underneath can survive at this temperature until spring arrives.
Since fish are ectotherms, they rely on the environment to regulate their body temperature. Iced-in fish do not hibernate. Instead, they slow down their metabolism, thus reducing their need for food and oxygen to survive. They also lessen their activities and rest at the bottom, where the water temperature is relatively warm.
Alright! Now let’s understand what makes a fish survive under the ice.
How Do Fish Survive Under The Ice?
Fish are unique creatures that adapt well to a variety of conditions. They adapt themselves in extreme summer or chilly winter. During winter, most of the fish slow down. They become less active and rest near the bottom for survival.
As fish are cold-blooded creatures, their metabolism slows down when the temperature dips. In a resting state, their need for oxygen and food decreases. Also, slow metabolism results in slow respiration, digestion, and activity levels.
Besides, when water freezes and a layer of ice forms on the top of the pond, river, lake, or stream, it provides some insulation to retain the heat. Fish gather in groups and rest at the bottom as warm water sinks in cold freshwater. Since the bottom water remains warm, fish survive in it.
Coldwater fish can survive extremely low temperatures as they have antifreeze proteins called glycoproteins in their blood, which helps them withstand the cold.
Some fish species, like koi, burrow themselves into soft sediments to remain warm for surviving the harsh cold weather. Most of the fish become dormant and take a winter rest. Since fish are relatively small, they can warm their body faster and survive.
During winter, when ice forms on the top layer of the lakes or rivers, the water underneath does not freeze and remains in liquid form. Hence, oxygen gets trapped beneath the layer of ice, allowing the fish to survive.
Interesting Further Reading:
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Can koi fish survive being frozen? Koi fish can survive the entire winter in a frozen pond provided the water has sufficient oxygen. There are instances when koi fish has survived the entire winter in a frozen pond as the water contains enough oxygen for koi to survive. However, the water needs to be clean. If the water quality is poor, koi fish cannot survive for too long. This is because if the water surface freezes at the top, koi will not be able to come to the surface for breathing air.
Can koi fish freeze and come back to life? If koi fish freezes completely, it cannot come back to life. They will die if they freeze entirely. However, if the pond or lake is deep enough and only the top few inches of the water are frozen, koi fish can survive beneath it. Any fish, including koi, can survive as long as the pond or the water body does not freeze all the way through. In cold water, koi slow down their metabolism. They don’t need much food and inhale very little oxygen. As the water starts to warm in the spring, their metabolism speeds up.