Do Fish Hibernate?
Fish are ectothermic poikilothermic vertebrates, which is a fancy way of saying they are cold blooded organisms. They rely on their surrounding environment to help regulate their internal temperatures. If your pond water cools down, your fish will too!
What is Torpor?
During substantial temperature shifts, like the winter season, fish enter a low-energy state that reduces their food requirements. This state is commonly referred to as “hibernation,” however; fish don’t technically hibernate. They actually enter a state known as torpor. This looks similar to hibernation, but is a lighter, more temporary state that typically lasts anywhere from a few hours to a couple of weeks. Torpor allows fish to “sleep” for longer periods of time followed by a brief period of food foraging. During torpor, heart rate will slow down, oxygen consumption will decrease, and brain activity will be reduced.
This phenomenon explains why you don’t need to feed your fish as much during the winter. As their body temperatures cool down, their metabolisms begin to slow as well. This is because less energy is required for fish to maintain the same cold temperature as the surrounding water. Additionally, during torpor, hormones are released that suppress appetite. For most fish during winter, simply grazing on plants or algae in the pond is sufficient.
Coming Out of Torpor
Pond fish will naturally come out of torpor once temperatures warm back up. This will likely be during springtime, however; there have been instances of fish coming out of torpor during mild weather periods in the winter months. Fish will fall in and out of torpor as temperatures fluctuate.
Once temperatures begin to exceed 50ºF regularly, your fish should naturally regain normal activity levels, feeding patterns, and alertness. It is important that you do not attempt to “wake up” the fish yourself. This could cause shock, injury, or the usage of precious energy reserves that are still needed for the fish to naturally revive itself in time.
As fish exit torpor, their appetites will slowly return as their metabolism speeds back up. A good sign that your fish have fully come out of torpor is if they are swimming around your pond, likely in search of food to satisfy their newly returned hunger.
Pond fish do not hibernate. Instead, they repeatedly enter a state known as torpor which allows them to conserve their energy during the coldest periods of winter. Torpor is a state which fish naturally regulate on their own in response to their surrounding water temperatures. Never try to “wake” a fish out of torpor, especially during the height of winter. As long as you allow your fish to self-regulate on their own accord, they’ll wake in the spring excited to resume their normal activities in your water landscape.