WHAT HAPPENS TO POND FISH IN WINTER?

By: admin | Posted On: January 25th, 2011 | 27 Comments | In: POND FISH, Winterization

koi-under-ice

The warm weather is obviously the best time to be able to enjoy pond fish keeping. During this time pond fish and koi are active, lively, and highly visible. Many pond fish and koi become downright interactive with their keepers and will follow them around the pond, stick their faces out of the water or practically climb out of the pond to celebrate feeding time. During this time we all know exactly what is going on with our fish and all it takes is a quick peek into the pond.
Then the cold weather sets in and we slowly lose our ability to see what’s happening with our pond fish. Their activity slows down, they tend to keep themselves concealed, and once the ice and snow come; well, we lose touch with our fish. So what’s going on underneath those layers of ice and snow? What are our fish up to?
In short our fish are not up to too much. But pond fish not being up to too much is an interesting behavior all the same, given that they are so lively throughout the rest of the year. Koi and pond fish are poikilothermic animals, a fancy way of saying cold-blooded. This basically means that their body temperature is regulated by the surrounding temperature of the water, and their body functions respond and change according to the water temperature. The activity and metabolism of koi and pond fish is greatly reduced which is why they do not feed during the cold periods. Many experts say that because koi and pond fish are cold water fish they actually benefit from a cold period, however; prolonged cold spells are not good for them, they run the risk of their immune systems actually shutting down.
So what do they do? For the most part they sit on the bottom of the pond in the “warmest” pocket of water they can find. During winter months the warmer water is on the bottom of the pond as opposed to warmer months when the warmer water is at the top of the pond. I have often seen my koi lined up next to each other, facing the same direction as if they were in a parking lot! This is funny behavior that may lead to think that they are huddled together to share body heat; but since koi are poikilothermic that would not make sense, so this behavior is probably a way to fit as many koi into that pocket of warm water as possible. In larger warm areas you’d probably see a more random formation of the koi, some facing this way and others facing that way.
What happens to the koi and other pond fish is that they go into a state of torpor. Torpor is not quite full hibernation, because it is of a shorter duration than hibernation, but otherwise it is a very similar state of being: reduced body temperature, slowed metabolism, slow reaction times, reduced breathing rate and primary body functions. Torpor allows the animal to save the energy that would otherwise be needed for higher levels of activity. Because of the state of being in torpor it is a very good idea to keep things as calm as possible around the pond. If you need to open the ice in the pond find a quiet way to do it like using boiling water to open a hole, don’t chop it open with a pick ax! Even using a hand held drill with a hole saw is actually pretty quiet compared to other methods, and if the ice is too thick to open with boiling water the hole saw is a great tool to have. To maintain an open area in the ice try using a floating de-icer or an aerator. This open area in the ice will allow noxious gases, like ammonia, to escape from the pond.
Some people add salt to their ponds. I personally am not a practitioner of adding salt unless it is for treatment purposes, but if you do add salt to your pond you should dilute your salt levels during cold winter months. The salt can make your pond water’s freezing point drop to below 30F which will kill your fish. Generally speaking you should not let your pond water’s temperature drop below 34F. Temperatures below 34F will allow ice crystals to form on the gills of your koi, which can kill them, so watch the temperatures if you live in an area of extreme winter temperatures.
If your pond is cleaned and prepped prior to those cold dark winter months, then worry not, your koi and pond fish should do just fine. Like was mentioned the koi, goldfish, and pond fish in your pond do not DO much during the winter months. Spring will be here soon enough and your fish will start again with their antics and amusing behavior. But for now you have a better idea of what is happening out there under the ice and snow, and you are not missing out on any party. If only we could share that state of torpor and wake again when the spring has sprung!
The LOVE YOUR POND blog is written by Mike Gannon of Full Service Aquatics. Mike is a professional pond builder and expert in the broad topics of fishkeeping and water gardening. Mike also produces THE POND HUNTER video series which can be viewed on Youtube. “In The Pursuit Of All Things Aquatic” the Pond Hunter videos provide how-to pond construction videos, pondumentaries, and videos of related interest. Mike resides in Summit, New Jersey with his wife and 2 daughters. To visit his website go to www.loveyourpond.com and visit The Pond Hunter at www.youtube.com/thepondhunter. All copyrights to this material belong to Mike Gannon.

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  1. Eleanor Says:

    on February 23, 2013 at 9:42 am

    Hi, is the image ‘koi-under-ice’ copyrighted? I am aking as I am doing a koi fish project and we can only use copyright free images.
    Thank you
    Eleanor

  2. Mgannon Says:

    on March 2, 2013 at 3:57 pm

    Hello Eleanor, that photo is not likely copyrighted. I too try to use non copyright images, but I’d doa google search just to be sure!! thanks for reading the blog. Mike

  3. Ginger Says:

    on September 2, 2013 at 9:59 pm

    Hello Mike,
    Someone gave my son pond fish as a present, and because we are renting at the place we are living, there is no space for the pond fish to be inside in a tank. So, I have an idea of using a large planter that is approximately 40″ (plus) diameter to use as an above ground pond. Would a planter serve as an adequate pond for pond fish?

  4. Mgannon Says:

    on September 3, 2013 at 1:44 pm

    Hello Ginger,
    Thanks for getting in touch! Before saying that the planter will work, it needs to be considered what material the planter is made of. What type of pond fish are we talking about? What type of climate do you live in and will this be a year round housing for the fish? I have seen many patio ponds that have fish in them but cannot function year round because of cold weather conditions, or even very hot conditions. In all I’d say it is not the most ideal situation for fish keeping, but not impossible either as long as the conditions are right.
    Mike

  5. Karen Says:

    on September 9, 2013 at 9:47 pm

    I am a biology teacher considering an environmental club project to remediate an algae filled pond in a local park (central NJ) by seeding with duckweed and using Koi to feed on it. Do you think koi are hardy enough to survive winters here untended? I don’t know how deep it is, but that is one of the things the kids can investigate, I would be very grateful if you could give me some pointers.

  6. Mgannon Says:

    on September 10, 2013 at 12:47 am

    Hello Karen, that sounds like a great project. I’d need a bit more info to give you good advice, but generally speaking the koi will be winter hardy. Feel free to give me a call, I am also based in NJ and would love to discuss your project. Call Mike at 908 277 6000!

  7. Eve Brady Says:

    on September 10, 2013 at 9:52 am

    Hello,

    I have a pond which is very deep (about 4 ft) but last year in Norfolk it was so very cold and in the early spring two of my lovely fish died, they were quite old though so I am not sure f they simply reached the end of their life or died because they just couldn’t cope with the freezing temperatures. They have lots of shelter as I have used square sley type material drain pipes …(have used them for year and the fish love to hide in them and swim through them!) The water never completely freezes over as I keep the pump running which powers the water fall too so there are always two areas which are ice free, I am however still a bit concerned about the winter months this year, should I cover part of the pond with bubble wrap or something similar to maintain an element of heat?

    Looking forward to hearing from you,

    Kind regards,

    Eve

  8. Mgannon Says:

    on September 10, 2013 at 2:09 pm

    Hi Eve, I don’t think that it is necessarily an issue of higher winter temps that you need to have. I think with typical de-icer/aerator equipment during winter you should do just fine; and the many years of trouble free winters would support that. I cannot say why your fish passed but I don’t see reason to insulate the pond any more. Be sure you give your pond and filters a good cleaning before winter hits, and add more aeration if you need it! Mike

  9. Brittany Says:

    on September 23, 2013 at 2:43 pm

    we recently bought a house, and in the backyard there is a koi pond and there are maybe 10-15 fish in the pond. i’ve been reading on what i should do, but i’m still not 100% on what steps i need to take to get it ready for cold weather. it has a waterfall and a hand built filter system. i do have a heating rock to put in the pond. i wasn’t sure if there were any chemicals or anything like that that i needed to put into the pond. i know that they can survive the winter if the pond is prep properly. wondering if you can give me some helpful hints.

    thanks so much
    brittany

  10. Mgannon Says:

    on September 25, 2013 at 1:52 am

    Hey Brittany,
    thanks for getting in touch! Some systems can run year round, others need to be shut down. You can use cold weather food for your fish and feed until late October typically, and you can also use a cold water beneficial bacteria treatment during winter months. If you search on the LOVEYOURPOND blog a bit you will find tons fo great info on how to handle your pond during the winter and how to prepare your pond for those winter months too. Try using the search function for what ever questions you may have and you’ll likely find an answer! Thanks Mike

  11. Mike Says:

    on October 21, 2013 at 8:20 pm

    Hi I live in California and the current temperature is about 82 degrees. I cleaned my koi pond and I think I may have inadvertently woken the koi from their Torpor state. The koi are back in the cleaner pond but are all at the bottoms and lifeless. I can’t tell whether they are hibernating or dead :( . Any way to tell if I am an accidental mass murderer or not?

  12. Mgannon Says:

    on October 22, 2013 at 7:03 pm

    I am hoping for the best for your fish Mike. It should not take too long to know if they are dead or not unfortunately. If the temperature is 82 however; I don’t think your fish would be in a state of torpor. Hoping for the best! Mike

  13. Dave Says:

    on October 22, 2013 at 8:26 pm

    I have a small pond in Wisconsin. It’s about 3 ft in diameter, and 20 in deep at deepest. It has hardy lillies, and 3 goldfish – each about 3-4 inches long. I was going to bring the fish in for the winter and keep them each in a fishbowl. Problem is I can’t find them to move them to a fishbowl. Water is getting colder – I estimate it to be between 40 and 50. I’m afraid to leave them all winter, as the pond may freeze solid except for the deepest which may not be enough water to sustain them.

  14. Mgannon Says:

    on October 22, 2013 at 10:46 pm

    Hey Dave, it can get pretty cold in your area. I’d recommend trying to bring in the fish for the winter based on the size of the pond that you are describing. If you can’t then its a good idea to put in a de-icer or aerator. Let me know how you do! Mike

  15. Scott Says:

    on November 6, 2013 at 3:16 am

    I live in Central Wisconsin with a 150 to 200 gallon pond, with a depth of 19 inches. Should I try to heat and aerate this pond, to over winter the fish? Thanks, Scott.

  16. Scott Huntley Says:

    on November 7, 2013 at 1:51 am

    We have 150 to 200 gallon Koi pond about 19 inches deep and live in Central Wisconsin. Should I spend time and efforts trying to over winter my koi or will my pond still freeze solid?

  17. crystal Says:

    on November 7, 2013 at 10:06 am

    we took our fish out our pond and put them into fish tank into are house for the winter but they’re slowly dying did we take them out too late we had our first snow storm the snow melted and thenwe put in our house in the fish tankdo they need bubbleshopefully you get back to me as soon as you can so I know if we did something wrong before they all die my little girls are sad about it

    Thank you crystal j

  18. Mgannon Says:

    on November 12, 2013 at 10:27 pm

    Hey Scott, yes I’d recommend aerating and de-icing your pond during the winter months. Mike

  19. Mgannon Says:

    on November 12, 2013 at 10:29 pm

    Hi Crystal, I’m sorry to hear that you lost fish. I don’t think that bringing your fish in would have made them die unless they were not acclimated correctly. I am guessing that perhaps there was an ammonia spike in the new water and that may have killed your fish, but I am only guessing because there is alot I don’t know about the situation. Sorry again! Mike

  20. Dallas Clark Says:

    on November 23, 2013 at 12:23 am

    Question:
    My 2800 gal pond with waterfall with 14″ curtain pushing only 2000 GPH pump and my water is getting a white tent like an algae bloom in this cold weather, filters are clean, but, with a little sludge on the bottom (got behind due to wife on HOSPICE) Have 8 Koi about 7-8″, all readings seems A -OK or within range. Have been a Koi Keeper for 3 years
    and lost two beautiful Koi today. White tent of water is telling me what?
    KoiWrangler, Dallas

  21. Lydia Says:

    on December 10, 2013 at 7:03 pm

    I live in Danville, CA and this winter is unusual here in the SF Bay inland suburb temp has fallen to 20 degree F for a few days now. I see their gills moving. The two oldest are at least 30 years old, I inherited them 12 years ago and the prior owner could not recall exactly when he put in the pond so this is the estimate; they were elderly and he said they can live to 100 years! They are huddled together; they always hang out together like a married couple and sleep next to each other their “snouts” inside the where the UV filter is.. One of the larger ones that is by itself and is about 5 years old and almost matches them in size already black and orange with fancy tail – obviously I am no expert! I also have smaller ones that I received as a gift from the person who used to service my pond before he moved to Florida. This cold snap has lasted so far 5 nights with last night being the coldest and will probably last another two then go back to the 60s in the day. The water has a lot of foam but no ice. Is there anything that I should do? The waterfall is running. I have not fed them in a week. I typically feed them once week in the winter here.a small quantity of food. I was told to change the UV lights every other year. I do not have a new koi pond person He cleaned out and drained the pond every year and scrubbed it. I doubt most people will do that. What is the typical maintenance routine and charge? I have a pond filter, modern. that he installed a few years ago and a waterfall that is currently running. Basically I buy shrimp meal food from an installer of koi ponds from Southern California in bulk that i met on eBay for a very good price I have about 11 fish now. When I got the pond with the house in 1999 there were 40 fish including gold fish but something happened insecticide by a careless gardner not sure so only the largest two survived. a very sad day. I bought the one I described I call Barbie because it is so beautiful from Hawaii during the recession and one from North Carolina that really looked like common carp that died and grew so fast just one day floated to the top I thought that koi floated to the top when dead not stayed at the bottom. All those that died were at the top so I was surprised that you told the other California person that he would find if the fish at the bottom were dead. I have seen 38 die excluding Mr. North Carolina. One thing I learned is that when we had an island in the middle we could not have small koi the birds ate them and Loi the person who took such good care of my pond told me to remove it because the birds may have used it to “fish” and sure enough, after that for the first time I had small fish that survived! One time I was surprised to see a stork on my pond at 6 :AM that must have escaped from the Oakland Zoo. I thought a small aircraft was over my pond and I screamed! Since they are only in the Gulf of Mexico, it must have come from the zoo! Luckily I saw it.

    The former owner had blocks of salt that they used for the Koi and all sorts of medicine but none of that has been necessary. Any comments would be appreciated since I am not expert but am quite fond of my fish. I work out of my house and they take me outside. I pull out the leaves manually and spend some time out there and also clean out the filter rinse, backwash at least once a week. Anything else I should be doing? We have algae now., more than before on the rocks. I hate using the chemicals the fish do not appear to like them.

  22. Grace Says:

    on January 2, 2014 at 1:50 pm

    I have a 250 gal pond I put a few goldfish in. Every year the resident hawk gets them. My last set has lasted almost 3 years! Yeah. It is January in Atlanta and cold, not freezing. Currently one of the large fish is lying on the bottom looking dead. I went to remove him and he moved. I figured he is a goner. Then, 3 days later, he hadn’t moved and is on the bottom under some leaves. I went to remove him again, yikes, still alive. I guess he might live, I thought it was a swim bladder issue. this behavior is bizarre and no where on the web can I find this as normal. They have 14 babies I plan to give away this spring to the local kids. Too many fish for this pond. Thanks for the article.

  23. Mark Says:

    on March 25, 2014 at 12:16 am

    Hi, I moved into an old home approximately one year ago and inherited a pond with three koi and three goldfish. Since then my wife and I have done everything we thought possible to keep our pond healthy (we have a filtration system, pump, waterfall, we purchased a new deicer, feed them above 45º-50º, add small amounts of PH balance occasionally, etc) but unfortunately two of the three koi died within one day of each other this February. The third one is currently lying on its side and it looks like he’s not going to make it either. Several days ago I thought it was dead but when I went to lift him out with the net he flapped slightly. I went back again this afternoon and it appears to still be hanging on. I’m scratching my head over this because the three goldfish appear to be doing well.

    I have a few questions:
    1. Is my fish dying or is it hibernating? It doesn’t appear to be hibernating/sleeping since it’s on it’s side and very weak when it flapped.
    2. Is there anything I can do to help bring it back to health?

    Please let me know. Thanks.

  24. Mike Gannon Says:

    on March 25, 2014 at 10:21 pm

    Hello, thanks for getting in touch. I’m very sorry to hear about your fish loss. The remaining koi sounds like it is in a state of stress, not hibernation (or torpor, as it is called with fish!) The smaller fish may not be stressed mostly because their body mass is much smaller and changes in environmental conditions are tolerated better. It is very difficult for me to say exactly why you lost your fish without alot more information; however since you are a new pond owner you should know that fish loss is not a typical problem. I believe it must be an environmental issue given the proximity in time that the other fish had died, and probably not necessarily disease related.
    I would add a bit of pond salt to a therapeutic level, which is about 1/2# salt per 100 gallons. You can use solar salt that is also used for water softeners to save a bit of money, or just buy “pond salt” its the same thing. Also add some additional aeration, then wait and see how the koi does. Don’t bother it or poke at it, just give it time; it will either recover slowly or …not.
    Good luck, and if you need anything else just let me know!
    Mike

  25. Mark Says:

    on April 1, 2014 at 3:13 am

    Thank you Mike for your reply. This is very helpful to read. Sadly, all three koi were lost. Your tips are useful regardless. We’ll know for next time and hopefully be better prepared.

    -mark-

  26. Protecting Your Pond In The Winter | All Pond Solutions | All Pond Solutions Blog Says:

    on April 28, 2014 at 3:28 pm

    [...] Pond fish virtually hibernate in the winter months because their metabolism is controlled by the temperature of the water. This means that you should start reducing the amount of food they are given as the weather gets colder. You can stop feeding them completely when the temperature drops below 4oC. [...]

  27. Mike Gannon Says:

    on May 11, 2014 at 3:44 pm

    Hey, thanks for the comment!

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