Pond Fish Behavior: How do tell if my fish are healthy?

If you have a pond, you probably have fish and if you have fish you might get concerned when their behavior changes. I am asked often about pond fish behavior. Especially this time of year, I get questions such as, “they hide a lot…”, “They stay at the bottom and don’t move much…”, “…is that normal?”. Understanding what behavior is normal and what behavior needs attention will help you recognize when it is time to call an expert. Backyard ponds can be inhabited by all different kinds of fish. But I will be addressing the general behavior of koi and/or gold fish.

Cold Weather

In cold weather, it is normal for fish to stay in the bottom of the pond. If you have a fish cave they will often bunch together inside in a dormant state and they will stop eating. If your fish are hiding away and acting sluggish in the cold winter months and not coming up to eat, don’t fret. This behavior is normal. In fact, in temperatures 40 degrees Fahrenheit and below you should stop feeding them. It is unhealthy for their digestion.


Koi are friendly fish. My koi love to beg for food every time someone approaches the pond, much like a pack of dogs begging for treats. However, when a koi is introduced to a new environment it will take time for them to adjust. If you have just added your fish to their new home, don’t be surprised if they are skittish and dart away or hide when you approach. Koi that have been interactive in the past but are now acting skittish, may be a sign that a predator has been about. If you live near a large body of water, then your koi may be in danger of blue heron.  If this is the case, you may want to keep a close watch on them.  You could even net your pond until the threat is gone.

Environmental Change

Koi can be stressed by a sudden change in environment.  This could be a rapid water temperature change, or a relocation from pond to tank or vice versa.  If stressed, it is normal for them to ignore food that you may throw out for them, or act lethargic and stay low in the water. Overpopulation can also cause fish stress, as well as pollution in the water from runoff.

If your fish act stressed seemingly without cause, you should check the chemical levels in your water. Testing kits are usually available anywhere that sells pond or aquarium equipment. Other signs of stress include bloodshot fins as well as rubbing against surfaces which causes scales to break off. If your fish are leaping a lot and/or gasping at the surface for air, the level of dissolved oxygen may be too low. You will want to add some type of aeration as quickly as possible to prevent suffocation.

When your fish are stressed it lowers their immune systems and can open your fish up to health issues. Some behavior that indicates a sick fish includes sluggish or clumsy, uncoordinated swimming, or speeding around rapidly as if panicked. If your fish are displaying any of this behavior you should call an expert to come by and check on them. If you have pond fish behavior or health questions, feel free to give us a call.

Catch you downstream.

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