How to Tell if a Fat Koi Fish is Pregnant or Sick

Part of taking care of your pond is taking care of your Koi fish. Has one of your Koi Fish in your pond suddenly gotten fatter than the rest? Are you wondering if there may be little fish in your pond soon? This article will help you determine if you have a mama fish on your hands, or if something else is going on.

Step 1

Take a good look at the fish that you think is pregnant. Actually, Koi fish don't get 'pregnant', and aren't 'live-bearers'. But, they do look fatter when they have eggs developing- usually in the spring or summer. Does the fish look fatter than the other fish in the pond? Does it look fatter, or does it look bloated?

Step 2

Look at the behaviour of your other Koi fish. When female Koi have developed eggs, they have to be pushed out of her body. Usually this means that the males will chase her around and essentially bash her against the sides of the pond. When she expells her eggs, the males can then fertilize them. They can get quite aggressive about this, and it can go on for hours- even days. it's possible your female can get hurt. It isn't uncommon to have Koi fish actually leap out of the pond during this activity. So, observe your fish. Are a lot of the fish chasing one fish? Are they pushing the fish against the sides of the pond? Is your fish swimming slower than normal?

Koi Fish with Bloat, Dropsy or Pine-Cone Syndrome click to enlarge

Or, is your fish just fat? That is really more of a problem. If your Koi fish suddenly gets fat, and none of the other fish are chasing it around, there's probably only three reasons. The first is that all of your fish are female, and that the fat one has eggs that are 'stuck' inside her. The second is that you are overfeeding your fish, which eventually will make your pond dirty and unhealthy. The third is that your fish has what is called 'Bloat', 'Dropsy', Pine-Cone Syndrome' or the 'Malawi Bloat'. You can tell if they have this because, as in the picture above, your fish will be so bloated that their scales actually stick out, making them look like a pine-cone.

Step 4

The only thing a hobbyist ponder can do for a koi that has stuck eggs is to wait it out. While there are medications that can be applied to a fish that has Bloat, they don't really have a track record of success. Expert opinion regarding bloat is that most Koi will eventually die from it. There is some conflict with experts about its cause and the best treatment. But in some cases, for no known reason, the fish will get better on its' own. Providing a medicated fish food may help non-professional Koi enthusiasts. It's a safe bet that having a clean koi pond, a clean koi pond filter, having proper salt/electrolyte balance, not introducing infected fish, and feeding a healthy diet might be the key to a fish recovering on it's own.