Is My Koi Fat or Pregnant?

Many koi owners often wonder if their beloved fish is simply overweight or if it’s actually pregnant. While it may be challenging to determine without professional assistance, there are a few key indicators that can help you make an educated guess. In this article, we will explore the signs that can help you differentiate between a fat koi and a pregnant one.

Physical Appearance

Koi that are carrying eggs will exhibit a rounder and more swollen appearance compared to their non-pregnant counterparts. This is especially noticeable when viewing the fish from the top. Their belly area will appear larger and distended, often giving them a slightly bloated appearance.

Behavioral Changes

In addition to physical changes, pregnant koi may also exhibit behavioral alterations. They might become more reclusive and prefer to spend time in isolated areas of the pond or aquarium. Pregnant koi may also display decreased appetite or even stop eating altogether as they focus their energy on developing eggs.


If you notice your koi isolating itself and refusing food, it might be an indicator of pregnancy rather than obesity.

Egg Spots

Pregnant female koi develop small white spots on their ventral area known as “egg spots.” These spots are actually deposits of mucus that assist in the fertilization process. The presence of these spots can help confirm pregnancy in female koi.

Consulting an Expert

If you’re still unsure whether your koi is fat or pregnant after observing these indicators, it’s always a good idea to consult an expert. They will be able to provide you with a definitive answer based on their experience and knowledge.


Determining whether your koi is fat or pregnant can be challenging but not impossible. By carefully observing their physical appearance, behavior, and the presence of egg spots, you can make an informed guess. Remember, it’s always best to seek professional advice if you’re unsure.

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Emma Gibson