What is the water quality like (ammonia, nitrite, nitrate & pH)?
How long has the tank been running for?
How often do you do water changes and how much water do you change?
Do you gravel clean the substrate when you do a water change?
Do you dechlorinate the new water before adding it to the tank?
What sort of filter do you have?
How often and do you clean the filter?
What are you feeding the fish?
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The fish appears to be in good condition and does not show any external signs of disease. The most common cause of fish health issues is poor water quality. If you are every concerned about the fish's health or behaviour, do a 75% water change and gravel clean the substrate every day until the fish acts normally or until the problem is identified or resolved.
The following link has information about what to do if your fish get sick. It's long and boring but worth knowing. I recommend printing it out and reading it in bed to help fall asleep.
https://www.fishforums.net/threads/what-to-do-if-your-fish-gets-sick.450268/