lyretail molly acting strange

Question
Hello Nathan,

I have a 20 gallon tank with 15 lyretail molly and 1 Pleco - Suckermouth catfish. Things have been generally good for the last 6-7 months. I have been doing regular water changes (every 3 weeks) and filter cartridge changes (every 2 weeks).

Since 3-4 days, one of my lyretail molly has been acting and swimming strange. It stays vertical and keeps swimming in circles staying vertical. I immediately did a water change, filter cartridge change and added some mardel anti-bacteria medication. I did not see any change in the behavior after a day. I tested for nitrate, etc and all looks good. Also today morning I saw one more molly showing the same behavior and the other one still behaving same along with signs of loosing balance.

Not sure if my description is clear. Thanks in advance for the help.

Regards,
Darshan

Answer
Hi Darshan,

Your Molly may be suffereing from Swim Bladder Disease. The swim bladder is a gas-filled organ in the fish, and by letting air in and out, it can either go to the top or sink down. The common symptoms are difficulty swimming, 'losing balance', and especially trouble swimming to the bottom.

It can be caused by constipation, or a bacterial infection. You may want to try feeding a defrosted pea to the Molly. Cut it in half so that he/she can have access to the interior. Peas have been known to cure Swim Bladder Disease.

Perform 10-20% water changes daily until the problem resolves. You can keep using the medication. Most diseases heal after a week. Nothing significant will happen after a day.


One last thing - Your tank is VERY overstocked. You have too much fish in there. An excess of fish contributes to poorer water quality, even with a good filter. Even though they may seem fine, they may die prematurely and become more susceptible to disease. The most you could have in the tank are 10 Mollies at most. You should never have more than half the number of fish as your tank's size (10 max small fish for a 20 gal), (10 is half of 20).

But, the most important thing is that the Pleco is, unfortunately, not suitable to your tank, unless it's a Bristlenose Pleco. If it's one of the ones you most often find in pet stores, it's a Common Pleco, which will grow to 24" and is not suitable for your tank. You will need to find a new home for it.

Good Luck, and Happy Fishkeeping!