molly struggling to swim

Question
Hey Karen,

I have a mature 60 gal tank with a variety of active healthy fish.  One of my three mollies, the female, appears to be having trouble both swimming and maintaining buoyancy.  She spends most of the time on the bottom of the tank or on rock structures.  I cant see any ich or other signs of disease on her.  She does eat.  She appears to be breathing relaxed.  She will take short swims around the tank but appears to sink tail first to the bottom in a short time.  Her fins appear to moving okay.  Ideassssss?????

Answer
Hi Dan,
Poor molly. She may have swim bladder trouble. The swim bladder is a special organ that most fish have which is responsible for controlling their equilibrium and some of their swimming. If something interferes with it, the fish can swim very awkwardly and some fish even float helplessly at the top. There are many things that can cause swim bladder disorder. Diet is one of the number #1 causes. Overfeeding or feeding too much dry food at one time can cause the fish to have swim bladder disorder. This is due to the dry food swelling up with water inside the fishes digestive system and putting pressure on the swim bladder. Sometimes fish can even get constipation which often causes swim bladder problems. Not offering enough vegetable matter can often be the cause. The best remedy is to fast (not feed) the little fish for at least 1-2 days and then offer a thawed and shelled green pea soley to the fish for a couple of days.

But swim bladder disorder can also be caused by injury, bruising, or something internally going wrong. And there's not much you can do about it unfortunately.

Also your fish may be slowing down from old age also. If your fish is a few years old then this could be the reason for her behavior. Sometimes female mollies live for only a year, especially those who have been stressed by males or from having large broods of fry.

Best of luck, I'm sorry about the bad news though.

Happy holidays,
Karen~