Bala shark

Question
Our 6inch male bala shark is behaving erratic.  He is keeping his head down, and is jerking as if he is trying to spit something out of his mouth. If the tries to swim properly he goes into jerky fits.  He has stopped eating, but I think its because he can't work out how to get to the food in his state.  He has been like this for two days now.

The other bala shark (we think female) stays near him, but she is fine and swimming normally and eating normally.

The tank is 140 litres and has a hood.  It has a few mollies, guppies, 2 small black widows, a gurami (medium) and 4 small flying foxes (babies) and a few small snails.  The baby mollies are just big enough now that they are going to be moved on so the tank doesn't get crowded.

Dad did a water change 3 days ago (25%) checked all levels and they are spot on.  All the other fish look ok, behave ok.  Dad put in multicure yesterday just in case the bala shark has something parasitic etc.

I think the shark has something nurological going on. Either from jumping and wacking its head on the hood, or from a disease or soemthing - tho there is no sign of injury to the body or eyes, no spots or itch etc.  Dad thinks he might have something stuck in his mouth/gills as he has seen him swallow up to three pellets at a time when eating.  But I would have thought after two days the pellet would have broken down by now.

What do you think?  worried we are going to loose him.

Answer
Hi Cate!

It could be stress. Gasping, loss of appetite, and awkward swim patterns are symptoms of stress. Since its winter, the water temperature could have dropped and caused temperature stress. Try the API Stress Coat. It's available at Petsmart or Petco.

-Sam