hiding swordfish

Question
We have a 50 gallon tank with 10 fish.  We do a partial water change once a week and the pH levels etc. are perfect.  All of a sudden our mail swordfish is acting shy and hiding in the corner of the aquarium.  He does come out to eat and then retreats.  Previously, he had been very active.  We can see no visible signs of problems.  Is he sick?  Thank you for all of your help.

Answer
Hi Sally;

Sometimes fish intimidate each other and one or more needs to hide. Are there other males in the tank? Maybe one that was previously a juvenile that has now matured? Or, have you added any new fish lately? You could add more decorations or from time to time just rearrange the ones you already have. It helps to break up any territorial disputes that may be happening in there.

I would just continue to watch him for signs of illness and isolate him if he shows something.

At Your Service;
Chris Robbins