Catfish Dying

Question
We have a 29 gal tank with one 11 year old catfish.  He has been doing well, until the last few weeks.  He has been beating himself against the glass.  We put a covering over part of the tank and this seem to help him.  Then we got some little koi and put them in the tank.  he ate everyone of them.  This was was last Friday.  He seemed fine, except he did not seem to care for his floating catfish feed anymore.  The last couple of days he started to loose his dark color and now is real pale.  Well we lost him.  It was quick.  I would still like to know if you have an idea as to what might have gone wrong.  Like I said he was 11 years old and we have been using the same water and doing the same cleaning for the last 6 years of his life.  I have no idea what could have brought on such a sudden change and would kill him so quickly.  Thank you for your time.

Venus

Answer
Saying he is a catfish is not a good enough description for me to really help you. There are hundreds of catfish commonly kept in aquaria.

It could also be those feeder fish. Never give any fish a feeder that wasn't quarentined properly. 9 out of 10 times they have an internal parasite that is sometimes passed on to the fish that eats them. The most likely thing is an internal parasite he got from one of the feeder fish is affecting him from the inside, hence that lack of any visible evidence on the outside.

Feed him foods that are enriched with garlic for awhile, but you will be lucky if it goes away. You should never really feed feeder fish, even if they were quarentined. They have no nutritional value anyways.

-Nick