Sick fish/some dead

Question
Hi Chris,

My wife and I inherited a 50 gallon freshwater tank from some friends who moved away with what they called freshwater parrot fish. There were six of these fish along with 2 small catfish looking fish and 2 eel fish.  We have had these fish for about a year with basically no problem.  During that time only one of the parrotfish died and it was the smallest of them.  However, last night we noticed that the fish were all swimming up at the top of the tank which is very unusual.  They also seemed very listless and unresponsive.  We just thought they were sleeping.  When we awoke this morning 2 of the parrotfish both little catfish and both eel fish were dead. The other 4 parrotfish were still breathing but were completely catatonic and laying on their side.  We took them out, changed out the water and then put them back in.  They are still breathing but are motionless.  If we touch them they do swim a little but then they stop and just sink back down to the bottom.  Do you have any idea what happened. This all happened overnight and there was no behavorial warning other than the swimming at the top.  Please help if you can.

Thanks
Pat  

Answer
Hi Pat;

That's a shame. What a terrible trauma for all of you.

It sounds like either a water quality problem or a disease hit. Since the old water is gone and you can't test it to see if there was a problem, let's make sure it isn't a disease;

Look at the fins and the skin. Are there any dots, spots, blotches or lesions anywhere? Scales missing? Ragged fins? Anything else that looks unusual?

Look at the gills, not the outer plates that protect the gills, but the gills themselves underneath. You may have to net a fish out of the water for a moment and lift a gill plate with your wet fingernail to see. The gills should be bright red and uniform in color. If there are any light patches or tiny little creatures attached, they have parasites or gill disease.

All tanks need a 25% water change weekly, especially those with large fish. Gravel vacuuming every 2 to 4 weeks is important too. Without regular water changes, dissolved wastes build up and the buffers that keep pH balanced are used up. The water becomes more acidy all the time and the biological balance in the filter system crashes.

On the other hand, overcleaning can be a problem as well. If the filter was recently changed or cleaned, all the beneficial bacteria that consumes the waste was killed. This can cause a spike in nitrite and/or ammonia. Here are two links to web pages about that;

http://freshaquarium.about.com/cs/disease/p/ammoniapoison.htm
http://freshaquarium.about.com/cs/disease/p/nitritepoison.htm

Hopefully they will start feeling better now that the water was changed, but watch for other symptoms. They are in shock right now. Just keep the room quiet and wait. It's about the best you can do right now.

I hope they feel better very soon......

At Your Service;
Chris Robbins