Possible disease affecting my yellow perch

Hi. Have a 1100 gallon aquarium with 15 full size (about 10" each) yellow perch. I've had them just under 3 years from 1". One by one recently they have started dying. They stop eating, seem to loose their swim bladder (sinking to the bottom) then start to swim eratically around the tank as if they've been stunned, then eventually die. Symtoms seem to last about a week. I have been feeding them primarily frozen smelt since I've had them. I do about 200 gal. water changes every week so I'm not concerned about water quality. Has anybody seen anything like this before?

Holy cow, 1100 gallons! Can you share photos/video of your tank? Sorry to hear about your fish. A necropsy might help you determine the cause. Here's a dichotomous key: http://www.fishyfarm...im_bladder.html

I don't know anything about the disease, but I also would be interested in hearing more about the tank.

It's a plywood tank, 2 layers of 3/4" plywood with the inner layer good one side facing inwards. The interior is painted with black Intersil epoxy paint. The front is a walnut frame with 3/4" glass siliconed on the inside to it. I built a plywood trickle filter that is 4' high by 2' wide by 4' long that has about 3500 gals/hr flowing through it.

Is it a perch only tank, or are there any other species that are not being affected?

I had 1 small mouth out of 4 in the same tank that appeared to die from the same afflication while the other 3 no issues so far.

Water changes are often a good catch-all solution when you don't know what's going on. Even if the water quality is good, if you have a parasite or bacterial infection that you haven't identified water changes can knock down the pathogen numbers to something more manageable by the fish's immune system. I've gone to 50% daily water changes when I see significant losses with no obvious cause, and it has helped within a couple days (either that or the sick fish had all died by the point...). I would think it's worth a try, although that is a LOT of water on a tank that size.

How big is the window, and how did you decide how thick the glass needed to be? I had been thinking of building a plywood tank of about those dimensions one day, but still a few outstanding engineering questions. Double plywood was something I hadn't considered though. Is the paint the only thing you had to do to waterproof it? Also, how do you do water changes? Would it be worth building the tank elevated so you have a true bottom drain line, or is it more worth it to have the support of the floor on a flat bottom?

I like your logic for water changes. We have decent water rates in Winnipeg so a week straight of that or a little longer would not be so bad.

As for the tank, I've built a number of plywood tanks in the past with this one being the biggest. The plywood I laminated together with decent wood glue so in affect creating one piece of plywood that's an 1.5" thick which is incredibly strong. All the the joints are rabbit-jointed to gether, glued with polyurathane glue and screwed. Alot of people who build these things talk about doing more in trying to add more for water-proofing the wood. If the intial paint does not stop the water, you're still going to have to empty it. So, what I do is ensure that won't happen. Particularly in a tank this size, I did 5 thick layers of paint. These tanks are incredibly strong if they are built right but if they have a weekness it is damaging the finish with decorations in the tank, particularly large rocks.

I have no magic formula for thickness of glass, obviously the higher you go the thicker it has to be. I had built a 500 gal. in the past (10'X24"X3') in the past with a 1/2" thick piece with no noticeable bowing. This one I used 3/4" (32" high). The frame is only 3 inches wide with glass only overlapping by about an 1" on the inside of the aquarium. It is also only held on by silicone and water pressure. When initialy filled, this is where it might leak, empty and apply mor silicone! This tank has 4 wooden (fur) braces across the top with threaded rod inbedded in them going front to back. With these braces I see no bow in the back of the tank.

The tank sits on a stand that is 18" of the ground. It uses 3 rows of 6"X6" fence posts(15 total), tied together with 2"X10"s. The top of the stand has a layer of 3/4" plywood on it as well. I had to spend alot of time on this to get it flat and level since it sits on a basement floor.

I would not recomend putting a drain in the bottom of the tank as there would be alot of water preasure on it. I have 4 2" drains as high up on the back corner side as I could make them for the filter which works well.

In the past I have built an automatic water changer but have not employed that with this one yet. Just using garden hoses for the moment.

I don't know how familiar you are with trickle filters, I've done something a little different with this one. I added a second pump to it that pumps water back up to the top of the filter. The return line of this pump has a number of T's with ball valves attached so I can pump water out of the filter during a water change as the main pump is turned off at that point. When I do an automatic water changer, it will be done from the sump of this filter.

If there is couple of important tidbits that I've learned the hard way about building these tanks is where water will have "frequent" contact with the wood, apply whatever water proof paint you are using to it, and, round any sharp edes where you are going to apply the paint to.