His problem was that his guppies were very consistently dying. He had no idea why. The more we talked, the more confused I became. So frustrated had I become that I asked if he would accept a house call (kind of a fun reversal for a physician.) My classes for the following day were all set up and (remarkably) the papers were graded. I promised to make the hour run up the toll road and be at his place in Skokie by 7 something PM.
When I arrived, he pulled out one of the better tropical fish encyclopedias. He skimmed some of the creatures he was curious about. "Yep bred that" "Yep, lost those."
He asked if I would like to see his medical photos. Wasn't thinking about his specialty - pathology or the study of what causes diseases. Well I got treated to some of the most impressive photos of cancerous lungs and throats I had ever seen. In fact there was more than I really cared to peruse, but fortunately dinner was long before.
When he showed me his eight or ten 10 gallon tanks, I was treated to a vision of bare bottomed tanks with box filters, some flake food on the bottom and a dead and dying guppy (among the living adults and fry) in almost every tank. Despite the messy tanks, I was stumped as to why every tank looked so much the same.
At the time there was a top-notch shop - AquaMarines - about 20 minutes away near the NW corner of Chicago. The proprietor had a pretty good (dissecting?) microscope and had been taking fish pathology courses from George Bassleer at Shedd Aquarium. In desperation I called him and he (a night owl anyway) most graciously agreed to stay open and check out the guppies. He asked for a water sample, a dead guppy and a dying guppy.
I really felt bad about dragging that retired gentleman, in his 70s, out into sub-zero weather, but he too was quite willing to get to the bottom of those mystery deaths. We got to the shop about 9 PM.
Jerry, the shop proprietor, measured the water for organics (ammonia, nitrates) and it seemed ok. He killed the dying fish as quickly and painlessly as possible and opened both guppies we had brought along.
Jerry was really puzzled in that he found no internal parasites. Nothing externally either.
He did notice that the spleen and the liver were dramatically wrong in size. One was shrunken. (Don't ask me what a shrunken or swollen fish spleen or liver looks like.) While one had shrunk, the other had ballooned way up in size.
Guessing that those two organs were not only a part of the digestive system, but also the "osmoregulatory system" he went back to the remainder of the water sample.
Chicago (Lake Michigan) tap water has a hardness of about 155-160 PPM. The water from the fish tanks was 400 PPM! That is something along
the line of some of the very mineral filled Rift Lakes! He didn't even bother with TDS (total dissolved solids).
He mentioned his results and a little bulb clicked on in both our minds.
"When the water in your guppy tanks evaporates, what do you do?"
"Well.... I top it off with tap water."
That was it! The guppies were exhausting themselves trying to get the extra minerals out of their systems.
Freshwater fish constantly have to deal with the water around them seeping into their bodies. They cope with that by almost constantly passing very dilute urine (mostly through their gills). This enables them to hold on to essential minerals.
Marine fish, by the way, have to keep the water in their system from passing through the semi-permeable barrier of their skin into the sea. They do that by drinking lots of water and passing a small amount of very concentrated urine. This way they keep the H2O and get rid of the extra minerals.
Well these guys were having to do the salt-water thing in a freshwater tank. In cases of illness, fish sometimes die in the reverse pecking order of their tank. That seemed to be what was happening.
.....
When I had the privilege of stopping by the Lockwood's a little while back, I noticed Scott quickly grabbing a bucket and pouring water into several tanks.
"R.O. water?"
He smiled.
That's the only way to top off a tank in the winter and not fossilize one's fish. The "40" gallon tank in our living room with the powerhead needs about 7 gallons of water a week. So many plants grow out of it and drop leaves that it is losing some mineral and waste material that way. But I would have pickled those rainbowfish years ago, water changes not withstanding, without the demineralized water.
For those without such a toy as an R.O. unit, you need to cover the tank to minimize evaporation. (Catching rain, even if it was clean, isn't much of an option in January.)
Aim powerheads across the tank and not up. Cover power filter tops. Do run the sponge or corner filters at a pace which generates just a modest stream of bubbles. (Biological filters run more effectively if there is a little "surface time" with the filter media anyway.)
You really need to do more or larger water changes because everyone's tank will increase some in terms of hardness. The more frequent water changes will limit this to some degree.
But for those who don't consider what winter evaporation does, they will have to ponder some more "winter time mystery deaths". :(
For a little more on osmoregulation:
http://groups.msn.com/Breedingtropicalfish/osmoregulation.msnw
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