"maria" wrote in message
oups.com...
It seems that every corycat I get eventually succumbs to the same
disease. The only symptom is that the fish loses its balance and cannot
swim or lie on the gravel straight. Eventully the fish dies. All my
water parameters are good, the temperature is 78F and I keep 2
angelfish, a pleco, some tetras and ottos which are all doing very
well. I really like cory cats and I want to have them in the future but
I have to figure out what is going wrong. Thanks for any help.

Hi Maria;
I hope I can help you and your fish. I don't know your experience level, so
please bear with me...

It would help if you gave a little more information, like what size
aquarium, and exactly how many of each species you have. You say your water
parameters are good, so I'm assuming that crowding or overfeeding aren't
part of the problem.

This sounds like the symptoms of an internal infection commonly called
"Whirling disease", caused Myxobolus sp. and a few other bacteria. The bad
news is that once a fish has symptoms, it's usually too late to cure. The
good news is that you can take steps to prevent it.

Corydoras catfish spend most of their time on the bottom of the tank, and
their barbels (whiskers) can easily get cut on sharp rocks or glass pieces,
if there are any in the tank. Infection from these injuries can easily
spread to other parts of the body. You didn't mention any symptoms of this,
but it's best to make sure.

Frequent partial water changes lower the amount of nitrates and decaying
organic matter in the tank, also reducing the amount of bacteria present.
Opinions vary, but 10 percent per month to 20 percent per day are commonly
recommended. On my own tanks, I change 20 percent of the water once a week

Treating the tank with tetracycline will also greatly reduce the amount of
bacteria present, but can kill off the nitrogen cycle bacteria. Be sure to
do frequent partial water changes after treating the tank according to
directions on the package. I would treat the tank with antibiotics starting
2 days before you add your next group of cories.

When putting new fish in the tank, pour the fish bag into a bucket with an
equal amount of water from your aquarium, and let them adapt to it for about
15 minutes. This will reduce the impact of any temperature or pH shock. When
the time is up, net them out, and put them into the tank. Next dump out the
water in the bucket, rinse it, and add treeated tap water to top off your
aquarium. This will greatly reduce the amount of bacteria from the store
tank that enters your tank. When you move them to the aquarium, fish may get
tangled in the net, but it's best to let them free themselves. Touching fish
with your fingers removes their protective slime coat and makes them more
vulnerable to infections.

One other observation: your ottos and smaller tetras may be in danger when
your angelfish reach adult size. Many adult angelfish will eat any small
fish they can catch.

Wishing your fish well;
Limnophile