What you describe with the cardinals is not unusual. It is my opinion that you
should not replace lost members of a group of cardinals (this applies to many
other species as well). Rather you should buy your group and try for the best
result you can get and stick with that. The problem is that if you buy a dozen
and that dozen includes two unhealthy ones which die after two days, and you
replace them, the person at the LFS is likely to catch you the slowest
(easiest to catch) two in the tank. You put them in with the relatively
healthy fish which are being exposed again to unhealthy members of their
species. Each time you do this you are risking the health of the population
and likely prolonging your problems.
Of course if you get good healthy cardinals and treat them well you shouldn't
have any problems.
Unless the fish are caught and bagged roughly. Inexperienced or calloused fish
baggers can damage cardinals in handling quite easily, then the fish will
succumb to bacterial infections some time within the ensuing 48 hours. If the
infection spreads some individuals will be dying a week later. Often this is a
blood infection (septicemia) and no external signs are visible but the onset
of the condition is quite rapid once the immune system has been overwhelmed;
that's similar to the way we react to blood poisoning. Under the microscope
you can see bacteria in the blood of the fish. Fish in the early stages of
such an infection might seem normal until they are stressed by being caught
and moved.
Then of course there are the tankmates, and even though the ones you
mentioned are all "community" type fish they would ALL be quite eager to
harrass new cardinals which have not gotten their berrings yet in a new tank.
The resulting little bumps and bites are more opportunities for bacterial
infections. Then if the fish are further stressed by the nitrates, temporary
low oxygen levels, pH change, hardness change, or simply excess organic
material in the tank, the bacteria will get the upper hand. There are bacteria
everywhere of course, cardinals just aren't very resistant to alot of the ones
they encounter. Your freind might even have a resident population of some
nasty bacterial species. Maybe it came in on a dead betta. Rarely you can get
a slow-growing columnaris infection on the skin of some fish that is enough to
kill them even though no damage is evident. New bettas often carry lots of
columnaris bacteria.
There are other possibilities as well:
- Toxins of some sort in the tank. Even though the other fish seem healthy
cardinals are more sensitive to chemical toxins than most other fish. I use
cardinals as test fish (canaries) when trying to decide if there is something
wrong with a water supply.
- Some type of shock. You asked if cardinals can die directly from stress and
the answer would be that they could die from shock and they are one of the
species that can go into shock simply by being transported, especially if
there is some additional ailment.
- Previous exposure to extremely bad water or overdose of medications. There
are several things that can cause long-term damage to these fish (their gills,
kidney, and liver) and make them prone to falling to something else or unable
to tolerate future stresses.
- Bad food, now or in the past. Stale or moldy food can cause liver damage
which will cause a fish to become sick at a later date when exposed to what
seem to be mild stressors. As an example, I've found bad containers of freeze
dried foods on numerous occassion but only once have I ever heard someone else
complain about finding such a thing. Do I just have bad luck? I don't think
so. The same applies to frozen foods, and you know that flakes are no good
after a while.
- Gill parasites. I don't think that's it because you should notice some signs
of distress before the fish die. Still, it's easy to miss things on cardinals,
behavior-wise, and their gills always do seem a little red and it's hard to
tell if they are breathing faster than they should.
-A combination of things. Duh.
-Something that you thought you checked and discounted. We miss things.
Having said all this I realize that it will be of no help to your freind. She
simply has to get to a point where she is no longer adding cardinals to her
tank. Like you said, she doesn't have a quarantine tank so I don't think she
wants to get into medicating and risk damaging the healthy fish she has. When
and if she has some cardinals that are adapted to her tank then she can stop
and enjoy them. If she never gets to that point then she can wonder with the
rest of us why cardinals didn't work out in her tank, but nature is often
mysterious and recipes for what goes with what under what conditions don't
always work out like it says in the books. If she needs encouragement tell her
what I said, that this is not unusual, and that it is possible that she got
some "bad" cardinals even if the LFS did their best. These things happen and
it isn't easy to get good healthy cardinals.
I probably missed something, but I have to stop typing now.
Steev
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