Question:
I released 50 young Neon Tetras recently into my 27 gallon tank which
has been set over five years,
http://kobe.cool.ne.jp/kazkinai/main.htm
(one in the bottom)
And I'd been feeding them Tetramin 2 or 3 times a day. Fishes grew up
very fast and they became more than twice larger than I purchased in
just 3 weeks. However, in the last one week, some of the rather larger
fishes started to die and 15 out of 50 have already died so far. Does
over-feeding cause some sort of stress for fishes? Anyone has any clue
for that? All those fishes that have died had fat big abdomens. I have
been changing about 1/3 of water every two days so water was pretty
clean.
Answer:
It's probably because you added so many at once. The nitrifying bacteria had no
chance to take on such a huge bio load all at once.
New fish should be added a few at a time, over a week or two. This allows for
the bacteria colony to grow.
I'd compare your pH, gH and kH with where the fish came from. Mortality
at 2 weeks might be the result of a water parameter change which they had
been adjusting to (just my uneducated intuition). Or, you may have some
type of a bacterial infection, which at your fish-load, will make the
rounds very quickly. I'd cut the food back to what they can eat in 2
minutes, once a day, while researching diseases which more closely match
your symptoms.
You may be right. I'd been off my guard and quite free from caring the
bio filter because it has been set over five years. Before I add the
fishes, there were only a few full-grown, approximately five year old
Cherry barbs and I was only feeding them once in a few days because
they don't need much food. So I guess there weren't enough grown
bacteria and the excess of nitrite poisoned them. I reduce the feed
from now for a few weeks until the bacteria colony gets grown enough.
The pH is 7.0 and I had released them with mixing the water of tank
quite slowly into the bag fishes were in. But are there still some
stresses(pH shock or something) exist for fish if those pH, gH, kH
differ a lot from where the fish came from?
Infection is one of the suspicion I have considered, but some of them
almost dying rather looked like they are paralyzed by some poison, and
it seemed he can't control his body. So I convinced that the cause is
nitrite.
The symptoms do suggest possible pathogens (swollen stomachs), as many
things which would make them unhappy, would also cause them to stop
eating, but if it was quick, then there would be no obvious difference
caused by a lack of food.
IMO, cat's are not normally as bad a problem as some people might
imagine. Larger cichlids are not intimidated by them, and really small
fish might not even perceive them as a threat. The biggest problem that
I have found with cats, is to keep them from collapsing the canopy, when
they wander along the top trying to drink the water.
