I'd have to agree that this type of thing happens, although I feel that
quarantine would reduce the occurrences.

However, I don't believe that this is the only cause. I think there are
probably quite a number of different causes.

One cause I have found that is closely related to the Netmax Theory involves
fungus.

The fish I catch from the Moore River all bring some kind of fungus with
them, although they are completely uninfected and totally healthy.

In the river, the flowing water must prevent the fungus from getting a hold
on anything. However, in a small aquarium, the tiny traces that come with
the fish eventually grow and cause real problems.

Everytime I add a new fish into the aquarium fresh from the river, there
will be a fungal outbreak unless I dose it with something first.

Jim


NetMax wrote in message
...
There is NTS (new tank syndrome) which is well known to almost everyone,
and there is OTS (old tank syndrome) which is known to most of the
regular readers here and experienced hobbyists, but I think I have a new
one for you to consider.

Have you heard of this scenario before? You introduce a seemingly
healthy fish to your tank (without quarantine, though I'm not certain how
effective quarantine would be in this case), and within a few days, all
the fish in the tank are dead (from bacteria and/or Ich). The common
denominator is that the hobbyist had not added anything to that tank for
a long time (over 8-9 months), and their fish were all healthy before.
This is a real heart-breaker, and to add insult, very often, the
introduced fish survives, seemingly oblivious to the carnage it has
caused.

Having heard of this occurrence from many other hobbyists (and
experienced it), I've a hypothesis which I'll call NGS (new germ
syndrome). I don't think it's as simple as the introduced fish being a
carrier. The problem is the prolonged inactivity of the immune systems
of fish which have been isolated for many months, preventing them from
reacting to the almost benign germs which are always present in normal
waterways. The human equivalent would be someone living in a sterile
bubble for a long time, who would be at a pneumonia risk from common cold
germs.

The problem is worse with fish, as they don't have an atmospheric shield
around them like humans. In nature, fish are all interconnected by
water, which is an easy conductor for parasites, bacteria etc. If one
fish is sick, they are all exposed to the same contagion, to varying
degrees of concentration, depending on their proximity to the greatest
source of the disease. Consequently, in nature, fish are always exposed
to disease, and the exposure typically ramps up (as the disease spreads).
This would require the fish (in nature) to have a very active immune
system in 2 regards. First, the constant exposure would require the
immune system to be constantly working. It would always be under some
attack, as diseases evolve to counter the fish's defences. Secondly,
since the attack is progressive, the health of the fish depends on the
immune system's ability to produce the correct defence for when/if the
disease concentrations become higher.

In an aquarium, with our relatively huge fish-loads, disease
concentrations ramp up faster than their immune systems can react. Also
the immune system's ability to defend against a particular contagion
depends on if it was ever exposed to that contagion before, so (in
theory) a variety of low-level exposures, successfully defended against
would produce the strongest immune system. However, by intent, aquarium
bio-topes do the opposite, reducing the attacking contagions to zero.

In an established tank, with no introductions for say, one year, you
might conclude that the inhabitant's immune systems are dormant from lack
of use. This might be ideal (as it indicates a contagion-sterile
environment), unless you want to add something (fish, plant, snail etc).
Then you have the worst case scenario, a new contagion, small
environment, and a bunch of immune-suppressed fish who will not even know
what hit them.

NGS, New Germ Syndrome

There are varying defences for this, but I thought I'd start by floating
the concept through the newsgroups for comment first. There probably
exists a more technical term for this (especially as applied to humans),
so if you know of one which applies to fish, please share it.

NetMax