Velvet

[whuntley]

KL,

Forgive me, but I must disagree, partially, about the ubiquity of Velvet. The beasty goes through a cycle that includes a free-swimming stage. In that stage, the flagellate must find a host within 24 hours or it dies,

Before becoming free-swimming, a cyst falls off, rests and divides on the substrate, the time being fairly short if temperature is moderately high (28-30C). I'm not sure how long this takes, but it is hours or days, not weeks.

A warm week without fish virtually assures a tank with no Velvet organisms. They seem to be everywhere, because the fish you then add to that tank often carry invisible infections with the parasites only on the gills. They start the cycle over. Healthy, unstressed fish can carry and keep a Velvet cycle going for years without symptoms.

Symptoms then appear when a stressed fish gets an external (skin) outbreak, or a whole batch of babies mysteriously dies. The latter require exam under a microscope to be sure it was Velvet, but my experience is that about 90% of my sudden mass baby deaths were due to this one disease.

Fish from commercial channels often have been selectively bred for some resistance to Velvet, so they very often act as carriers. A quarantine in salty water may not be a bad idea, for fish from the local store.

There are more and less virulent forms of Velvet. Salt and acriflavin do a nice job on the common, slower-developing kind. I had one outbreak so virulent that it took drastic isolation techniques to keep it from wiping out my fishroom (150 tanks, at that time). I lost the original Nothos where it first appeared, and several other species before it was whipped. I would almost swear it came in with the peat and eggs of those fish, sort of like glugea outbreaks do. As I recall, only antihelmenthics really cured it, and they had to be applied quickly. [It was some years ago, and I forget which one I used. Sorry.]

This outbreak was the only one I have had that clearly survived without an obvious host. I can ony assume it was attached to some of the eggs, and they took the place of the usual fish host.

Bottom line is that you can only break the cycle by leaving a tank without any hosts for a week or two, or you can add salt at about a tablespoon per 20L to water that is not too soft to start with. [If all you have is very soft water, you may need to harden it with some "Equilibrium" o/e to keep the salt from being toxic.]

Wright

[retro_gk]

Just lost 16 L. tanganicus juvies to what looks like velvet overnight ...hope it doesn't spread to any of the other fry tanks...

[timebomb]

You're probably right as usual, Wright but my experiences with Velvet (which are many ) have led me to believe the cysts of the parasite can remain in a dormant state. I've seen Nothos infected with the disease when nothing new was added to the tank, other than peat in a breeding bowl. It could also be Tubifex worms and Daphnia are capable of hosting the parasite but I have no evidence to prove this, other than speaking from experiences.

I've often wondered too, given that they are so highly susceptible, how doNothos deal with Velvet in their natural habitats. Wouldn't an outbreak in one of their ponds wipe out all the fish?

Or is it such that no matter how widespread the infection, some of the Nothos will survive the disease? I say this because just recently, I had an outbreak of Ich in my main tank where I have many Aphyosemion australes. For various reasons, I didn't do anything to eradicate the parasite. Anyway, among the 30 or so, 4 somehow or other managed to survive the disease. There were no signs of infection on their bodies and they are still swimming happily in the tank.

Loh K L

[hobbit6003]

Well KL,

The most under-rated mechanism that the fish has to help fight disease, is probably its own immunity system.

Like I've mentioned before, in the wild, there's presence of oodinium parasites too, but because of the sheer volume of water, the pathogenic concentration of these parasites are therefore much lower than what we have in small confined space and volume of water that our tank houses. Thus, an outbreak in the wild would be less likely, although the weaker fishes do succumb.

Secondly, fishes living in their natural habitat, if left undisturbed, will not be subjected to as much as physiological stress that our aquarium fishes have to deal with. Stressors like overcrowding, waste build up, wrong water condition, peer aggression, etc, will make the fish much weaker immunologically, and when this make them much more susceptible to pathogens than their wild counterparts. Together with small quarters and overcrowding, this will then propagate an outbreak in the tank when the pathogenic concentration increases to an epidemic level.

As you also have observed in your Aphyosemion community, some fishes managed to heal despite you not doing anything. That's because in these lucky fishes, they were probably not that badly infected, and they were probably very healthy before the outbreak, and their immunity system kicked in and managed to rid themselves of these parasites. This is what we called Acquired Immunity, that exposure to these pathogens allows the body to develop a resistance to them, like a antigen-antibody type of reaction. In the wild, this happens too, and because of factors as above, the survival rate would be much higher than what you've experienced.

You see, like what I've mentioned a few posts earlier, there's no one single determinant as to the virulence of the pathogen and the prognosis to the various diseases, there are many factors which operates inter-dependently.

And yes, the spores and cysts of many parasites and bacteria, can stay dormant in unfavourable condition, and will proliferate only when condition favours them. Hence, most of these infection or infestations, are termed as an opportunistic disease.

Cheers,

Kenny

[keehoe]

In other words, healthy fish is still the most important defence again all these disease.

[whuntley]

OK.

Time to go do some water changes, again.

I'd bet that those folks who have built automatic or continuous water change systems into their fishrooms (Barry Cooper and Lee Harper come to mind) will never see outbreaks of such opportunistic parasites.

It is amazing that the hobbyist does much better with Nothos in quite hard water, with some added salt. The natural habitats, according to measurements reported by Prof. Brian Watters, tend to be mostly quite soft water!

Wright

[markc]

I have to agree with Kenny regarding "opportunistic parasites" and pest i must add. My EXO tank is infested with Hydra again. What surprise me the most is. I didn't added any plants/ fish into the tank at all. The only difference between this thank as oppose to others is i feed them BBS every now and then. And the fishes is not very active eater.

It could have come from the tubiflex and the population expanded by feeding BBS. Going to get another plasic hotel for the fish while work on the "solution". I am having a shrimp tank next to it.....

Maybe that explain why my EXO not spawning.

So Tubiflex + BBS = higher chance of getting Hydra.

[timebomb]

Mark,

The Hydra can't possibly come with the brine shrimps. What is more likely, they were already there in your tank in small numbers but you didn't know they were there. With baby brine shrimps around, the Hydra multiplies rapidly and that's when you start to notice them.

Kenny,

Thanks for the detailed explanation. Just one more question - what is it about fish that makes some species highly susceptible to certain diseases? In the same tank where almost all my A. australes were infected with Ich, the lone Notho guentheri which was really old, skinny and weak didn't show any signs of white spots on its body. Besides "acquired immunity", there must also be "inherited immunity". Right?

Loh K L

[hobbit6003]

Hi Kwek Leong,

Haha, it is not exactly 'inherited' immunity, but besides acquired immunity, there's this thing called the natural immunity. This are made up cells like the lymphocytes and macrophages, whereas acquired immunity is brought about by immunoglobulins (Igs). Acquired immunity is more specific, whereas natural immunity is not pathogen specific.

In the case of your old nothos, however, i don't think that it is due to natural immunity, although you can never be sure. I'd think that it may have acquired it sometime in its life.

Besides fishes having immunity against a certain type of organisms, some organisms are also host selective or specific.

All the above would probably help explain why certain fishes are more suceptible to certain diseases.

Cheers,

Kenny

[markc]

Hk Loh, I think the Hydra came from the tubiflex i bought from fish shop. Like what you have mention. Came in small quantity but multiply quickly as in the present of baby brine shrimp. Because everything in the tank was brand new.
Except the Java moss. Which is from my old tank with no sign of Hydra despite feeding of BBS.

For disease/ parasite to attach to living creature. Some form of genetic interaction is required. Some creature is genetically matches the requirement of the parasite and hence an target to the parasite looking for home. With this interaction, the parasite "deform" into the next phase of its life cycle and with the presence of host(s), they multiply.

Some parasite have multiple choice of host, human, fish, snail, pig etc.
So the first criteria of being a host is genetically suitable for the particular strain of parasite/ bacteria.

Like all living creature single strain of parasite/ bacteria born with slight different capbability. Strengh, ability to withstand a particular drug, ability to infect a particular host, being lucky to find a host.. etc etc

These can be breed selectively by giving them the living environment that only they can survive. That capability carry on to the next generation and so on.