'Sheltering' our Fish

[aqua_chem]

A though occurred to me the other day on this topic.

In regards to pathogens: Do we shelter out fish? The more I think about it, the more I have to say yes. However, I feel that we are obligated to due to evolutionary circumstances.

Disease immunity has two major qualities: evolutionary and acquired. The later has already been discussed, but the other has been largely neglected. One only has to look at the case of sub-Saharan African populations and African trypanosomiasis, or "Sleeping Sickness," to see what I'm talking about. This disease is endemic to this area, and results in many casualties each year. Because of this, the populations of the area have adapted to increase the survival rates against this disease. One of the most well known adaptations is the prevelance of sickle cell anemia, which is found very commonly in this area. Both the carriers and the affected carry a resistance to the disease, and thus the gene is selected for. Imagine, if you will, that african trypanosomiasis established itself in the US. Many people would die, as they do not have evolutionary adaptations against the disease.


Now, take a look at your fish tank. More than likely, you will see fish from many different areas: central america, S. America, eastern and central Asia. Now imagine that these fish all brought in their native pathogens. Not a pretty site. This is why we must strive for sanitation in our tank: our fish have not even evolved to take on more lethal strains, much less the natural immunity.


As far as water quality goes, the exact quality of water varies widely around the world. Some water is cleaner, other is dirty. But if you once again look at the problem from an evolutionary standpoint, some fish have adapted for pristine water, or rather haven't adapted for nastier water, whereas other have. I think some common sunfish (bluegil I think) have an ammonia LC50 of near 100 ppm! However, when we bring these fish together in a tank, it is almost 100% sure that the water tolerance of all the fish is not the same. This is why we must maintain the quality: too clean water has never (that I'm aware of...) kill a fish, but you can't say the opposite is true.

 

[mfdrookie516]

Interesting thought. That's something I hadn't thought of (didn't even know about the human side of that discussion).

Now, take what you've just said and consider this.

You have a brand new tank, only use tap water with dechlor, do all the right things. You have fish native to your area only. How would those fish do in the wild after being kept 6 generations in a sealed ecosystem (your tank).


Would you say the same?

 

[aqua_chem]

If you allow the fry to be raised in a normal, non-sterile environment and therefore allowed to develop acquired immunity, I would say that they still would. Now, if we were talking hundreds of generations, probably not. It would all depend on the mechanism of immunity. Some adaptations, like simple protein alterations, would take longer as the negative side effects may not be enough to cause immediate evolutionary pressures. With trypanosomiasis, the adaptation comes with its own disease pathology (sickle cell anemia), so that immunity would be lost much quicker.


Six generations probably wouldn't be enough though.

 

[Ducky14523]

I dont beleive tanks are all that sterile. I house the bulk of my fish in container ponds through the summer, I know this is still different from a wild pond but the fish are still exposed to air born parhogens, contaminants, temperature fluctuations, leaf litter, disease carrying insects, etc. They always come back in for the winter much better for it, as far as i can tell. The fish in question are at most second generation being raised this way.