Originally Posted by Herky
How about fish that have been raised in many successive generations in local water supplies over the course of many years? Is there any room for adaptation of locally grown species?
I ask because I purchased my discus from a breeder who has been producing fish in our local water, which is much harder and has a much higher pH than what it should be for discus, and has been doing so on a regular basis for nearly 20 years. Now, these fish are 1 town over, where the water conditions are much worse than where I live, and he produces lots of viable fish. My water is closer than his water to what it should be, but it's still not ideal. My water is generally around 7.1 straight out of the tap, but is very hard. In the town where he breeds them, the water is more on the order of 7.8-8.0. I don't know how he manages, but apparently he must be doing something like peat filtration or something to lower the pH if discus refuse to breed in high pH water conditions. As for hardness...everywhere where I live has extremely hard water...there's no way around it here if you want fish, you have to take the risk. I've had what I would consider luck with my discus and angels in water that isn't ideal, but I'm sure it's as byron mentioned...it's what we don't see that is the real root of the problems that will probably occur down the road. As far as adaptation goes, I suppose it's a matter of looking at millions of years of evolution in natural environments versus a relatively short time comparatively being bred in captivity...so the adaptability may be nil, or just a drop in the bucket. I really don't know. I guess what I'm saying is, if it is able to be determined that getting a fish from a local source that has fish that are potentially adapted to local water conditions...it may be beneficial to look into local breeders.
This is another good question on which there are differing opinions. And sometimes the particular species of fish also seems relevant.
Mikrogeophagus ramirezi (the common or blue ram) has now for many years been commercially raised; while wild-caught fish can be found in select stores or importers, most fish sold in stores are tank or pond raised fish. In spite of this, the fish remains especially sensitive to water conditions, never living long in water that is below 80F in temperature and slightly acidic and soft. I have come across several threads on this and other forums about aquarists' failures to maintain this fish beyond a few weeks, and in every case I can recall it is always due to the water parameters. In spite of being farmed, this fish has clearly retained its natural preferences.
There are fish like Pristella maxillaris, the Pristella Tetra. It occurs over wide-ranging water conditions in northern South America, even found in brackish water in some places. It is the only characin I personally know of that will tolerate brackish water; most characins are sensitive to salt. It is a species that seem capable of adapting to almost any type of water, and being healthy and reproductive.
I think the hardness may be of equal or perhaps even more importance that the pH. It is a fact that hard water causes blockage of the kidney tubes in cardinals. How many other "sensitive" acidic water fish may die from this or similar issues unknown to the aquarist?
I can't say that discus will not spawn in water outside their natural preference. I do have the views of Dr. Chris Andrews, director of the Steinhart Aquarium, that some fish seem capable of tolerating wide variances in pH, while others can't, perhaps due to something in their physiological makeup. He says he once maintained "healthy" discus in tanks with moderately hard water having a pH of 8, although he notes they did not spawn.
The whole issue may never be absolutely resolved until the time comes that we have scientific evidence of how fish metabolism and physiology works with respect to varying water parameters, and any variances between species. In the interim, the best approach to me seems to be one of providing the nearest thing we can to the fish's preferences, recognizing Dr. Andrews' opinion that we should neither take the "preferences" as absolute, nor should we completely disregard them. But along the way, understanding that we can't be certain of how this is really affecting each species, and some clearly show significant adverse health more than others.