Should I try to match as closely as possible the same conditions that exist in the fishes natural range? It is a common question with good arguments on
both sides of the debate and all sides arguing with good intention but what are the facts.
The intuitive answer is yes because those are the conditions that the fish has evolved in and to which it is best suited.
Some fish which are known as "bread and butter" species are the fish which have always been in the hobby and have been bred in captivity for possibly thousands of generations. These fish have literally evolved to suit conditions found in captivity and not those which exist in the wild. But evolution doesn't happen so fast, does it? Changes can be brought about relatively quickly through selective breeding. It doesn't take long to create changes that give fish longer fins as we see in veil tail varieties or to bring about a colour changes in a species all through selective breeding.
With captive bred fish over many generations this same process of selective breeding has taken place but it has happened by accident rather than by design.
When the first wild caught fish arrived at the professional breeders facilities and placed in water which was quite foreign to them, many of the newly arrived fish would have died. Significantly a few would survive, this is because even within a particular species there are different levels of tolerances among individuals which means that some are simply more adaptable than others.
The ones which survived were simply more adaptable and it is these individuals which went on to breed. Over the generations these "adaptable genes" become fixed which means that almost all the population has them and new born fish have no trouble in living their lives in water that would kill most of their wild counterparts.
It goes further than this, if the species in question came from an extreme environment then the fish hich has been bred in more average conditions for many generations may well lose the ability to cope with those wild conditions. A good example of this is wild discus and captive bred discus.
Wild discus can be found where in some places the pH has been recorded below pH 4. To put one of these fish in captivity where the pH is slightly over pH 7 would do them no good at all and in all probability their lives would be shortened by it.
Captive bred discus on the other hand will have been born and raised in water with a pH of around 7 + or - 0.5 either way. The changes that allow them to do this have been bred in to them probably unwittingly over many generations as outlined above and if one of these fish, a blue diamond discus for example was placed in water with a pH of 4 or less it would quickly die from a condition known as acidosis, quite simply it has lost the ability to cope with those conditions.
Are of course completely different. They absolutely should be kept in conditions which approximate those found in the wild because those are where the fish evolved and what they are best suited to. This is one reason why wild caught fish have a reputation for being delicate. They aren't delicate it is just that they are being poorly housed in conditions which don't suit them even though other captive bred fish of the same species are thriving in the very same aquarium.
After everything written in this article it is still better to mimic the conditions found in the wild "a little" i.e try to keep discus in mildly acidic water or Tanganyikan fish in alkaline water (Tanganyikan fish are still commonly wild caught too) but avoid extremes.
Maintaining a pH of less than six or more than eight for the over whelming majority of captive bred fresh water fish is simply asking for trouble.