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Acclimation vs. adaptation

Posted By: tom b w <waltzek@neuro.fsu.edu>
Date: Friday, 18 September 1998, at 11:35 p.m.

Thought I'd bring up a topic a little off the loach subject but still related to keeping tropical fishes. Have you ever heard of hardwater discus, angelfish, neons, cardinals, etc? If you have I'd like to stimulate the following thought. These fishes, as many of you will already know occur in the amazon, mostly in very soft acidic pure waters (e.g. rio negro). So from my point of view it seems highly unlikely that breeders of these fishes have in fact produced strains that either tolerate hard water better than soft water or actually require hard water (versus simply tolerating hard water). Now I bet none of the companies make either of the two above mentioned claims but I've talked to people who have made these claims. My point is that these fish may be acclimated to hard water but adapted to hard water is a totally different thing. Proving adaptation is an extremely diffucult thing and I would be astounded to hear of tropical fish farmers or the like going to the extraordinary lengths it takes to prove this and publish their findings. This assumes that the necessary mutation (mutation for tolerating hard water) could and does exist somewhere in the discus breeding program gene pool. O.K. at this point you may be saying, "Well I don't care if they are adapted or acclimated, I'm only interested in whether they tolerate hard water." However, if they are making claims that there fish will easily tolerate water conditions that interest you do to your local conditions than I would point out that many wholesalers keep there fish in Thought I'd bring up a topic a little off the loach subject but still related to keeping tropical fishes. Have you ever heard of hardwater discus, angelfish, neons, cardinals, etc? If you have I'd like to stimulate the following thought. These fishes, as many of you will already know occur in the amazon, mostly in very soft acidic pure waters (e.g. rio negro). So from my point of view it seems highly unlikely that breeders of these fishes have in fact produced strains that either tolerate hard water better than soft water or actually require hard water (versus simply tolerating hard water). Now I bet none of the companies make either of the two above mentioned claims but I've talked to people who have made these claims. My point is that these fish may be acclimated to hard water but adapted to hard water is a totally different thing. Proving adaptation is an extremely difficult thing and I would be astounded to hear of tropical fish farmers or the like going to the extraordinary lengths it takes to prove this and publish their findings. This assumes that the necessary mutation (mutation for tolerating hard water) could and does exist somewhere in the discus breeding program gene pool. O.K. at this point you may be saying, "Well I don't care if they are adapted or acclimated, I'm only interested in whether they tolerate hard water." However, if they are making claims that there fish will easily tolerate water conditions that interest you do to your local conditions than I would point out that many wholesalers keep there fish in whatever water comes out of the tap (in many cases hard alkaline water). So are wholesalers producing hard water discuss strains also? You guessed it they are producing hard water acclimated discus. My final point is that you cannot easily change the physiological attributes of any organism that evolution has worked to produce. Remember phenotypic plasticity (the ability of an organism to change with differing env. conditions=sort of equates to acclimation), well this is a true biol. phenomenon but it does have limits. I'd be willing to bet the house that if you did the experiment than the data would reveal acclimation and not adaptation. Use two 55 gal. each with a breeding pair of discus from the same stock (1 pair from hard water tolerant stock and other pair from normal non-tolerant). Place both pairs in the same hard water and see if they'll breed (I have read good accounts that say that discuss will breed in hard water). If they do, compare growth, color, offspring number, etc several generations. I bet there would be little to know difference from the start or after the first generation in these parameters. So how are these fish better adapted or better suited to aquarium life? The one arguement that might be brought up is there ability to acclimate to hard water easier in the beginning than a fish never exposed to such conditions-Tom
 

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