You cannot compare this to tank bred individuals that have been bred to give several generations.
Yes and no. If breeders actively selected for fish that stayed healthy -- across a full 5 year life span -- and spawned freely at, say, the normal 25 degrees C, then yes, over time, you would produce a "domesticated" ram that was more tolerant than the wild type. However, if the fish used for breeding have short lives at lower temperatures, and breeding is done by raising the temperature, then this domestication process will not take place.
It helps to think of this in terms of genetics. To select those fish with genes that allow them to operate healthily across their normal live span at 25 degrees C requires that you maintain them for several years, and then breed from those fish that have clearly done well across that time frame. Say, adults who are two or three years old. This way you'd have a good handle on which fish had the tolerant genes and which ones did not.
But fish farmers and most breeders don't work this way. They breed fish as young as possible (which is why tank-bred fish are commonly smaller than wild fish, because females don't get to choose the biggest, strongest males) and routinely raise water temperature to trigger breeding. Ergo, they have no time (or inclination) to select cold-tolerant genes.
I would agree that over time angelfish and discus have both been "domesticated" to some degree, in part by hybridisation. None of the commercially bred angels or discus in the trade are true species. They're all hybrids, so as well as selection of favourable genes, there's some hybrid vigour in the mix as well, making these domesticated fish tougher than any of their parent species.
But I have seen no evidence whatsoever than ram cichlids are getting stronger over time. Quite the reverse in fact. Wild rams, kept in proper water conditions, are just as easy (or difficult!) to maintain as any other wild dwarf cichlid. Commercially farmed ram cichlids may be cheaper than wild fish, but are they easier to maintain? I don't really think so, not in any meaningful sense. Far too many people still end up with sickly rams that barely live a few months, let alone the 3-5 years you'd expect from a fish of this type.
Quite possibly ram cichlids will improve with time. Angels were first kept around 1910, and by the 1960s you had obviously domesticated angels such as marbled angels and golden angels. So there's been something like 100 years of breeding and selection going on. Perhaps if breeders made an effort to select ram cichlids with demonstrable tolerance for cooler water conditions, after a couple of decades we may get a genuinely hardy, fully domesticated ram cichlid. But we do not have such a fish now. At least, not in my opinion.
Cheers, Neale
Fishbase reports 22-26 C, but the usual 25 degrees C of most aquaria seems to suit them very well. At the lower end of the range, they'd be good companions for neons, swordtails, danios and other fish that don't like particularly warm water.
Cheers, Neale
Not to hijack the thread, but what are the temperatures of the rivers bolivian rams are found in?.