Because Uruguay is located toward the southern end of South America, as opposed to being strickly tropical, it is more temperate.
This means the fish species have evolved to live in changing seasons. There is an actual winter there, it snows, gets cold, sort of like a winter in the state of Georgia.
So the Uruguayan cichlids and other fish have evolved to experience a cool down. How drastic this cool down needs to be, might be determinant on whether they are from northern or southern part of Uruguay, and example might be Gymnogeophagus balzani, that come from more northern areas, and doesn't need quite the cool down that other more southern Gymnos appreciate.
Before i became aware of the season there, and when I tried to keep them at constant tropical temps, they didn't do so well, ( being prone to certain fungus diseases).
Once I realized the reality and gave them cool downs they did much better, colors brightened, and certain maladies ceased to be a problem.
I found keeping a tank at room temp (without a heater )worked well.
Below Australoheros fry.

Gymnogeophagus quilero below

Beside cichlids, there are tetras from that area (ex Buenos Aires tetras, and cool water piranha types) Plecos, and more.
There are other MFK members with plenty of experience, and that have traveled to Uruguay to collect fish, Ken Davis, and Matt Quinn to name a couple, and
I suggest you visit aqvaterra on FB for more info