I don't think it's possible to say an exact number. Here are several articles about hillstreams http://www.loaches.com/articles & oxygenation in loach keeping
What I find really interesting is that they will spawn in a tank with nothing more than an air-driven sponge filter. The fry are then raised in the same tank.
the link is not working. i had trouble earlier today getting around on loaches.com so i think they are just having technical problems right now. ill check the link again in a day or two.
i found this site that has a chart that maps out the ppm maximum that water can allow according to the temperature and salinity. i know its freshwater so salinity is 0. but the chart still helps.
What I find really interesting is that they will spawn in a tank with nothing more than an air-driven sponge filter. The fry are then raised in the same tank.
that is interesting. maybe they dont spawn in the strong current of the "fast flowing rivers" all the articles talk about. maybe they find calm shallows during breeding season. thanks for the info!