I don't yet have any personal experience with these, but thought I'd chip in what I've read eslewhere ... they like highly oxegenated water, with temps somewhat on the lower side - which makes sense, when you consider the "Hillstream" part of their name, which presumably describes their natural habitat. Probably like a lot of hardscape (smooth rocks, and/or minimally-planted wood). Very efficient algae eaters.
I have one of these little guys - I have a 30 gallon x-high tank. I have DIY CO2 and a Aquaclear 50 filtration. He/she seems quite happy - save that it is territorial - It chases both of my Oto cats whenever it gets a visual lock. No harm done - eventually the cat get out of it's visual range. I have tossed in algae wafers and a few blanched peas with no interest. If you get one, make sure you have enough algae because it's picky :)
I have a Reticulated Hillstream Loach, and I have trouble convincing people that it is not a Plecostomus. They do have a similar appearance and similar behavior, but these fish are definitely their own thing. I only have one of these in a 36 gallon community tank, but that is only because I have not been able to find more in any of the stores in my area. These fish like lots of water movement, so be sure that your filter turns your water over enough times per hour to keep a nice current going and to keep the water sufficiently oxygenated. Most of the material I have read about these species (and there is not too much of that...) indicates that they are difficult to keep, but my experience with the single specimen in my tank has been very easy. It is important that you supplement their diet with algae wafers or something similar if you do not have enough algae growth in your tank to support their needs, which most tanks will not be able to to for long anyway. My particular specimen is not at all shy, and can almost always bee seen in a conspicuous spot in the tank. None of the other tank inhabitants bother this fish, and he seems to keep to himself, which would make one or more of these striking fish a good addition to a tank where the hobbyist wants something exotic but not exceptionally hard to keep.
I have one of these in my 125g discus/planted tank. I was concerned that 86 degrees f was going to be to hot, but once I add a stream of bubbles he stopped gasping. He has been in there for 2 months now and loves it. Eating really well and the 2 plecos don't bother it. My wife calls in the "flowder fish" I have given up correcting her(:
The previous comment is correct: the image on the right is Beaufortia kweichowensis. I have had one for nearly 4 years (I originally purchased 2, but one died 2 weeks after I bought them). They do indeed need increased oxygen. All I had to do was lower the water level half an inch and the filter I have hanging on the back now tumbles in more like a miniature waterfall, which creates more turbulence and hence increases oxygen level. So even though the tank gets to 80 F sometimes, this guy continues to do well (it likes to hang out with my L128-Blue phantom pleco). Not a spot of algae in this tank between those two. They are frequently fed algae tabs and broccoli or peas, sometimes green beans.
May chase after similar-looking fish like otocinclus, but it won't hurt them. It kind of just flops on top of them a few times until they dart away, then it goes back to just scooting around. Needs to have nori or veggies for when it runs out of algae and also needs either cool water or high flow, or both. They like highly oxygenated water, being from literal hillstreams, but should be alright if it's just a large patch of fast water instead of the entire tank. Just be sure they have some room to move around.
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