Coldwater Suction, The Hillstream Loach and Dissolved Oxygen.
Updated: Nov 14, 2021
The fish of the family Balitoridae are the known as the hillstream loaches and are native to east and southeast Asia. The little guy pictured above is of the genus Sewellia; which is very popular in the aquarium trade. Their modified pectoral (front bottom) and pelvic (middle bottom) fins allow them to suction onto rocks in fast moving streams.
The streams which these fish inhabit are cool in temperature and and have high flow. These streams originate high in the mountains where the flow is rapid, and then begin to slow down as the degree of incline decreases. Eventually, the streams combine with other similar sized streams until they form a lowland river, which eventually empties into a lake or ocean.
The hillstream loach is adapted for higher dissolved oxygen content due to the colder water retaining higher levels of dissolved oxygen as compared to warmer water. If you decide to house hillstream loaches in your aquarium, make sure they have plenty of flow, cooler water, and lots of plant matter to consume.
There are other ways to achieve more dissolved oxygen in your aquarium other than cooler water. Most people think adding an air bubbler will increase their oxygen content, and it will, but not in the way you think.
The air bubbles form the bubbler are too large to be considered dissolved, but what they will do is agitate the surface of the water, and that's where gas exchange happens. When the surface of the water is agitated, carbon dioxide, nitrogen, and oxygen gas transfer between the water and the atmosphere. Any method of surface agitation will work, such as a correctly pointed powerhead, or the outflow from your filter if it is near enough to the surface. Because nitrogen gas can mix into the water as well, over agitating a saltwater tank can add too much nitrogen to the water and cause the rapid expansion of excess nitrogen in the fishes' bloodstream. In human scuba divers, this is known as nitrogen narcosis.
So consider the hillstream loach for your cold-water aquarium, and just as with any species, make sure you recreate their ideal environment.