Gyrinocheilus aymonieri, the Indian Sucking-Loach

Gyrinocheilus aymonieri (Indian Sucking-Loach). This notorious fish is not a Loach— a Cobitid:— instead, it's a close relative that's been given its own family name: the Gyrinocheiliidae contain only this one genus, with four species. To sell you this fish, your LFS will label it an "Algae-eater," or more insidiously even a "Chinese Algae-eater," which may fool you, though just one time. Needless to say, this fish has not been seen in China, where Gyrinocheilus is represented in fact, but by a different species never seen on the market; instead it comes from northern India to Thailand. There is an albino variant at large on the market; the blonde isn't any better-behaved. Still, if you want a hefty scrappy loner that mumbles the cobbles in the swift current of your Asian hill-stream tank, this one's for you. As recently as 1992, the Indian Sucking-Loach was one of the twenty species most imported into the US.
 
Like most aquarists, I have had this imposter only by accident, because I didn't know the points to look for in recognizing the "good" Siamese Algae-eater, Crossocheilus siamensis (see just above). Sure enough, as it grew— under my very eyes— it lost its juvenile interest in algae, if it ever had any. Gyrinocheilus is really more of a toothless detritivore; it doesn't even have the teeth in its pharynx that real cyprinids all have. Before long, mine began ruthlessly chasing the other residents of its aquarium, just as everyone said it would. I couldn't catch it in its planted aquarium, but intestinal bloat carried it away long before it could reach its adult size— of just under a foot long, I hear.
 
There's not much that would recommend this fish in a community, but it does have a couple of curious evolutionary adaptation. Rather than lose scales from its belly in being buffeted against pebbles in its home currents, Gyrinocheilus has eliminated scales on its underside. More unusual, above the gill-flap there is a small opening through which water enters the divided gill-chamber, even while the fishes' sucker mouth is completely occupied with hanging on to an algae-covered cobble. In the rushing streams of north India, upper Burma and Thailand, where Gyrinocheilus makes its home, it's handy to be able to hang on, eat and breathe, all at the same time. So, while you're staring at that fish in the LFS, hoping it's not the dreaded Gyrinocheilus, remember, if it's hanging on to a stone by its mouth, you can be sure it's the Indian Sucking-Loach!
 
Not everyone would agree with me about this fishes' character. Kveeti defends G. aymonieri. "As far as the CAE goes, I have had several (well, 6) over the years, housed with various fish and only one has ever showed aggressive tendencies. To be happier, they need a territory they can call their own. If their only territory is an open tank without nooks and crannies, yes, they will chase."
 
Links. G. aymonieri at Wikipedia. G. aymonieri at FishBase (being called "Siamese Algae-Eater" alas).