Kuhli loaches are the honest exception
A young kuhli loach cannot be sexed by any method a home keeper can use, and this article will not pretend otherwise. Unlike guppies with their telltale fins or plecos with their bristles, kuhlis of both sexes wear the same eel-like striped body, the same tiny downward mouth with its whiskery barbels, and the same habits. Sellers cannot sex them, most breeders cannot sex them, and the fish are almost never bred in home tanks partly for that reason. If a shop assistant confidently labels your young kuhli male or female, you are hearing a guess dressed as knowledge.
The one clue: a mature female full of eggs
The single kuhli sign that means anything appears only in a well-grown adult female carrying eggs. She thickens noticeably through the front half of the body, and the eggs inside can tint the underside of her belly a pale green, visible when she drapes herself over a plant or climbs the glass, which kuhlis do more often than their bottom-dweller reputation suggests. Outside that state she subsides to the same ribbon shape as every other kuhli. A young loach, slim and still growing, offers neither the thickness nor the tint, so the clue belongs to a later year of the fish's life.
Claims you will read, weighed honestly
Guides sometimes suggest that male kuhli loaches have larger, thicker pectoral fins, or that females are simply the bigger fish. Examined closely, these claims collapse: the fin difference, if present at all, is too slight to judge on a wriggling fish a few centimetres long, and size in a young group reflects feeding order and age far more than sex. Kuhlis also pile together in tangled heaps under wood and leaves, making sustained study of one individual genuinely difficult. Weigh any source claiming easy kuhli sexing accordingly, and spend your effort on the group's comfort instead.
Why the unknown rarely matters for kuhlis
Kuhli loaches are peaceful in any mixture, so not knowing the sexes costs a keeper nothing in daily care. Males do not fight, females need no separate provision, and the group should simply be kept at a comfortable size on soft sand with hiding places, since kuhlis are social and a lone fish hides constantly. Sex would matter only to a specialist attempting the rare home breeding of this species, and even those keepers typically maintain a large group and let probability supply both sexes. Your young kuhli's unknown status is therefore a fact to accept, not a problem to solve.
Noting the uncertainty, then any later reveal
There is value in writing down what you do not know, so a future owner or helper does not inherit a confident error. Record your kuhli group as unsexed youngsters, with their purchase batch and approximate sizes, and update the note only if a thickened, green-bellied adult ever gives the game away during a glass-climbing moment. Keeping that honest note in each loach's KinsLe Pet Passport means the record travels with the fish, uncertainty and all, instead of hardening into a wrong label nobody questions.