I have a loach, clown to be exact, that is maybe nine years old and about 9 or ten inches long. Also Ron Leftwitch has one that he showed at the last Aquafest that was even larger, a real monster.
I do recall that someone had pictures of a spawn 20 years ago in a very large aquarium with lots of large plants. The clowns were not visible most of the time as they were in the roots of the plants. There were no other fish in the tank. And as i recall there were only about 6 adults. There was at some time an indication that one of the sexes of clowns has a greenish color.
Maybe I will look it up, but don't clowns in the wild average 15 to 18 inches. Maybe they need to get to this size to spawn.
BTW one of my other clown loaches has a large circular spot on the side in place of the black stripe. It is only on one side.