As far as I know clown loach breeding rarely happens in aquariums. In fact, there is not one confirmed case of clown loach breeding in an aquarium. Even scientists who study the fish in the wild have not been able to demystify the clown loach's breeding behaviours. However, it is believed that the smaller (less than 8cm) clowns migrate up river to special breeding grounds. There are some people in the clown loach community that are trying to mimic the journey up river to the natural breeding grounds in their aquariums. Although, nobody has been successful yet, it is interesting to read about the experiments and I'm sure someone will make it happen sooner or later.
I think one of the biggest challenges in getting clown loaches to breed in an aquarium is that you have to exactly mimic the natural environment in the clown fish tank. Since no one really knows where the fish are when they breed, mimicing the environment is a lot of guess work at this point. Also, the clown loach feeding behaviours may change at breeding time, which is also something that researchers have not been able to shed any light on.
If I were going to try to mimic the cloud Loach's breeding environment I would first start with the journey up river. When a clown loach travels up river from a wide river into a small stream it's only logical that the strength of the current will increase. So, in my aquarium I would increase the water current a little bit every few days to try to mimic the clown's journey up stream. In nature, when the clown loaches travel up stream I think the food supply will change. And to trick the clowns into thinking they're really in a stream in Borneo or Sumatra I would have to feed them the right foods. Since I've never been to Borneo or Sumatra I really don't know what types of food are found in small streams there. So, for me it would be guesswork, but I think it's important to feed them right foods at this point.
As an aside, you may think that since they clowns never actually bred in nature they wouldn't know the difference. I beg to differ. Research has shown that if you have put aquarium bred fish into an aquarium with a fish who is their natural enemy the fish will be scared. Eventhough, they've seen their natural enemy in their lives they will be afraid. Many researchers believe that these sorts of things are passed on through genes. So, I believe that eventhough a clown loach has never breed, it knows when it's time and it knows/feels when the environment is right for breeding.
Another thing that will happen as the clown Loachess progress up river is that the water will become clearer. What I mean by that is in the large rivers that barely move the water is murky and When you move in the smaller stream the water flows more quickly and will be cleaner. So, what I might think about doing is making my aquarium a little murky. And then over the days as they increase the currents I also filter out the murkiness in the water to make it cleaner. Another thing I would do once the clowns are "up stream" in my aquarium is put larger rocks into the aquarium that the currents can flow over leaving a peaceful voide of current behind the rocks.. In that more peaceful area the clown Loaches could lay their eggs. Otherwise, the roe will just be swept away in the current, and that would be the end of it. There must be a safe and peaceful place with respect to water currents were the clown coaches lay their eggs.
I suspect after being able to do all the above perfectly (setting up the currents of the increasing strength, setting up the food supply to mimic nature, making the water less murky and having places for the fish to lay their eggs) the clown loaches may breed in my aquarium. I doubt that I'll being trying this out, I'm more of a thinker rather than a doer. But maybe someone will read this and give it a go in their aquarium.
Go to clown loach care (next page).