The shadowing behaviour has not stopped. I wish I could do a good video but they are really at it when the lights are off. I have another small tank in there that emits enough light for me to observe the loaches when their light is off.
If I didn't know any better, I'd say what my clown loaches are doing is mating behaviour. I know they are impossible to breed naturally in captivity but I'd guess its not stopping them from trying to mate.
Two of my loaches are definately females. They are quite larger than the rest, bulkier too. I was able to measure one of them a week ago and she's about 9 inches. She is the oldest. I bought her 3 years ago when she was about 5-6 inches long already. The second one, judging by the size difference is possibly 7-8 inches long is a 4 years old whom I bought together with another 4 loaches.
The rest of the group consist of the 4 four years old slimmer loaches, one 1.5 years old and a new baby loach only a few months old I'd assume.
Today at first I saw the 4 older slim loaches chasing either female they came across and shadowing them. They were fighting amongst themselves each trying to get a closer position to the female.
The females, whomever they were at, would violently try to swim away from them and didn't seem to be enjoying whatever they were doing. The slim ones, males assumed, once 'shaken off', would then start swimming in circles amongst themselves around the tank for a few moments, quite fast....with sort of their noses together, bodies next to each other. ..It looks like they were shadowing each other too, only that these loaches are all about the same length and age and all 4 were gathered in a very tight bunch moving in circle like behaviour. While doing that, they'd come across one or two of the female who were literally sitting around the tank sides. Then the chase starts again, all 4 against one, then breaking off in groups when seeing the other female, trying to chase her too in exactly the same manner.....
To me it seemed like the males are showing off to the females, then trying to mate with them.
I bred corydoras and the spawning starts almost exactly the same way. Males would chase the females around the tank like mad, and fight amongst themselves while trying to get to the chased female. Eventually one male wins and mates with the female in a T position. Only that the loaches don't get to the part of the actual spawing, just spawning like behaviour.
I could be wrong, but that's what it looks like to me. I don't ever recall seeing my fish so desperate at "shadowing" each other. Whatever it is, it is certainly intriguing.