Than they probably were parasite infested from the LFS.. As far as i know they are wild catch and not yet captive bred. Good thing to learn and recognize when fish are not healthy or show depressed behaivor.. It's hard to explain in words what to look for, i kinda learned it over many years trail and error. And now i see at first glance when not to buy and leave them in the shop and wait a few weeks for another batch to arrive. With boraras/rasboras they should be full color with a somewhat silvery shiny round belly. If they are pale and or skinny or belly is even worse and concave. Than do not buy.. Tho experience makes you see if it concers very young fish that still are in transition periode from larval stadium to young adult, these always look skiny and flat and have relative to body size i bit larger eye. Learn to see these small details, the smaller the fish are the smaller the details to overlook. Belly should never be concave in shape.
But the Kobutai are realy very lovely little fish.. In my tank they also regularly play in the filter outlet stream.. Healthy specimen are extremely playfull and constantly showingh sham battles and chasing eachother back and forth around the tank..
Cheers for the info, I cant really recall what they looked like when I first got them, the few remaining are very big now (compared to the other boraras I keep) seem healthy and very active, like you said they zip around and show the other fish who is boss... even tho there is only 3 of them and about 30 other boraras.
I have a few golden mountain minnows in one of my outdoor thanks that I want to rescape so they will be the first fish into this tank, I may just stick with mountain minnows