and then there were two

[Innesfan]

If all three are sparring, they're males. Females don't spar. And that photo is great.

 

[seangee]

If all three are sparring, they're males. Females don't spar. And that photo is great.

That's a really useful insight - and one I have not encountered before, although admittedly most of what I think I know has been gleaned on-line or through personal observation. But it does put it beyond any doubt.
Oh well back to the drawing board. One way or another I'm not putting this small group back into the community. I had forgotton how different their behaviour is when they feel secure so I suspect they will have some friends of their own kind in the very near future.

I also hope my heart can take it . In the big tank you don't notice how completely motionless they are when sleeping. This morning when I turned on the room light all 3 were in the frogbit roots at the front of the tank. It felt like an eternity before I detected any sign of life - and it was too dark to see if the gills were moving.

 

[seangee]

For those who don't know this is from the seriouslyfish.com species description.

Don’t worry if your fish look different when you switch on the aquarium lights after dark or in the morning as like most Nannostomus species it assumes a paler, cryptic colour pattern at night, in this case the dark lateral stripes disappear and two oblique bars are visible posterior to the dorsal-fin.

This diurnal rhythm has been show to occur in blind specimens, suggesting it’s an automatic response that the fish cannot control.

I have never managed to capture this because cameras don't work well in total darkness and I am not willing to trigger a flashgun inside the tank while the fish are sleeping. I saw it this morning, exactly as described, but by the time I crossed the room to get my phone the metamorphosis was already well under way.