As previously mentioned in
https://forums.thinkfish.co.uk/general-fishkeeping-chat/musings-re-more-fish/msg51690/?topicseen#new , I have taken in a neighbour's fish for adoption.
Throughout the first fortnight in the QT, the fish have adapted well, are behaving normally, shoaling nicely, actively playing by swimming through the ornaments, seem to have enjoyed the addition of a live plant, are eating well, buoyancy is good, etc.
Mr FCMF thinks they're very healthy due to the above and as they're large, and thinks they ought to be moved across into the main tank as the volume is 3x that of the QT and the downsize to the small environment from a tank of ~6x the volume might do more harm than good.
However, my trained eye, plus extra vigilance / natural protectiveness towards the existing fish in the main tank (esp after poor experiences with cardinals), notices other aspects that he doesn't and most others wouldn't.
My experience of keeping cardinals has taught me that optimum-health ones are those which
maintain an extremely intense blue and red line the
entire length of their bodies including gills and tail and are of a standard shape, as per the remaining two in my main tank. I was immediately aware that the fish in my neighbour's tank were of sub-optimum quality for various reasons including this but did wonder if the light substrate, barer top of the tank, stronger lighting and larger body mass than any cardinals I've had before may have contributed to how noticeable this was. The other issues that I'd noticed but hoped might resolve or be addressable in quarantine were the following:
Fish 1: very large and bloated, likely a female carrying eggs but beyond a healthy size esp when viewed face-on [based on past experience, I suspect she'll succumb to dropsy in the future];
Fish 2 and 3: gill plates different - standing out rather than sitting 'flush' against the body and thus exposing the red gills - if this had been caused by ammonia, I would have expected this to have resolved following a fortnight in my ammonia-free QT, or if a problem I might have expected accompanying strange behaviour or other symptoms, so now thinking this is simply "natural variation" (eg a quick internet search reveals that some fish have short gill plates as per a discussion re koi/goldfish breeding);
Fish 3: has a small mark on its side which I
think is simply a missing scale [this has not changed or developed a fungus or other problem during the fortnight in QT];
Fish 4: looks ok although a different shape to any I've had before - likely a female with a convex tummy (ie comes down into a point).
I'd appreciate your thoughts on these and esp the gill plates ie whether this indeed might just be some form of 'natural variation' or whether there is anything I can do while they are still in the QT other than ongoing monitoring for the next fortnight that all remains well otherwise - or even whether there's any merit in keeping them in the QT for another fortnight as originally intended. NB. Have tried to take photos and video footage but difficult as the QT has no light in it and is getting reflections from the main tank and windows, and it probably won't show much up anyway. Many thanks in advance.