On fish A there is a decent bulge of the body just after the operculum odontodes, visible against the pectoral fins. But fish B also has this but a little less pronounced. The only other significant difference I can see is in pic 4, the fish on the left seems to have a more angular body whereas the other is more rounded. Anything to read into?
If you could get a pic of their vents, I think that would help.