Getting decent night shots is all about the lighting tbh, I use a Canon dslr with an intervalometer makes it a doddle,96 led video light off amazon just set it to take about 20 get the fish up pose, turn it take a few more one will turn out OK usually 👍
I will only put them in a retainer for a short while while I get everything sorted, I usually let it rest in the net for a couple of mins, unhooking in the water if I can, if not get my unhooking, weighing kit out, unhook it,treat it, put it in the retainer, weigh it and put it in the water while I sort out the camera and where I want to do the snap, take a practice shot, then once I am ready, take snaps, return the fish to fight another day,