I have a group of about 20 eastern blacknose dace in my quarantine tank currently waiting for their new home to be built. Its mostly mature fish but there are a couple of juveniles in there as well. I have noticed that when I show up for feeding time, sometimes there is an adult or 2 or 3 that look different then the others. Their splotches are much more prominant and their black line is more copper color then black. Within seconds of starting to feed all of this fades away and they are back to their more typical coloring. Today I snuck a picture before it faded.
To those with experience with this fish, is this mating colors? Or is this a sign my fish is stressed out? Or something else? Thank you for any information.