So, my buddy has a pair of Angels that spawned several times yielding over 1000 viable fry. Male g/g, S/+. Female gm/+, s/+. The offspring all look like you would expect: silvers, ghosts, gold marbles, gold marble ghosts, blushers...all in the expected proportions. Then there is one dark fish. This begs the question: is this a spontaneous reappearance of the "D" dark gene or something different.

If it is the known "D" gene, the fish is not dark enough to be a hybrid dark. It looks like D/+, S/+, that is to say it is a dark gray with a vaguely visible spot like you would expect.

In a month or two this fish will reach breeding age. Do you have any particular suggestions on who try to pair it with in order to figure out if this is the usual "D" gene or something else? Has anyone had a similar experience? If so what did you find?