Group of two-week-old T. thacbaensis f1
Why would these tiny, bite-sized, fish be more brightly colored than their parents? I’ve now raised four species of minnow whose babies have a bright, eye-catching stripe that the parent lacks: three kinds of Tanichthys, and Danio choprae.
It seems idiotic for something so tiny to be so conspicuous… they may as well swim around on little plates carrying little bottles of barbecue sauce. I don’t think it’s a cue for schooling, because the Tanichthys fry don’t school until they grow up, lose the bright line, and assume adult coloration.
My best guess is that it has to do with parental recognition. Almost every kind of minnow will cheerfully devour its offspring; Tanichthys is unique in that parents and fry can coexist without any intergenerational cannibalism. That doesn’t account for Danio choprae, though — they eat their eggs and fry just like any other danio, so maybe something else is going on there.
This post serves as a note to self: I need to get some albino T. albonubes and see if their fry lack the blue stripe, and if so, if that affects parental predation.