Different Colored Dorsal Fins

[chibi]

I have 5 Von Rio/Flame Tetras in my tank, and noticed that some of them have red dorsal fins, while others are clear. Is it a genderal difference or something? I can't figure it out...

 

[Lateral Line]

In most cases, more colourful fish are males, less colourful, female. In this case, Hyphessobrycon flammeus, the difference between the sexes is not usually in the red however. The males dorsal is elongated relative to the females, and the female tends to lack completely, or at least partially, the white marking in the anal fin.

If the fish that are showing the red colour are generally brighter and slimmer, then you are probably seeing some sexual dimorphism. If not, then it is probably a stock quality issue.