I have 6 Black Skirt tetras. 3 of them cycled my tank for about a month. The other 3 joined about a month and a half after the cycling started.
Here is what the first three look like:
Here is one of the first three next to one of the new ones (kinda blurry):
And this is what the newer ones look like:
Notice the fins. The older ones have mangy looking fins and they are longer. The new ones have nice perfect fins. Do they grow over time? The old ones' fins have almost doubled in size in just over a month...