Determining gender on X-Ray Tetras ("Pristella" Te

[Kilgore]

Hello,

Asked this question on another forum and didn't receive an answer, so thought I would try again here. I rescued some fish a while ago, and two of them were Pristella maxillaris "X-ray tetras," aka Pristella aka Goldfinch tetras. I noticed that one is smaller and more timid, with less vivid coloration on the fins - is that the male or female? I haven't been able to find anything in the literature about differentiating between the sexes on these fish, except that males are supposedly "thinner." Does thinner mean smaller? In tetras that show sexual dimorphism the males is usually more showy, right?

Also, I was thinking of moving these guys in with some guppies I have in a 20 gallon. They seem very passive and not likely to nip fins, and they don't look big or fast enough to eat fry. Anyone know otherwise? Let me know. If I move them, I can get more of them, too, for a proper school.

Thanks!

 

[SerLunchbox]

Sexual Differences:
The male is more slender with a sharply pointed swim bladder. The female is more rounded and you can actually see the eggs in a mature female.

Hope that helps
http://animal-world.com/encyclo/fresh/characins/pristella.php

That should help you with what you are looking for (completely)

 

[kc2ped]

I have five X-ray Tetras. Four of them follow the standard description. The fifth, and smallest, has on orange tag on the anal fin in place of the usual yellow. I know the conventional wisdom is that males are smaller than females but I don't know the relative ages of the fish in my school and can't be sure that the fish in question wasn't the runt from a spawning. And they won't stay still for me to compare the shapes of their swim bladders. I am wondering if the orange tag might be an indication of that fish's sexual orientation.