Sexes of Fish

Question
How can I tell the different sex of some fish?  I just got a 20 Gallon Tank and we have Glass Painted Tetras (I didn't know about them being dyed or else I wouldn't have bought them), Red Eyed Tetras, Mickey Mouse Platy, Hoplo Catfish, Corydora Catfish and Algae Eaters.  If you can give me information on my fish, that would be great.  Thanks!

Answer
Hi Peggy,
  With some fishes it is easy to tell, and with others it is almost impossible.  For instance, with the corydoras catfish, females tend to be larger and have a different profile when you look down on them from above -- they carry their weight in the belly more.  For the platys, because they are livebearers, males and females differ in the shape of the anal fin (the one on the bottom towards the back).  In the female it is a normal fin but in the male it is modified into a "gonopodium", which is a fancy name for a penis-like structure, used for getting sperm into the female.  As for the hoplo catfish, algae eaters and tetras, I don't have any experience with them so I don't know. Sorry.

-- Ron
  rcoleman@cichlidresearch.com
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