Welcome to Aquarium Sex Ed 101, I will be your instructor

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Ok, class...listen up. The above appears to be a female platy, notice behind the lower, small belly fins (don't want to get too technical with y'all), there is nothing and then there is the tail. You can't see anything there because she has an 'insie'.
Below is a male platy (not mickey mouse...but same body type). Note the small fin looking thing (light colored)between the belly fin and the tail: When in 'use' (ahem, no laughing class), it flips forward and looks like a little spear: (if you look at my siggie, it is directly above "
,publ")