I have a 10 gallon with 3 amano shrimp and 2 red cherry shrimp. I was wondering if it was possible to sex the shrimp. Also how easy is it for them to breed in my tank? Why is one cherry shrimp significantly smaller than the other one even though i bought them at the same time and same size
Females shrimp are pretty much always larger than males, sometimes up to twice as large. They will also have a dark patch in their "head" called the saddle which is pretty much developing eggs. If you have a male and female, a safe filter and their are no predators in the tank then I bet you will have some little shrimp before too long.
It looks like a yellow or green "U" shape behind the head on RCS, but since yours are a deep red you won't be able to visibly see their saddles. Females also tend to have a rounded stomach for carrying eggs, the first RCS looks female imo.
As for amanos they have the patches too but they're harder to see since they blend in with the color of the amano. Female amanos still have rounded stomachs though and usually have a line of dashes on their sides, males will only have dots. Both RCS and amano females are much bigger than males however.