Over the past 2 years or so I've had a regular "spawning" group of Silver dollars. I believe I have two females (5-6 inchers) and one male (4 incher) and recently acquired four smaller ones (2f:2m?) who've spawned for the first time (to my knowledge) this month.
Every month (if I give them regular light-8hrs per day etc) they do their thing and do so for 3-4 days in a row. Squirting eggs all over their tank.
I've not gotten any fry due to their tank mates eating all their eggs shortly after dropping.
Perhaps I'll remove the egg eaters for a few months & get a successfull spawn-we'll see.