Silver dollar fish are distant cousins to the piranha — and, in fact, they're native to the Amazon River — but they're herbivores and they're harmless. They stick entirely to a vegetarian diet.
They can grow up to 6 inches in length and they're delightful to own. But male silver dollar fish are among the most difficult species to sex. Here are a few tips that can help you sex and breed silver dollars.
The Anal Fin
The anal fin is longer in males than in females, and it's usually red on the leading edge. You can tell the difference more easily if you have both males and females in the tank together so you can compare them.
The Tail Fin
Male silver dollars sometimes have a dark or black outline along the edge of the tail fin.
Those Telltale Spots
When male silver dollars are interested in available females, they'll develop two black or smudgy dark dots behind their gills on each side of their bodies.
When silver dollars are ready to breed, the male becomes the pursuer. He'll appear to "chase" or tail his desired female until she relents and allows him to move up along beside her. Then some bumping and flicking will go on before the male releases his sperm. This happens at about the same time the female releases her eggs. It's not unheard of for the male to totally wrap himself around the female instead, fertilizing her eggs in a sort of fishy embrace.
Silver dollar females often lay as many as 2,000 eggs at a time.
When you've identified your male and female silver dollars, feed them a high quality diet for a week or more before moving them to a breeding tank. The tank should be dimly lit with soft water at about 8 dGH or less.
Keep the temperature at 80 to 82 F. You'll also want to provide plenty of leafy plants for a soft landing spot to catch the eggs and keep them safe until they hatch.
Silver dollar fry will typically hatch within three days, but may take a little longer. Because silver dollars are not carnivorous, the adults won't eat the eggs. It's perfectly safe to leave the whole family in the tank together, but the fry usually do better on their own. It takes up to nine days before they'll begin swimming about freely on their own. They should reach adult size within eight months or so.
If All Else Fails
If the challenge of differentiating between male and female silver dollars is too much, consider buying six or so juveniles and letting them grow up together. The males and females will typically pair off on their own with no help from you. In fact, it's recommended that you raise silver dollars in groups. They tend to be very social fish and they will generally only breed if they're not too isolated. Always keep them in schools of at least five.