Sexing and Breeding Silver Dollars

silver dollar fish in a group
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Native to Amazon River Basin and other parts of South America, the Silver Dollar fish refers to many species mostly in the genus Metynnis; these are distant cousins of the piranha. Yet all Silver Dollars are harmless herbivores; they stick to an entirely vegetarian diet.

These fish can grow up to six inches in length and are a delightfully flashy addition to any tropical freshwater tank. Breeding them in captivity is easy, yet male Silver Dollar fish are among the most difficult species to identify by sex. There are, however, a few hints that can help you sex your fish for breeding.

Color Changes and Subtleties

Telling the difference between males and female Silver Dollars is more easily done if you have both genders in the tank together to compare them side by side. The anal fin is longer in males than in females, and there is usually red pigment on the leading edge in healthy males. In addition, male Silver Dollars sometimes have a dark or black outline along the edge of the tail fin. 

When male Silver Dollars are interested in available females, they will also develop two new telltale black or smudgy dark spots, one behind each operculum (gill covering). These are known as breeding spots and indicate healthy hormonal changes.

If the challenge of differentiating between male and female Silver Dollars is too difficult, consider buying six or so juveniles to let them grow up together. The males and females will typically pair off on their own with no help from the hobbyist. Typically, it's recommended that you raise Silver Dollars in these groups because they are very social fish; they will generally only breed if they're not too isolated. Always keep them in schools of at least five.

Breeding Tank Setup

While you are identifying your male and female Silver Dollars, feed them all a high-quality diet for a week or more before moving any fish pairs to a breeding tank. Your adjunct tank should be dimly lit with soft water at about 8 dGH or less. Keep the temperature at 80–82 degrees Fahrenheit. Provide plenty of leafy plants to make a soft landing spot to catch the eggs, keeping them safe until they hatch. 

Breeding Behavior 

When Silver Dollars are ready to breed, the male becomes a pursuer. The male will appear to chase until the desired female relents, allowing closer contact. 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 unusual for the male to wrap himself around the female in a fishy embrace. Silver Dollar females often lay as many as 2,000 dispersed eggs during a single mating. 

Silver Dollar Fry

Silver Dollars will typically hatch within three days but may take a little longer. Because they are not carnivorous, parent fish and neighboring adults will not eat the eggs. It's perfectly safe to leave the whole family in the tank together, but the fry usually forage better when they don't have to compete with adults for the same food. It takes up to nine days before the fry will begin swimming about freely. Silver Dollars will reach adult size in about eight months.