Silver Dollar

Taxonomy and False Piranhas:

They belong to the family *Serrasalmidae*, which makes them close genetic cousins of the feared *Pygocentrus nattereri* (Piranha). However, the dentition of *Metynnis* is not formed by the iconic crossed triangle blades, but by blunt teeth perfect for cutting and grinding plant stems and seeds.

Role as Dither Fish:

Their role par excellence is the "reassuring target fish" (dither fish) in tanks for large territorial cichlids. The Cichlids, seeing this bright school swimming serenely at mid-water, are reassured about the absence of external predators and will come out of their rocky dens without fear. The round and expanded shape of the Dollars will also discourage even a large Oscar Cichlid from trying to swallow them, as they would not fit in its mouth apparatus.

Tank Setup (No Live Plants!):

Attempting to keep live plants in an aquarium with a school of *Metynnis* is like trying to grow lettuce in a chicken coop. A school will chew a forest of *Echinodorus* or *Cabomba* down to the bare sand in less than 24 hours. The decor must consist of intricate branches (reaching the surface), bare boulders, and at most, for visual impact, high-quality thick plastic plants. They are fish known for panic: do not place the aquarium behind a slamming door. When frightened, they rocket off and can seriously injure their mouths against the glass.

Vegetarian Diet:

Their hardiness will quickly decline if forced to eat carnivore feeds, which will cause intestinal blockages. They must receive massive daily doses of vegetables. Clip fresh spinach leaves, romaine lettuce, or zucchini strips to the glass and watch them flock. Add spirulina wafers. They like to supplement this diet with live/frozen foods or protein pellets once or twice a week.

Filtration:

High mobility in a group combined with a massive intake of fiber produces a fair amount of solid fecal waste. The water must remain crystal clear and moving, requiring excellent external canister filters.