Just make sure they're the right species. San Francisco Brand - Sally's silversides are the best IMO. They come in a frozen flat. Unlike some other brands, these are frozen in a bit of water. Keeps them fresh and looking like they're still alive. The species is Hypomesus olidus or "Arctic pond smelt". Doesn't actually live in ponds though. It's a freshwater fish found in cold rivers in the Arctic.