In order to make feed nutrients for sinking fish feed be absorbed by fishes to the greatest extent, pelleted sinking fish feed made by fish feed should have good stability. On the other hand, because the digestive tract of fishes is short, the ripening degree of pelleted sinking fish feed has great influence on the growth of fishes. So the ripening degree is an important factor for identifying feed quality. Sinking characteristic of sinking fish feed in another important factor. Good quality sinking fish feeds can all sink in the water and the fishes can consume it.