These brown pellets that resemble croutons your mom used to throw on salad are actually tubifex worms for fish.
These high protein freeze-dried pellets are the the perfect treat for your tropical fish. Just moisten the cube product, slightly broken up, and stick it to the inside glass of your aquarium. Watch your fish circle around and nibble at the cube. The remaining pieces that are not eaten should not be left in the tank overnight.
Ta-Dah! That is all there is to giving your tropical fish a nutritious snack.