A wide variety of crabs, snails, clams, mussels, oysters and similar creatures may be collected or purchased in fish markets and bait shops. Crack the shells of mollusks such as clams to render the meat accessible to your pets. You may be surprised at the feeding frenzy that will erupt upon the introduction of a cracked clam or mussel into the aquarium.

Bait stores stock seasonally available species such as fiddler crabs and green crabs, both of which are readily accepted by many aquatic creatures.

Take care when feeding freshwater animals to your marine pets, and vice-versa. Most food animals die rapidly in alien environments, and uneaten ones will decompose quickly and foul the water. Be particularly cautious when using soft-bodied creatures such as worms because they break down very rapidly in saltwater.