The correct answer is option 4 - Oyster. Pearls are harvested from oysters. Oysters are bivalve mollusks that live in saltwater or freshwater habitats. When an irritant, such as a grain of sand or a parasite, enters an oyster`s shell, the oyster secretes a substance called nacre to protect its soft inner body. Over time, layers of nacre build up around the irritant, forming a pearl.

Option 1 - Prawn: Prawns are crustaceans that are often eaten as food. They do not produce pearls.

Option 2 - Pila: Pila is a genus of freshwater snails. These snails do not produce pearls.

Option 3 - Tuna: Tuna is a type of saltwater fish prized for its taste and used in many seafood dishes. Tuna do not produce pearls.

In summary, pearls are harvested from oysters, not prawns, pilas, or tuna.