In milkfish (Chanos), the gill cavity contains epibranchial (suprabranchia) organs dorsally on each side, consisting either of simple blind sacs or elaborate, spirally-coiled ducts. The organs occur in several relatively unrelated families of lower teleosts and apparently relate to the kind of food eaten. Those fish with simple ducts all eat macro-plankton and those with the larger ducts microplankton. Although their function is unknown, concentrating the plankton has been suggested as a possibility