Hemoglobin (American) or haemoglobin (British) (/ˈhiːməˌɡloʊbɪn, ˈhɛ-, -moʊ-/   ); abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates (with the exception of the fish family Channichthyidae ) as well as the tissues of some invertebrates. Hemoglobin in the blood carries oxygen from the lungs or gills to the rest of the body (i.e. the tissues). There it releases the oxygen to permit aerobic respiration to provide energy to power the functions of the organism in the process called metabolism. A healthy individual has “12 to 16” grams of haemoglobin in every 100 ml of blood.