The icefishes (or white-blooded fishes) are a family (Channichthyidae) of perciform fish found in the cold waters around Antarctica and southern South America.
Their blood is transparent because they have no hemoglobin and/or only defunct erythrocytes. Their metabolism relies only on the oxygen dissolved in the liquid blood, which is believed to be absorbed directly through the skin from the water. This works because water can dissolve the most oxygen when it is coldest. In five species, the gene for myoglobin in the muscles has also vanished, leaving them with white instead of pink hearts.
Source: Science Notes & Wikipedia via Spluch