Here's a picture of the two of them from a scene in Return of the Jedi.

Can you guess which one is which?

The Mon Calamari are said to be the soul of the Rebel Alliance. The Empire pressed these gentle, amphibious people into war by subjugating their watery world. In retaliation, the Mon Calamari became one of the key species of the rebellion, supplying badly needed warsips to the outnumbered Alliance fleet.The most respected of the Alliance Mon Calamari is Admiral Ackbar, leader of the fleet. The stern gravelly-voiced tactitians led the fleet as it engaged the Empire at the critical Battle of Endor.The Mon Calamari people are humanoid, about 1.7 meters tall. They have salmon-coloured skin, high-domed heads, webbed hands and large, goggle-like eyes

www.starwars.com/databank/species/moncalamari