Jim the Fish was a friend of the Eleventh Doctor and River Song, whom they met on one of their adventures. When they met him, he was building a dam. He was still doing so some time later when the Doctor checked up on him. (TV: The Impossible Astronaut) When Flemming was reading River's diary, he mentioned this adventure. (TV: The Husbands of River Song)
In the diary, River wrote about a discovery she made on the sixty-fifth day of a dig site on Anteria XVI Cordobane: in a bar run by the Brotherhood of Maldovar, in the 48th century as far as River could remember, the Doctor took her and Jim out for karaoke. River did not remember very much of the night, except for the song "Islands in the Stream" and a video recorder, but the tape they made of that night was ultimately lost. Some time later a series of paintings on sandstone slabs were unearthed on Anteria XVI Cordobane, revealing "Jim the Fish in that suit in that bar singing that song, gills flaring, teeth sparkling under the glitterball". River and her colleague, Sssibeth, deduced that each tablet represented a line in the song, a phenomena Sssibeth thought he'd seen before. They believed that some kind of love religion had been created around the images. (GAME: The Eternity Clock)