Television may have changed considerably over the past decade, but there has been at least one constant: the gentle swish of a fish tail in the Roku aquarium.

The Aquatic Life animated screen saver gave the streaming company’s users a moment of calm before diving into a frenzied array of programming options. Over time, the screen saver developed a following of its own, beloved by children, cats and those looking to add a splash of color to their living rooms.

But come Dec. 1, the aquarium will go dark. Over the past week, Roku customers have been greeted with the message that they will be automatically switched over to the urban scroll of the Roku City streetscape, in all its purple glory.

The change was announced after Jim Sachs, who designed the 3D aquarium in 2000, refused to renew the license with Roku, citing Fox Corp.’s $22 billion acquisition of the streaming company, which was finalized on Friday.

In an interview, Sachs, 77, said he could not work for the Murdoch family.…