The pipefish is a long, narrow tube-shaped, colourful sea creature, with a flexible tail with which it can anchor itself to objects below the sea - just like the seahorse family, of which it is a member, in fact it is often unkindly referred to as a seahorse, straightened out.
The London Zoo Aquarium was first built in 1853, by Philip Henry Gosse, not just an architect but a specialist in marine life with a large collection. His design was spectacular, with huge plate glass windows giving maximum exposure to the creatures within, most of which were from his own collection. He also invented the word aquarium, taking just the front and back from the Zoo's own rather unwieldy suggestion of Aquatic Vivarium.
That building was replaced in 1923, with a grand opening by King George V and Queen Mary. This is probably what gave the idea for these cards. The design made maximum use of rather limited space, and extended down and underneath the animal enclosures.
However like its contemporary, Wembley Stadium, there was a limit to how much the concrete it was built in could endure, and in 2019 it was closed to the public for the final time. New plans are to reopen an aquatic facility of some kind elsewhere in the grounds, but there is no word on whether the vacant and crumbling aquarium will be demolished.