Robotic goldfish are artificial, realistic looking goldfish kept in a water filled fish tank. They last longer and are low-maintenance compared to real ones, in theory.
They are kept in a water filled fish tank in his sleeping quarters, and he apparently bought them on Titan since there is a "souvenir of Titan" sticker on the fish tank, like much of Lister's "junk" (although the episode "Ouroboros" would suggest they were bought on Mimas, although this did occur in Kochanski's dimension. In the novel Infinity Welcomes Careful Drivers, Lister bought them on Miranda).
They are identifiable because Lennon tends to work fine, with little to identify it from a real goldfish. However, McCartney is consistently shown to be defective, and swims backwards.
When McCartney stopped working, Lister was able to fix him easily with a screwdriver after bashing him on the desk to determine his status.
The Cat believed them to be real fish, and later tried to eat either Lennon or McCartney, only being stopped by Lister tackling him to try prevent a vision of the future he had seen. The Cat still lost a tooth in the incident anyway. The incident upset Lister, since it seemed to prove that the future was inevitable, and Rimmer had already seen an apparent future echo of Lister dying. (RD: Future Echoes)
A group of larger fish are seen on the display screen of the Officer's Quarters in around Series IV. However, it is never made clear whether this is meant to be Holly's screensaver, real fish, or more electronic fish.
Like Red Dwarf itself and the original crew, Lister's robot goldfish make a return in the sleeping quarters at the beginning of Series VIII, having been restored by the nanobots. However, McCartney is still defective. (RD: Back in the Red I) In the deleted scenes of the episode, Lister is seen repairing McCartney by banging it against the side of the fish tank.
When Lister and Rimmer were imprisoned, the goldfish were later moved to their cell in The Tank. Rimmer said that the goldfish winced when Lister played his guitar, and hid under the plants when they heard Lister tuning up. (Krytie TV deleted scenes)
Lennon and McCartney are once again seen in the sleeping quarters of Series X, albeit easy-to-miss. Rimmer once told Lister that he was becoming lazy and, as an example of this, reminded Lister that he couldn't be bothered to make a cup of tea, instead dunking his biscuits in the fish tank. (RD: Dear Dave)
Behind the scenes
- He is presumably named for Sir James Paul McCartney.
- One of the Red Dwarf novels, Better Than Life, says that Lister adored junk and electronic crap. Accordingly, he had collected the robot goldfish, an alarm clock, Talkie Toaster, a musical toilet-roll holder that plays "Morning Has Broken", and an electronic chilli thermometer for measuring his curry from "Very Hot" to "Book a Plot in the Cemetery, Matie". The other items were acquired by Lister from a souvenir shop on Miranda, so it is likely Lennon and McCartney were too.