Obviously this is a sequel to the original series episode The Trouble With Tribbles, featuring the same Cyrano Jones as the itinerant ne'er-do-well who introduces tribbles to the Enterprise, and the same Captain Koloth as the Klingon antagonist.

A major visual difference in this animated episode is that both the tribbles and Koloth's uniform are coloured pink, rather than the light brown that both were in the live action episode. The reason for this is that Hal Sutherland, the founder of the Filmation animation studio which produced the animated series, and the director of this episode, was colour blind. He assigned the colour pink to the cels, thinking it was a light grey, and by the time anyone who knew what colour tribbles were supposed to be noticed, it was too late in production to change it.

Transcript

1
Captain's log, Stardate 5392.4. Escorting robot grain ships to Sherman's Planet.
Sulu: Klingon vessel, closing on a small scout ship.
Kirk: Beam the pilot aboard, Mr Sulu!
2
{transporter room}
Kirk: Cyrano Jones!*
Scotty: And tribbles!
Cyrano Jones: They're genetically engineered safe tribbles. They're pink!
Caption: * See: The Trouble with Tribbles.
3
{bridge}
Kirk: Captain Koloth.
Koloth: {on viewscreen} Kirk. Hand over that fugitive!
Kirk: Gladly!
Spock: Ahem...
Kirk: I mean: No! He's a Federation citizen!
4
McCoy: The tribbles are eating the grain we salvaged, but not reproducing.
Cyrano Jones: Told you they were safe. And this glommer eats tribbles!
Kirk: Uh... {looking at a giant tribble in the corridor}
5
Sulu: The Klingons are preparing to board!
Kirk: Beam tribbles into their airlock!
Spock: The moral of this tale: Ecological warfare is superior to conventional weaponry.
6
McCoy: But if we poke these giant tribbles...
SFX: Pop!
{hundreds of small tribbles fall on Kirk}
Kirk: Why do I feel like we've done this before?