Episode 18 of "Futurama"
s02e09 Why Must I Be A Crustacean in Love

Leela and Amy drag Fry to the gym, and Zoidberg feeling extra energized, joins them. Zoidberg soon starts acting weird and getting violent. After being examined by Farnsworth, he tells the crew that it must be mating season on Zoidberg's planet. While taking him home for mating, Zoidberg informs Fry that there is no such thing as love for his species. Once there, Zoidberg is unsuccessful in finding a mate, and is even rejected by a female he used to know, Edna. Fry decides to help Zoidberg by teaching him how to romance a girl. It seems to be working, and Zoidberg starts feeling these weird emotions for Edna. Unfortunately, once Edna finds out it was Fry behind this, she falls in love with him! In a jealous rage, Zoidberg challenges Fry to Claw Plach, a fight to the death! During the fight, Zoidberg cuts Fry's arm off. The fight is stopped when the mating Frenzy has begun. Edna went off to mate with the emperor of the planet. Zoidberg is upset that he missed the frenzy, but at least he's alive because their species dies after mating.