The Laughing Fish was partially based Steve Englehart's Joker two parter from his Detective run. Especially the fish part,Yes. B:TAS played it seriously, but not to the point of relentless grimness. It was probably closest in tone to the Batman comics of the '70s, their heyday under Dennis O'Neill. Most of the comics stories it adapted more or less directly, like "The Laughing Fish" and the Ra's al Ghul 2-parter, were from that era.