The epithet is literal: his long nose-bill is shaped like a sword-saw with serrated edges, visible in close-ups (page 14, panel 1). Name-as-anatomy — a recurring Oda technique.
Forward-payoff: Arlong uses his nose as a sword-substitute in combat (Ch. 89-91). The Saw-Tooth epithet is doubly-loaded: (a) shark-tooth anatomy (literal teeth in his mouth), (b) saw-tooth nose (combat-weapon). The chapter installs both readings in a single panel.
Payoff
Update Ch. 92 — operationalized as named-weapon canon + arsenal-as-name escalation
Ch. 92 operationalizes the Saw-Tooth epithet at two levels:
Anatomy as named-projectile-weapon — Shark Darts (pages 3-4): Arlong launches himself like a torpedo, saw-nose-first. The saw-nose is now a named-attack combat-vocabulary item, not just a visual species-marker.
Arsenal-as-name — Shark Saw (page 13, named by Nami): a massive detached saw-toothed sword-class weapon stored in Arlong Park’s interior armory, mirroring Arlong’s saw-nose at amplified scale. The Saw-Tooth epithet operationalizes a saw-class weapon arsenal, not just nose-anatomy.
The chapter resolves the epithet’s what-does-the-saw-actually-do question with two distinct combat-deployments. Status: escalated from anatomy-only-tell to operationalized-combat-arsenal.
Ch. 93 — Shark Saw eaten and destroyed in chapter-opening panel