Blue Hippo Tang (Paracanthurus hepatus)

Paracanthurus hepatus is the fish that launched a thousand reef aquariums after Finding Nemo, but the real animal is considerably more interesting than the cartoon version. That electric-blue body with black "palette" markings and yellow tail hides a retractable scalpel blade at the caudal peduncle — a keratin-sheathed spine that surgeonfish deploy during territorial disputes — and startled individuals will jump from open-top tanks without warning. They do it fast enough that it looks like the fish teleported out of the water.

Juveniles wear the same electric blue with cleaner, sharper black markings; as the fish matures, the markings soften and the black pattern expands slightly. In the wild, juveniles aggregate in branching coral colonies (Pocillopora, Acropora) for shelter, retreating into the coral structure when threatened — behavior that's completely impractical to replicate in captivity but explains why they're naturally skittish in open environments without adequate rockwork refuge.

They're herbivores that need nori and algae-based foods as the foundation of their diet, not just fish food they happen to accept. A Blue Hippo Tang fed primarily on meaty foods develops HLLE (head and lateral line erosion) over time — the pitted, discolored skin that marks a fish maintained on an inadequate diet.

Scientific name: Paracanthurus hepatus
Origin: Indo-Pacific — branching coral zones and reef crests from East Africa to the Pacific, especially common in the Philippines, Indonesia, and the Coral Triangle
Water parameters: Temp 74–82°F · Salinity 1.023–1.026 · pH 8.1–8.4
Tank requirements: 125 gal minimum; 180+ gal preferred; needs extensive swimming room and rockwork refuge
Diet: Herbivore — nori seaweed and algae-based foods must form the majority of the diet; supplement with meaty foods
Compatibility: Semi-aggressive with other tangs; reef safe; provide adequate space to prevent territorial conflict
Husbandry note: Cover open-top tanks. Blue Hippo Tangs jump at high speeds with essentially no warning and will find any gap in screening. This is not a theoretical risk — it's the most common sudden death cause for this species in home aquariums.