The largest extant fish: adults typically 8–12 m TL but verified records exceed 18 m and 30 t. Body fusiform and massive, head broad and flattened with a terminal mouth up to 1.5 m wide containing ≈ 3 000 minute teeth arranged in 300 rows. Five large gill slits house filtering pads. Dorsal surface dark bluish‑grey to chocolate brown patterned by hundreds of white/yellow spots and transverse stripes unique to each individual; ventrum white. Two dorsal fins, first triangular and set posterior to pectorals; caudal fin semilunate with longer upper lobe in juveniles. Skin up to 10 cm thick, covered in large denticles. Sexes similar; males possess paired claspers.
The largest extant fish: adults typically 8–12 m TL but verified records exceed 18 m and 30 t. Body fusiform and massive, head broad and flattened with a terminal mouth up to 1.5 m wide containing ≈ 3 000 minute teeth arranged in 300 rows. Five large gill slits house filtering pads. Dorsal surface dark bluish‑grey to chocolate brown patterned by hundreds of white/yellow spots and transverse stripes unique to each individual; ventrum white. Two dorsal fins, first triangular and set posterior to pectorals; caudal fin semilunate with longer upper lobe in juveniles. Skin up to 10 cm thick, covered in large denticles. Sexes similar; males possess paired claspers.
Epipelagic and mesopelagic of warm seas (18–30 °C), surface to ≥ 1 900 m; in Costa Rica observed offshore of Nicoya & Dulce gulfs, Cocos Ridge seamounts, occasionally Caribbean slope. Aggregations coincide with up‑welling, fish‑spawn slicks and tuna purse‑seine sets.
Planktivorous megafauna; filter‑feeds on zooplankton, fish/squid larvae, coral spawn, pelagic eggs; occasionally surface‑ram feeds on small schooling fishes
Social Structure & Behaviour
Activity pattern: primarily surface‑oriented feeding dawn/dusk; deep dives midday.
Grouping: generally solitary; seasonal feeding aggregations of 5–30 around plankton blooms or fish‑spawn slicks.
Movements: long‑distance migrations along Costa Rica Dome–Cocos–Galápagos ridge; site fidelity to thermal fronts with high zooplankton fluorescence.
Communication: no documented acoustic signals; tactile cues with trailing fishes/conspecifics observed.
Special behaviours: vertical “corkscrew” feeding spirals and passive suction at fish‑egg slicks; tolerates close approach by remoras and pilot fish.
Each spot pattern is unique—photo‑ID uses algorithm adapted from NASA star‑field software.
Can filter ~6 000 L h⁻¹ of seawater while swimming 1.2 m s⁻¹.
Performs diel vertical migrations: surface feeding at dusk, dives > 1 200 m likely for foraging or thermoregulation.
Documented hosting up to 50 remoras and juvenile trevallies sheltering within gill slits.
In 2023, a 12.5 m female tagged off Cocos travelled > 4 800 km to Galápagos and back in 7 mo.
Native
Decreasing
