Thresher sharks
Alopiidae line

Characteristic features:

  • Precaudal tail much shorter than trunk
  • Upper lobe of caudal fin broad and extremely elongated, about half of total length
  • Subterminal notch on caudal fin


Key adapted from Compagno, 2001.1

Alopiidae species
    1. Head nearly flat between eyes (Fig. 1a); eyes very large, directed upwards and clearly visible in dorsal view (Fig. 2a); a deep horizontal groove on each side of nape above gills (Fig. 3a); first dorsal-fin base closer to pelvic-fin bases than pectoral-fin bases (Fig. 4a); 25 rows of teeth in each jawAlopias superciliosus (Bigeye thresher)
    2. Head strongly arched between eyes (Fig. 1b); eyes smaller, not directed upwards or visible in dorsal view (Fig. 2b); no obvious groove on nape (Fig. 3b); first dorsal-fin base about midway between pectoral and pelvic-fin bases, or slightly closer to pectoral-fin bases (Fig. 4b); 29 or more rows of teeth in each jawAlopias pelagicus (Pelagic thresher)

Similar families:

Stegostoma fasciatum
Stegostomatidae are similar to Alopiidae in having a caudal fin about half the length of total body length. Stegostomatidae differ in having a barred or striped body markings (vs. no makings in Alopiidae); nasal barbels (vs. no barbels); transverse mouth in front of eyes (vs. mouth extending well behind eyes); small tricuspid teeth (vs. small blade like with erect to oblique cusps, cusplets small or absent); first dorsal fin located over pelvic-fin bases (vs. located within pectoral- and pelvic-fin interspace); second dorsal and anal fins large (vs. minute) and no ventral caudal fin lobe (vs. short but strong.


Alopias pelagicus
Pelagic thresher
Alopias superciliosus
Bigeye thresher


  1. 1.
    Carpenter K, Niem V, Compagno L. Alopiidae. In: FAO Species Identification Guide for Fishery Purposes. The Living Marine Resources of the Western Central Pacific. Volume 2. Cephalopods, Crustaceans, Holothurians and Sharks. Vol 2. Rome: FAO Library; 2001:1269-1273.