Arapaima gigas (Cuvier, 1829)
Species overview
Very large fish, one of the largest freshwater species. Outlines of back and belly straigth. Head long, snout somewhat depressed, postorbital portion about six time as long as snout. Dorsal and anal fin nearly equal in length, on last quarter of body, caudal fin rounded. Head green, scales large, bluish-green in forepart of body, getting red toward the rear end, crimson on caudal peduncle.
Size observed: up to 4 m or more, up to 200 kg, usually 2-2.5 m, 90 kg.
Taxonomic description
-Body elongate, round in cross-section, outlines of back and belly straigth, running nearly parallel to each other.
-Head long, upper profile somewhat depressed, duck-like.
-Snout short, about 1/6 of postorbital length.
-Mouth supraterminal, its edge not extending to anterior rim of eye.
-Eye rather small.
-Opercle smooth, opercular cleft round, semicircular, its upper edge close to back side of the head.
-Origin of pectoral fin close to lower end of opercular cleft, fin rather short.
-Pelvic abdominal, short, originating posterior to middle of body, much closer to anal than to pectoral fin.
-Dorsal and anal fins nearly equal in length of both base and fin-rays, dorsal originating slightly anterior to anal, ending nearly above end of anal.
-Caudal fin on short peduncle, with rounded border. Scales quite large, but all of nearly equal size, lateral line scales inclusive.
-Coloration, forepart of body bluish green on silvery ground, darkest on the head, scales changing from blue-green to reddish towards the tail region, with red border, caudal peduncle crimson.
Males during spawing season and brood care with glandular fields on the upper side of the head, the milky secretion most probably is a pheromone to keep the juvenile close to the parent.
Type locality
Not known.
Distribution
Freshwater of tropical South-America, Amazon and Orinoco basins, Brazil, the Guayanas, Peru.