Morphology Data of Oreochromis aureus
Identification keys
Main Ref. Trewavas, E., 1983
Appearance refers to Male; Female
Bones in OsteoBase

Sex attributes

Specialized organs no special organs
Different appearance always different morphology between mature adults
Different colors different colors during breeding season only
Remarks Males grow remarkably larger than females and possess much better developed finnage (Ref. 52307). Soft rays of dorsal and anal fin are longer in mature males (Ref. 2), and sometimes the vermillion margin of the dorsal fin is thickened with reduced (but not closed) notches (Ref. 2, 54504). Pelvic fins of males usually longer than those of females, reaching anus or genital papilla, and this difference is more pronounced in larger specimens; dorsal and anal fins pointed in males and rounded in females (Ref. 54504). Standard length and snout length are larger in males, while iris diameter, head length, predorsal length, prepelvic and preanal length are smaller in males (Ref. 54458). Males with one urogenital opening, females with 2 separate urinary and genital pores (Ref. 54504).

Descriptive characteristics of juvenile and adult

Striking features none
Body shape lateral fusiform / normal
Cross section
Dorsal head profile more or less straight
Type of eyes more or less normal
Type of mouth/snout more or less normal
Position of mouth terminal
Type of scales cycloid scales

Diagnosis: Adults: narrow preorbital bone (depth max. 21.5% of head length in fishes up to 21.3cm SL); lower pharyngeal jaw with short blade; no enlargement of the jaws in mature fish (lower jaw not exceeding and usually less than 36.8% head length) (Ref. 2). Caudal without regular dark vertical stripes (Ref. 2, 53405, 54467), but with a broad pink to bright red distal margin (Ref. 2). Breeding males assume an intense bright metallic blue on the head, a vermilion edge to the dorsal fin and a more intense pink on the caudal margin (Ref. 2, 54467). Breeding females with the edges of dorsal and caudal fins in a paler more orange color (Ref. 2). Juveniles: upper line of head profile running upward from snout at sharp angle; lower pharyngeal bone nearly triangular, teeth numerous but not densely crowded; dorsal and anal fin striped, with stripes running obliquely on the soft dorsal and longitudinally on the caudal fin; black Tilapia-mark on soft dorsal present; body dark; lower lip developed from beneath (Ref. 54566).

Description: deep bodied; teeth very small, typical for an algae feeder (Ref. 52307), in 3-5 rows in the jaws, bicuspid in the outermost (Ref. 2, 53405, 54467), tricuspid in the others (Ref. 2, 54467). Lower pharyngeal bone with bicuspid teeth, its toothed part as long as anterior part (Ref. 53405). Scales cycloid (Ref. 367, 2756, 54408), with fringes of the embedded part almost straight (Ref. 54408). Scales on cheek in 2-3 horizontal series; 5-7 scales between base of pectoral and pelvic fin (Ref. 2, 54467). 13.5-14.5 scales below upper lateral line before the pelvic fins (Ref. 367). 2 scales between upper and lower lateral line (Ref. 367, 2756). Upper lateral line with 20-23 scales, lower with 14-18 scales (Ref. 367, 2756). Microbranchiospines present on outer sides of arches 2 to 4 (Ref. 2). Dorsal fin edge thickened and notches between lappets closed in fully ripe males (Ref. 364, 54467). Last dorsal spine the longest (Ref. 367, 2756). Third anal spine a little shorter than last dorsal spine (Ref. 2, 2756, 54467), but stronger (Ref. 2, 54467). Pelvics not greatly produced; caudal often with rounded corners, usually scaly only at the base and between rays on upper and lower parts of the fin; genital papilla of mature male conical or with narrow bifid flange (Ref. 2, 54467).

Coloration: Juveniles: grey-brown to slightly golden (Ref. 52307), with vertical bars on sides (Ref. 53405). Specimens <10cm with well developed "Tilapia"-spot on soft dorsal fin (Ref. 2, 52307, 53405, 54467). Sometimes with vague vertical bars on caudal fin (Ref. 2, 3032). Adults: eye with red iris crossed by a black bar (Ref. 2). Ventral region pale silvery-grey (Ref. 2, 367, 3032, 52307). Lips often blackish (Ref. 367). Chin and chest may be blue-black (Ref. 2, 6465). Throat and belly sometimes yellowish but never reddish (Ref. 2756). Silvery and dark spots distributed all over the body (Ref. 52307). Sometimes with several vertical bars on body (Ref. 2, 3032, 31256, 52307), related to emotional state (Ref. 53405, 54467). Opercular spot generally present (Ref. 367, 2756, 54759), but may become totally invisible (Ref. 367). Pectoral fins greyish, pelvic fins blackish (Ref. 367, 2756). Dorsal fin (Ref. 2, 2756, 3032, 52307, 54467) and upper parts of caudal fin (Ref. 2, 367, 2756, 3023, 3032, 6465, 13851, 51850, 52307, 53405) with red margins. Soft dorsal and anal fin, and normally also the caudal fin, with numerous pale spots (Ref. 2, 2756, 3032, 31256, 52307, 54467, 54759). Spots on dorsal and anal fin in oblique rows (Ref. 367). Dorsal fin lappets dark, never red or pale (Ref. 51850). Adult males grey-blue, with head, from upper lips to eye, greenish-brown, becoming darker towards the back; courting males brilliant with metallic blue sparkles on the head (Ref. 52307), or intense metallic blue on the head, sometimes paler blue on the body, with a vermillion edge on the dorsal and a more intense pink caudal margin (Ref. 2, 6465, 54467). Breeding females with paler, more orange edges of dorsal and caudal fin (Ref. 2, 6465). Preserved specimens sometimes with black lateral band (Ref. 53405).

Ease of Identification likely to be confused with closely related species.

Meristic characteristics of Oreochromis aureus

Lateral Lines 2 Interrupted: No
Scales on lateral line 29 - 33
Pored lateral line scales
Scales in lateral series
Scale rows above lateral line 4 - 5.5
Scale rows below lateral line
Scales around caudal peduncle
Barbels 0
Gill clefts (sharks/rays only) absent
Gill rakers
on lower limb 18 - 30
on upper limb 5 - 8
total 28 - 31


Dorsal fin(s)

Attributes extending over most of the back length
Fins number 1
Finlets No. Dorsal   0
Ventral  0
Spines total 14 - 17
Soft-rays total 11 - 15
Adipose fin absent

Caudal fin

Attributes more or less truncate; more or less normal

Anal fin(s)

Fins number 1
Spines total 3 - 3
Soft-rays total 8 - 11

Paired fins

Pectoral Attributes  more or less normal
Soft-rays   13 - 16
Pelvics Attributes  more or less normal
Position    thoracic  beneath origin of D1
Spines     1
Soft-rays   5 - 5
Main Ref. (e.g. 9948)
Glossary ( e.g. cephalopods )
Entered by Binohlan, Crispina B.
Modified by Musschoot, Tobias
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