(Forsskål)
1. Distinctive characteristics of early developmental stages
(a) Eggs and larvae
Not yet recorded from the mangroves.
(b) Early juveniles (Based on 49 mm T.L. specimens)
Gnathanodon speciosus 1
Eyes without adipose tissue. Four broad vertical bands are present on the body and extend from the dorsal to the ventral profile, crossing the lateral line. Another mild band runs obliquely above the eye. Narrow vertical bands (usually alternating with the broader bands in advanced juveniles and small adults/young adults) are yet to develop at this early juvenile stage. The bands are more prominent in formalin-preserved specimens than those of fresh ones. The dark opercular spot (which is present in juveniles and adults) has not yet formed, but is present as a pigmented blotch covering over half the opercular region at this stage. Teeth lacking (at least up to 10 cm size).
The third spine of the first spinous dorsal fin is the longest. The second dorsal lobe is not fully developed. The height of the longest ray of the second dorsal is less than that of the longest spine of the first dorsal (usually vice-versa in adults). The pectoral fins and lobes of the second dorsal and anal fin are relatively smaller in proportion to the body size in early juveniles, when compared with adults. The eyes are relatively larger in proportion in early juveniles than in adults.
The junction between the curved and straight portion of the lateral line lies below the 7th ray of the second dorsal fin (usually between the 9th and 14th rays in adults). The scales and scutes in the straight part of the lateral line are not distinguishable at this stage.
2. Distinguishing characteristics of similar species occurring in the mangroves (after Smith-Vaniz, 1984; Smith, 1968; Gomez, 1980)
(a) Juveniles of Carangoides caeruleopinnatus
The upper margin of the operculum has a black spot but there is no vertical band on the body. Adipose eyelids are also absent. The lower arm of the gill arch has 15-17 rakers (19 to 22 gill rakers in the lower arm of the gill arch of the Gnathanodon speciosus ) (Reported from the Philippine mangroves)
(b) Juveniles of Carangoides dinema
A brown and diffused opercular blotch is present. The body has no bands. A row of small blotches (usually 13 in number) are present between the base of the dorsal fin rays and the size of the blotches gradually increases towards posterior side lobe of the second dorsal fin which is elongated. (Reported from the Philippine mangroves).
(c) Early juveniles of Carangoides praeustus
(vide Carangoides praeustus on this CD-ROM)
(d) Juveniles of Caranx ignobilis
The body is silvery and the fins are yellow in colour. The lower arm of the first gill arch has 15-17 gill raker processes. Bands are absent on the body and the posterior part of the eyes possess moderately developed adipose eyelids.
(e) Juveniles of Caranx papuensis
A conspicuous pale spot is present on the shoulder just behind the postera-dorsal margin of the operculum. (Reported from the Philippine mangroves).
(f) Juveniles of Caranx sem
The upper lobe of the caudal fin and the second dorsal is darkly pigmented. The lower arm of first gill arch has 17 to 19 gill rakers. No distinct bands are observed. Adipose eyelids moderately developed in the posterior part of eyes.
3. Distinguishing characteristics of similar species occurring in the inshore waters (largely after Smith-Vaniz, 1984; Delsman, 1926a; Munro, 1955)
(a) Early juveniles of Carangoides armatus
One vertical band emerges from upper part of the eye towards the spinous dorsal fin. Six more vertical bands are present on the body covering the entire depth, of which two are located in the narrow caudal peduncle (both depth-wise and length-wise). The body depth is very high in proportion to the total length/fork-length in early juveniles when compared to that of adults. The pectoral fin shape is broader than longer and has a rounded tip in early juveniles (whilst it is longer than broader and sickle-shaped in fully grown fish). The elongated second dorsal lobe and the anal fin lobe are filamentous and even reaches the body length in early juveniles (while the filaments in adults are only about 1-1.5 times longer than the head length). The rays located at the middle portion of the second dorsal and anal fin are not filamentous in any juveniles, while they are filamentous in adult males which exhibit sexual dimorphism (the second dorsal and anal fin lobes are not filamentous in the case of the Gnathanodon specious).
(b) Juveniles of Carangodes ferdau
Five to seven dusky bands are present on the sides of the body. No band is present near the eye. An opercular spot is absent. Feebly visible golden spots are at times present and scattered dorsally above the lateral line. The lower arm is situated dorsally above the lateral line. The lower arm of the first gill arch has 17-20 gill rakers. The outer row of the upper jaw has no canine teeth.
(c) Juveniles of Caranx tiffe
The upper margin of the operculum has a black spot but vertical bands in the body are absent. An adipose eyelid is present.
(d) Juveniles of Caranx para
A black spot is present on the upper margin of the operculum. Seven cross bars are at times present but confined to only above the lateral line. The ventral profile of the body is strongly curved.
(e) Juveniles of Selar malam
A shoulder spot is present on the upper margin of the operculum. Around 6-9 cross bars are present on the body above the lateral line. The ventral profile of the body is not as curved as that of the Caranx para. The lobe of the second dorsal and lobes of the caudal fin are at times highly pigmented.
4. Distinguishing characteristics of similar species occurring in the offshore/oceanic waters of the Indo-pacific (largely after Smith-Vaniz, 1984)
(a) Juveniles of Naucrates ductor
Five bands are present on the body. The membranous first spinous dorsal is absent. Instead, four or five small spines are embedded prior to the soft dorsal. Scutes are absent in the lateral line. Instead, a lateral flesh keel is present in the caudal peduncle along the lateral line.
(b) Juveniles of Seriola rivoliana
A dark nuchal bar is present, emerging from the eye towards the spinous dorsal. The body has six more dark bars. The lateral line is devoid of any scutes or anchored scales.
5. Salient biological characteristics (after Smith-Vaniz, 1984)
Maximum length and weight recorded: 1100 mm (fork length) and 14.8 kg respectively. It feeds on crustaceans, molluscs and fish.
6. Salient ecological information (after Smith-Vaniz, 1984)
Gnathanodon speciosus is widely distributed throughout the Indo-Pacific region, including the East coast of Africa, the Red Sea, the Gulf, India, Southeast Asian Coasts, Japan, the northern part of Australia, Hawaii and the West coast of America between California and Peru. It occurs in coastal waters including rocky and seaward reefs and deep lagoons. The early juveniles and juveniles rarely visit the mangroves located adjacently to the reefs when neritic conditions prevail in the lower reaches. The young fish are reported to exhibit an association with sharks and serranids through ‘piloting behaviour’.
7. Capture fisheries
Spear fishing and gill-netting are in practice to capture this species from the coastal environment. In the mangroves, the juveniles are sporadically caught in cast-nets and drag-nets.