(Bleeker)
1. Distinctive characteristics of early developmental stages
(a) Eggs and larvae
No information from the mangroves.
(b) Early juveniles
Gerres abbreviatus 1
The mouth is protractile. The nuchal crest is absent. The dorsal fin has 9 spines and 10-11 rays. The second dorsal fin spine is about half the depth of body. The body depth and the pectoral fin length are proportionately small at this stage when compared to adults. On the other hand, the head length is proportionately larger in early juveniles than in adults. There are seven vertical bands on the upper half of the body, of which a few cross the lateral line. The spinous dorsal fin has black pigment on the upper margin while the soft dorsal fin has black pigment in the form of a band near the basal region. Apart from that, the caudal peduncle, caudal fin base and anal fin base have distinct pigmentation.
2. Distinguishing characteristics of early developmental stages in similar species occurring in the brackish water (including the mangroves) and the marine environment
(a) Larvae of Gerres lucidus
Gerres lucidus 1 (Courtesy of Dr. A. Termvidchakorn, Thailand)
The dorsal profile has four pigmentation patches which become four diffused dark saddles along the upper half of the body in adults.
(b) Eggs, larvae and early juveniles of Gerres oblongus (after Bensam, 1983)
Gerres oblongus 1; Gerres oblongus 2; Gerres oblongus 3
The eggs are spherical and are 0.63-0.73 mm in diameter. The yolk is vacuolated. The perivitelline space is narrow and a black pigmented oil globule measuring about 0.2 mm in diameter is present. The 6 mm larva has 7 pre-anal and 17 post-anal myomeres. In early juveniles, the first dorsal fin has 9 spines only. The anal fin has 3 spines and 7 soft rays. The mouth is protractile.
(c) Early juveniles of Gerres oyena
Seven or eight vertical bands are present on the body. The tip of the spinous part of the dorsal fin is highly pigmented to form a black blotch. The upper portion of both the spinous and soft dorsal fin is lined with pigmentation (the upper portion of the spinous dorsal and lower portion of the soft dorsal fin is lined with pigmentation in G. abbreviates ).
(d) Larvae and early juveniles of Gerreomorpha setifer (after Bensam, 1983)
Gerreomorpha setifer 1; Gerreomorpha setifer 2
The spinous dorsal fin has 10 spines (instead of 9 in many species of the silver-biddies).
3. Salient biological characteristics (after Fischer and Bianchi, 1984; Jeyaseelan, 1981)
This species grows to a maximum size of 250 mm in length. Juveniles were reported to feed on zooplankton, while adults on small polychaetes, bivalves, crustaceans and fish. In the mangrove waters, the gut contents of young fish showed the presence of detritus, small molluscs, polychaetes and crustacean appendages.
4. Salient ecological information (after Fischer and Bianchi, 1984; Jeyaseelan, 1981)
It is a coastal species whose juveniles and young adults frequently enter the brackish waters, including the mangroves. Young ones are reported to dwell in the littoral zone, while the adults occur up to 40 m depth in the inshore waters. This fish is a school-forming species reported to live on sandy bottoms. Juveniles in the mangroves also occur on the muddy bottom. The protractile mouth helps in capturing the prey from the benthic environment.
5. Capture fisheries
This species is caught by bottom trawls, seines and traps from inshore waters. In the mangrove waters destructive fishing of undersized groups is carried out by cast-nets and drag-nets. In brackish water lakes and estuaries, this species constitutes a considerable fishery among fin fishes.