(Forsskål, 1775)
1. Distinctive characteristics of early developmental stages
(a) Eggs and pro-larvae (Not from the mangroves)
Terapon jarbua 1; Terapon jarbua 2
The eggs are pelagic and spherical and measure around 0.75 mm in diameter. A large oil globule measuring about 0.45 mm in diameter is present. Eggs often aggregate with planktonic cladocerans. The perivitelline space is narrow. The yolk has no segments, no vacuoles and no pigment. The yolk and oil globule have a glistening appearance and the oil globule is highly pigmented with a stellate and branching melanophores. The eggs hatch in about 10 hours. The pro-larvae measure about 1.6 mm in length, are oval in shape and are sturdy. The larvae are excessively pigmented with a light-greenish pigment all over the body excluding the larval finfolds. Along the base of the finfold, in the dorsal profile, a series of black pigments are present. The pro-larvae have 18 pre-anal and post-anal countable myomeres amidst heavy pigmentation.
(b) Advanced post-larvae and early juveniles
Terapon jarbua 3
Post-larvae measuring 12 mm total in length have 6 spines in the opercular region of which the one located at the top of the opercular margin is long and strong (which is the one remaining even in adults). Of the remaining 5 small spines, three are located at the angular edge of the lower operculum and two are located in front of the bordering spines. In early juveniles measuring over 25 mm, these small spines disappear and only one small spine is located below the preoperculum serrations (in adults, the single preoperculum spine also disappears and the serrations alone remain).
There is no apparent variation in the number of spines and rays in respective fins among advanced post-larvae, early juveniles and adults. However, the height of the anal spines vary among these life history stages. In the post-larvae, among the three anal spines, the second one is the longest. In the early juveniles, the first anal spine is short, whilst the 2nd and 3rd spines are almost equal in length (in adults, the first anal spine is the shortest, while the third one is the longest). Regarding pigmentation, the longitudinal strips have not yet formed in the body of post-larvae; instead, black stellate chromatopores are spread all over the body and head. In early juveniles, three blackish-brown downwardly curved longitudinal stripes are formed (and persist even in adults).
In the post-larvae, the upper half of the dorsal spines between the 2nd and 8th spines are deeply pigmented. In early juveniles, the pigmentation in the dorsal spines is restricted between the 2nd and 6th spines, whilst in adults, it transforms into a distinct blackish band or blotch of a bigger size in the upper part of the membrane between the 3rd and 6th spine, and a smaller one between the 7th and 9th spine.
In the soft dorsal, the pigmentation is restricted to the lower portion of the fin in the post-larvae, while it moves upwards in early juveniles. In adults, black pigments occupy the tip of the first three dorsal rays, the entire portion between the 5th and 8th ray and the last two rays.
In the caudal fin there is pigmentation in the median rays. The tip of the caudal lobes and transverse bands (between the median rays and caudal tips) are absent in the post-larvae, while they are formed as 5 distinct bands in the early juveniles and remain intact in adults.
2. Distinguishing characteristics of early developmental stages in related species occurring in the mangroves
(a) Early juveniles of Terapon puta (videTerapon puta 1)
The body is somewhat elongated (body depth is relatively more in T. jarbua ). Longitudinal stripes in the body are straight (curved downward in T. jarbua ). In fresh specimens, pearly spot-like structures are at times feebly visible throughout the body. The body is somewhat greenish, dorsally, in specimens obtained from sea grass beds, at the lower reaches of the mangroves (body is brownish/greyish dorsally in T. jarbua ).
(b) Post-larvae of Palates quadrilineatus
Palates quadrilineatus 1
The area behind the pectoral fin in the body is highly pigmented, which moves towards the shoulder in juveniles and adults to form a distinct blotch (not so in T. jarbua ). The head is not relatively shorter (thus ruling out its identity as the post-larvae of Helotes sexlineatus which also possess a blotch at the shoulder). The spinous dorsal fin is fully pigmented. The pre-anal and post-anal myomere counts are 12 and 13 respectively (post-larvae of P. quadrilineatus were recorded from the Thailand mangroves).
(c) Early juveniles of Pelates quadrilineatus
A blotch is present on the shoulder. The caudal fin is without bands or stripes. The gill membrane is joined to the isthmus (whereas it is free from the isthmus in the Terapon spp). A maximum of 5 or 6 horizontal and straight stripes are present in the body.
3. Distinguishing characteristics of early developmental stages in related species occurring in the adjacent coastal waters
(a) Early juveniles of Terapon theraps
Dark brown horizontal stripes in the body are straight (curved down in T. jarbua ). It is a coastal species and juveniles rarely enter the mangroves and brackish waters.
(b) Early juveniles of Helotes sexlineatus
A blotch is present on the shoulder. The head is relatively short. Teeth, if well developed, have three cusps (conical in T. jarbua ).
4. Salient biological characteristics
This species grows to a maximum size of 300 mm in coastal waters (Fischer and Bianchi, 1984). It breeds in inshore waters. The advanced post-larvae and early juveniles enter the mangroves and brackish waters. At around 10 cm in length this species generally completes the nursery phase and enters the coastal waters for further growth and reproduction. Based on the recruitment of the early developmental stages and young fish in the mangrove waters of the Southeast Indian coast, this species seems to breed round the year in inshore waters with a brief pause during July-August. However, from year to year variations in spawning periodicity are not uncommon. The juveniles feed on sergestids, shrimp juveniles, gammarids, crab zoea, tanaids and species of corophidae in descending order of importance in the Southeast Indian mangroves (Jeyaseelan, 1981).
5. Salient ecological information
It is a coastal species, whose juveniles dwell commonly in brackish waters and mangroves. It penetrates even up to freshwater. It is a 'scale eater' – a habit probably associated with Acanthocephalan parasitism in the mangroves (Fischer and Bianchi, 1984 and Jeyaseelan, 1981). The young fish form small schools (of less than 20 individuals per school) and browse actively in the supra littoral zones of the mangroves and brackish waters during high tides. This species is widely distributed throughout the Indo-Pacific region.
6. Capture fisheries
It is caught by handlines, gill-nets, shore seines and trawls. It could be made economically important through the introduction in coastal resorts/picnic spots of small scale sport fishing. This hardy fish produces soundly in living conditions even when out of water.
7. Culture fisheries
It is an attractive and sturdy fish with brilliant markings on the body and it could be useful for brackish water and even freshwater aquariculture.