(Forsskål)
1. Distinctive characteristics of early developmental stages
(a) Eggs and larvae
Nothing is known.
(b) Early juveniles/juveniles (Based on 39 mm (T.L.) specimens and above)
Lethrinus nebulosus 1
The head length is almost equal to the body depth. The head profile has a slight hump above the orbit. There are seven undistinct vertical cross bars present in the upper half of the body. The vertical cross bars are continuous and not yet broken into blotches at this stage. Streaks (radiating from the eye) are totally absent. There are no red markings at the base of the pectoral fin, on the preoperculum and opercular margin nor between the eye or middle of the upper jaw. There is no blotch below the lateral line opposite to the tip of the pectoral, but there is a quadrangular blotch between the lateral line and the middle of the pectoral fin (in other words, the blotch is located posteriorly to the opercular margin). The preoperculum region is darkly pigmented and serrations are present at times at the anterior portion of the vertical rim of the preoperculum in early juveniles.
The pectoral fin is relatively short in proportion with those in adults. The dorsal fin has 10 spines and 9 soft rays. Among the spines in the dorsal fin, the first one is the shortest, whilst the third one is the longest. The anal fin has 3 spines and branched rays.
2. Distinguishing characteristics of early stages of the species from those of adults
The body depth is greater than the head length in adults (almost equal to the head length in early juveniles and more than the head length in young adults). Two or three blue streaks radiate from the eye in adults (juveniles have no streaks radiating from the eye). White or blue spots are present on the back of each scale in adults (not so in early juveniles and juveniles). The colouration is olive green above and paler below in adults (brownish- pink above and paler below in juveniles). There is no quadrangular black blotch between the lateral line and the middle position of the pectoral fin in adults (a black blotch is present in early juveniles and juveniles).
3. Distinguishing characteristics of early stages in similar species occurring in the mangroves
(a) Juveniles of Lethrinus harak
A large black oblong blotch with a golden yellow rim is present on the side of body (not so in L. nebulosus ). (L. harak is reported from the mangroves of Asia Pacific (Rao, 1986).)
(b) Juveniles of Lethrinus nematacanthus
A second dorsal is produced (not so in L. nebulosus ). (L. pematacanthus is reported from the mangroves of the Philippines (Guerrero and Guerrero, 1975).)
(c) Juveniles of Lethrinus reticulatus / Lethrinus semicinctus (after Sato, 1978; Fischer and Bianchi, 1984)
Seven or eight vertical cross bars are present in both the species as in the case of the juvenile L. nebulosus. A dark irregular blotch is present below the lateral line opposite to pectoral fin in L. semicinctus (not so in juvenile L. nebulosus ). Characteristic red/pink markings are present at the base of the pectoral fin, at the posterior end of the operculum, along the preoperculum, from the eye to the middle of the upper jaw and from the eye to the occipital region in L. reticulatus (not so in juveniles of L. nebulosus ). (L. reticulatus was reported from the mangroves of Asia Pacific (Rao, 1986). L. reticulatus was previously considered as a valid species (Sato, 1978). However, of late, L. reticulatus Valenciennes 1830 was reported as a doubtful species and L. reticulatus non Valenciennes 1830 was synonymised as L. semicinctus Valenciennes 1830, vide Fischer and Bianchi, 1984.)
(d) Juveniles of Lethrinus variegatus
A reticulated pattern is present on the body. In addition, two dark bands originating from the eye are reported from young fish. Of these two bands from the eye, one runs straight downwards and the other to the middle of the upper jaw (Sato, 1978). (This species is reported from the mangroves of Asia Pacific, vide Rao, 1986.)
4. Distinguishing characteristics of early stages in similar species occurring in the coastal/coral reef environment
(a) Juveniles of Lethrinus rubrioperculatus
A characteristic red spot is present on the posterior end of the operculum and at the base of the pectoral fin. The caudal fin is lunate and the upper lobe of is longer than the lower lobe.
(b) Juveniles of Lethrinus xanthochilus
Body markings are similar to juvenile L. nebulosus but a red spot is present at the pectoral fin (a red spot is absent at the base of the pectoral in L. nebulosus juveniles).
5. Salient biological characteristics
The juveniles of this species feed on small crabs and hermit crabs in the mangrove waters of the southeast Indian region (Jeyaseelan, 1981). Based on the recruitment of early juveniles and juveniles in the mangroves, this species seems to spawn during February-May and August-September in the adjacent seas/coral environment.
6. Salient ecological information
Early juveniles and juveniles of this species occur in the lower reaches of the mangrove waters during the summer, the early southwest monsoon and the middle of the northeast monsoon seasons. The minimum and maximum size (in total length) recorded in the mangrove waters were 39 mm and 136 mm respectively. The juveniles were recorded in mangrove waters with salinity as low as 15 ppt during the northeast monsoon season from the southeast coast of India. It is also reported from the mangrove waters of Taiwan (Burgess and Axelrod, 1991) and Singapore (Gomez, 1980).
7. Capture fisheries
The adults of this species seem to inhabit deeper waters off the southwest coast of India and were caught with experimental long lines and deep sea trawling.