(Cuvier)
1. Distinctive characteristics of early developmental stages
(a) Eggs and larvae
Not reported from the mangroves.
(b) Early juveniles (description based on 35 mm T.L. specimens)
Scomberoides tala 1
The lateral line has no scutes. Preoperculum spines are absent at this stage. The spinous dorsal fin has one forward pointing (antrorse) spine (which becomes embedded with age) and seven upward pointing spines which are depressible into a shallow groove on the dorsal mid-line. The dorsal spines are well connected by membranes and are proportionately greater in height than in adults and not embedded in the body at this early juvenile stage (these first dorsal fin spines become shorter and separate without a membrane in adults). The second dorsal and anal fins have one spine each and 20 and 18 rays respectively, and the anal fin has 2 detached spines of which the posterior one is longer and stronger. The anteriorly located rays in the 2nd dorsal and anal fins are somewhat raised in comparison to the posterior ones to form future lobes in fully grown specimens. The future lobes of the 2nd dorsal and anal fins are devoid of any pigmentation at this stage (whereas they are highly pigmented in fully grown specimens).
The posterior part of the 2nd dorsal and anal fin rays are yet to transform as semi-detachable finlets (adults possess semi-detachable finlets). The upper jaw has not yet extended beyond the posterior part of the eye (in adults, the upper jaw extends beyond the posterior margin of the eye). Twelve gill rakers are countable in total in the first gill arch excluding the rudiments (by using a dissection microscope). Vertically elongated blotches are absent on the sides of the body (usually 4-8 vertically elongated blotches are present in adults – most of them intersecting the lateral line). The caudal fin is not yet strongly forked in early juveniles. The eyes are proportionately bigger in young ones than in adults. Pigmentation in the form of three small rings is present in the angle between the pectoral and pelvic fins.
2. Distinguishing characteristics of early developmental stages in similar species occurring in the mangroves (after Smith-Vaniz, 1984; Agate et al., 1991; Gomez, 1980; Jeyaseelan, 1981)
(a) Juveniles of Scomberoides commersonianus
The upper jaw extends well beyond the posterior margin of the eye (not so in S. tol).
(b) Early juveniles and juveniles of Scomberoides lysan and S. tol.
There are more gill rakers (21-26 in total) in the first gill arch (in S. tol the total number of gill rakers, excluding the rudiments in the first gill arch, is between 11-15). The antrorse spine absent in juveniles.
Scomberoides tol 1
Early juvenile of S. tol (29 mm T.L.) (after Venkataramanujam, 1975)
3. Salient biological characteristics
Maximum size recorded: 620 mm fork length. Little information is available about the biology of this species. It is a carnivore, especially a piscivore, leading a nektonic life.
4. Salient ecological information
It is an inshore species whose early juveniles and juveniles rarely visit the mangrove waters to obtain food and protection. The early juveniles are recorded from the mangroves of Thailand during the wet season. It is distributed throughout the Sri Lankan coast, the East coast of India, the Indo Malayan Archipelago and up to the Philippines (in the northern limit) and up to Northern Australia (in the southern limit).