(Schneider)
1. Distinctive characters of early developmental stages
(a) Eggs
Thryssa mystax 1
Eggs are pelagic, imperfectly spherical with 0.8 to 0.85 mm diameter, colourless and with narrow perivitelline space; yolk coarsely segmented; oil globule absent; early stage of egg is with unsegmented germinal disc; the 12 hour old embryo possesses 16 somites, whereas 17 hours old embryo has 28 somites. The embryo is devoid of pigments even in eyes. Tail of the embryo is free from the yolk mass in advanced stage.
(b) Larvae
Thryssa mystax 2
Early larval stages have net yet been recorded from the brackish water mangroves. Postlarva measuring over 18 mm length possesses 27 pre-anal and 18 post anal myomeres. Advanced larva has a wide and inferior mouth. Maxillary bones with minute conical teeth cross beyond the eye, but yet to reach beyond the operculum. Pectoral fins membranous, semi-circular and possess rays. Pelvic rays fully formed and are seven in number. Dorsal fin with 15 rays situated behind the middle of the body move forward and reaches the middle as the larva grows. Anal fin with over 35 rays and forked caudal fin with 25 rays. About 5 pigment spots are present near foregut, 3 branching chromatophores above mid gut and 4 at the base of the anal fin. Few streaks of pigments are present at the base of the caudal lobe and also in the dorsal fin.
(c) Juveniles
Maxilla long, reaching up to pectoral base; gill raker serrae uneven and not clumped; lower gill rakers 14-17; Anal with 35-41 rays; dorsal with 13-16 rays; mouth nearly horizontal; prepelvic scutes17-19; post pelvic scutes 10-12.
2. Distinctive characters of early developmental stages in similar species occurring in the mangroves
(a) Eggs of Thryssa hamiltonii
Relatively bigger in size (1.1 to 1.27 mm in diameter).
(b) Larvae of Thryssa hamiltonii
Pre-anal myomere count is 30 (28 in the case of Thryssa mystax ).
3. Salient biological (including ecological) information
This species is reported to spawn during September- May in Indian waters (Venkataraman, 1956). It has at least two spawning seasons and attains a maximum size of 200 mm in coastal waters. Specimens with 35-150 mm size groups commonly occur in mangroves. This species dwells in coastal pelagic region and often enters the mangroves and adjacent brackish waters. Though the eggs and larvae are recorded in lower reaches of mangroves where neritic conditions prevail, the juveniles and adults penetrate to the upper reaches where mixo-mesohaline conditions prevail. The young ones of this species occur even in moderate turbid waters (with up to 400 g/m^3 seston content) in the mangrove waterways (Jeyaseelan, 1981). Of the six species of juvenile and adult Thryssa reported from the mangrove waterways of south east coast of India, this species is the most common one. This species is distributed in the Indo-Pacific from Indian coasts through Thailand, Singapore, Indonesia and up to Taiwan in the North and Papua New Guinea and Queensland in the south. The juveniles in the mangroves feed on mysids, sergestids, postlarval stages of shrimp and fish larvae (Jeyaseelan, 1981). It feeds on planktonic organisms in the coastal waters.