(Pallas)
1. Distinctive characteristics of early developmental stages
(a) Eggs (after Thangaraja, 1982 and Manickasundaram, 1990)
Callionymus sagitta 1
The eggs are pelagic, spherical in shape, transparent, and measure between 0.52-0.7 mm in diameter. The perivitelline space is narrow. The egg membrane has hexagonal (honeycomb-like) ridges on the surface. The unfragmented yolk has no oil globule.
(b) Larvae
Callionymus sagitta 2 (Courtesy: A. Termvidchakorn, Thailand)
The early post larva possesses 26 myomeres of which 11 are pre-anal and the rest are post-anal in position (more than 24 myomeres in this tropical species). The pectoral fin is enlarged. There is no crest on the nape. In 3 mm long larva, the lower lobe of the caudal fin is irregular in shape. The body is laterally compressed (not dorsoventrally flattened at this stage). Pigmentation is prominent along the mid-lateral line from the post-orbital region and also in the breast. A pigmented band passes along the ventral portion of the operculum up to the posterior tip of the pectoral fin and borders the ventral side of the myomeres.
Callionymus sagitta 3
In advanced post-larvae measuring over 9 mm, the body is somewhat dorsoventrally flattened and at times cylindrical. The head is prominently depressed dorsoventrally. The caudal fin is almost oval in shape. The dorsal region of the body has 4-5 bands of pigment. The first dorsal has 4 spines and the second dorsal has 9-10 rays. The typical preoperculum process with a slight forward-directed spine and strong posteriorly-directed spine with 4 lateral processes are discernible.
2. Distinguishing characteristics of early developmental stages in similar species occurring in the mangroves and adjacent seas
(a) Eggs of Synodontidae
A hexagonal egg membrane is present in many of the synodontids, but the eggs are generally larger than that of C. sagitta . The perivitelline space is wide (in the case of C. sagitta the perivitelline space is very narrow).
(b) Larvae of Platycephalus spp.
The first dorsal fin has one isolated spine followed by 7-8 spines (in the case of C. sagitta , only 4 spines are present in the first dorsal). The preoperculum region does not possess a strong posteriorly-directed spine (the preoperculum process possesses a posteriorly-directed spine with 4 to 5 processes in the case of C. sagitta ).
(c) Post-larvae and early juveniles of Callionymus jonesii
Only 3 spines in the first dorsal (4 spines in the case of C. sagitta ).
3. Salient biological and ecological information
Little is known about this species. It grows to a maximum size of 11 cm in total length. Both early developmental stages and adults occur in the mangroves but in a less frequent manner. It does not constitute a commercial fishery and is a demersal fish.