Abstract:This study described the developmental characteristics of external apparatus during early life stages of bluefin leatherjacket, Thamnaconus modestus. The developmental morphological characteristics of 11 external apparatus were recorded and described in detail. 1) Mouth: opened at 2-3 dph(days post hatching), then grew continuously except at the stagnation stage (24-28 dph). 2) Eyes: pigment appeared at 1 dph, choroids formed and the pupil was black at 3 dph, sclera formed at 4 dph, rim of the eye appeared at 14 dph, and the eye form was same with adults at 40 dph basically. 3) First dorsal fin spine: anlage appeared at 3 dph, fin spine formed initially at 7-8 dph, protruded out of body at 10 dph, development finished roughly at 14 dph, and the shape was the same with adult at 60 dph basically. 4) Girdles and pelvic fin spine: Girdles appeared at 5 dph, pelvic fin spine grew fast at 5-7 dph, and shunk from 10 dph, all pelvic fin spine off at 30 dph. The shape of girdles was the same with adult at 60 dph. 5) Pectoral fin: fin membrane thickened and the fin ray formed at 15 dph, developed completely at 30 dph. 6) Dorsal fin and anal fin: fin suspensorium and fin ray appeared at 14 dph, fin ray developed completely at 24 dph, and the shape at 60 dph was the same with adult’s. 7) Caudal peduncle: caudal vertebra was straight until 14dph, some fin ray anlage appeared under the tail end of notochord at 16 dph. The tail end of notochord up-curved, fin ray developed completely and sub-section at 16-24 dph. Caudal fin turned into rotundity at 50 dph. 8) Scales and skin: epidermis thickened at 8dph, the compact epidermis appeared first at head, full body covered by scales at 40dph, turned into withy leathery epidermis. 9) Abdomen and splanchnic zone: yolk-sac was absorbed, anus and the first intestinal loop formed at 2 dph, oil ball disappeared and the fish larvae fed on the oyster larvae. The anlages of liver, kidney and swim bladder appeared at 8-12 dph, and the three organs formed at 16 dph. Spleen formed at 18 dph. The growth curve of total height, pre-anus length, eye length and side length of lower jaw during 0-75 dph were also described in the present study.
