Spawning and Development of the New Zealand Sprat, Sprattus Antipodum (Hector)

III. Development of the larvae

III. Development of the larvae.

By 7.0 - 9.0mm body length (Fig. 12) the yolk sac has been completely absorbed and the mouth has assumed its functional shape. The dorsal fin is prominent by 8.0mm, and the intestine is tightly convoluted, with a row of superficial melanophores above its dorsal side. There is also a single melanophore just above the origin of the pectoral fin. The notochord turns dorsally and the hypurals develop at about 12mm. The anal fin also appears at this length, and the tail assumes a slightly heterocercal shape (Fig. 13). At 19.0mm pelvic fins arise alongside the pyloric region of the gut (Fig. 14), and the full complement of vertebrae (44-46) are evident in stained specimens. The tail is now homocercal.

During the colour change the body deepens markedly, becomes laterally compressed (Fig. 18), and the ventral edge of the belly becomes noticeably curved and armed with enlarged, pointed scales which give it a serrated appearance (Fig. 17). There is also considerable migration of fins and the anus along the long axis of the body during late post-larval life; the pelvic fins migrate backward over two myotomes (17th-18th), the dorsal fin migrates forward over seven myotomes (25th-18th), and the anus migrates forward over four myotomes (35th-31st).