Biology of Finfish and Shellfish

Acanthuridae

• Pre flexion larvae are of moderate depth until about 2.3 mm, after that they are deep in both head and trunk; they become even deeper following flexion; They are strongly compressed laterally, and the tail is much less deep than the trunk.
• They have 21-23 myomeres (5-10 + 11-16).
• The gut is coiled in smallest specimen and extends to 44-61% BL in pre flexion larvae.
• A small, often inconspicuous, gas bladder is located above the anterior portion of the gut.
• The snout is long, resulting in a triangular head.
• The mouth is small (never reaching the eye) and terminal with small conical teeth that form in both jaws at about 4rnm.
• The round eye is moderate to large until after about 15 mm, when it is consistently large. Head spination is extensive.
• Larvae (1.8 mm) have a serrate supraoccipital crest over the brain.
• The first fin elements to form are the elongate second spine of the dorsal fin and the pelvic spine; these are first visible at about 2.3 mm.
• The rays of the pectoral fins begin to form after flexion (4.6 mm). By 5-6 mm, full complements are attained in the pectoral, anal, and dorsal fins.
• By 8 mm, all pelvic fin elements are present.
• The elongate pelvic spines and second spines of the dorsal and anal fins reach maximum relative length between 12 and 17 mm; the first spines of the dorsal and anal fins remain markedly short.
• Acanthurid larvae are generally lightly pigmented but may have localized areas (for instance, the gut) of heavy pigment.
• Pre flexion larvae are moderately pigmented on the brain and gut; melanophores may also occur along the throat, on the lower jaw, and on the dorsal surface of the gas bladder.
• Following flexion, further pigment may appear on the head, along the lateral surface of the tail, on the bases of the dorsal and anal fins, and on the membranes of the caudal-fin rays and the first two dorsal-fin spines