Acanthuridae: L III G4

Acanthurus triostegus (Linnaeus, 1758)

Convict surgeon           


Egg diameter in µm

Number of oil globules

Diameter of oil globule in µm

Yolk texture

Perivitelline space

Position of oil globule at hatch

Gut length   at eye- pigment stage








32% of NL



Egg: This egg usually has a few yellow pigment spots on the embryo (B), with fine black spots edged around the head of the embryo, and down the body in two fine lines, meeting at the tail, visible on a white background. The oil globule is clear to pale amber, and usually does not have pigment spots. Incubation is 24-26 hours. Spawning seems to be confined to evening.

Larva: The three white-yellow spots (eyes anus and mid-tail) usually separate this larva from all except LIIIF2 (C & C1), but by day 3 the serrated finfold edge confirms this species. The dorsal finfold serration begins above the anus (D, black arrow, with another arrow pointing to two neuromast bases in the dorsal finfold).  By day 4 all white pigment has been absorbed, except within the thorax (E).  B: NH, C: 1 day, D: 3 days, E: 4 days (26°C). Plate D1 shows the rough spiky serrated finfold edge clearly.

Plate E matches well, Randall’s (1961) figure 12. All attempts to rear this larva, failed.  Ten hatched larvae have been sequenced, 9 of which match the sequences of 5 adult A. triostegus, while 1 larva matches 4 adult Acanthurus nigrofuscus (BOLD). All adults collected locally.


Linked samples Offshore Inshore
Eggs 2916 1296
Hits 47 105

This is a summer spawner, both off Park Rynie (blue graph), and in the DHM (green graph). It was the 26th most common egg offshore, and 16th most common in the DHM samples (Introductory Notes, Tables 2 & 3). The egg appears to have become more abundant off Park Rynie recently, than in the first half of the study period (white graph). The Park Rynie linked samples showed more eggs offshore (69%), but the percentage is below the two indicator species, suggesting spawning around the 40m depth contour. This is surprising for an inshore species, but its abundance on the Aliwal Shoal will contribute to more eggs in offshore samples. See Section 7.3 and Table 1 of the Introductory Notes, for more information on the linked samples.