Ephippidae: L II A6A

Tripterodon orbis Playfair, 1866

Spadefish

 

Egg diameter in m

Number of oil globules

Diameter of oil globule in m

Yolk texture

Perivitelline space

Position of oil globule at hatch

Gut length at eye- pigment stage

Myomeres

1225-1345

1

240-310

clear

narrow

stern

38% of NL

24

 

Egg: When fresh, this egg has a multiple oil globule, all clustered together (A). Within 24 hours it has coalesced into 1. Such fresh eggs were rarely seen off Park Rynie, but a number were collected one early morning in February 1988 on a sea-cruise to Ledsman Shoal, north of St Lucia, and they hatched in 34 hours aboard ship (28C). The oil globule and early embryo are brown-amber on a white background. Big straw-yellow pigment spots cover the embryo, and totally hide the oil globule, assisting to separate the late stage egg from the previous species (LIIA6; Atractoscion aequidens), with which they were initially confused. The general lack of pigment spots on the yolk, and time of year, are other clues (if it's December, it's probably Tripterodon). Incubation is about 45 hours (24C).

Larva: The finer yellow finfold trim, and yellow pigment in 4 tail patches to the tip of the notochord (B & C), separate the larva from LIIA6. Yellow pigment in front of the eyes, and large pectorals, unusually interwoven with stringy yellow pigment (D1 & D2), distinguish the 5 day larva (D). At 9 & 14 days, a supraoccipital crest is well developed (E & F), and the larva is undergoing flexion. At 20 days the juvenile was postflexion (G). B: 1 day, C: 2 days, D: 5 days, E: 9 days, F: 14 days, G: 20 days, H: 38 days (26C). D2 is an unusual view of a 5-day larva, lying head-down, to show the pectoral fins.

This species proved quite easy to rear, and a voucher series is preserved. The DNA barcodes of 8 larvae are currently available, which match 4 adult T. orbis collected locally (BOLD).

 

Linked samples Offshore Inshore
Eggs 116 312
Hits 24 41

The spadefish is a summer spawner off Park Rynie (blue graph). The egg was not seen in the DHM samples. Annual catches off Park Rynie show no apparent trend (white graph). The Park Rynie linked samples had more eggs inshore (73%), suggesting most spawning occurs on or inside the 30m contour. Shoals of this species are seen on the Aliwal Shoal, and were targeted by spear-fishermen before the area was declared a MPA in 2005. The linked samples suggest they spawn closer inshore as well. See Section 7.3 and Table 1 of the Introductory Notes, for more information on the linked samples.