Scombridae: L III A11
Auxis rochei (Risso, 1810).
Bullet tuna.
|
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 |
Myomeres |
|
865-960 |
1 |
220-265 |
clear |
narrow |
stern |
37% of NL |
41 |
Egg: This egg turns up like clockwork in the summer, and can be seen in two different stages (A, B & B1) suggesting spawning in the evening and morning. A-stage eggs have fine black and evenly scattered pale greenish-white dots on the embryo, and black on the oil globule (A & A1). The pale spots to not extend far past the anus (A1). The oil globule is clear to pale amber. The yolk surface is finely rough (goose-pimpled), but the yolk is not segmented. B-stage eggs have slightly larger greenish-white spots on the embryo, but still evenly distributed. Black pigment follows a continuous line around the head and down the body (B1). Incubation is about 30 hours. A curious feature of this egg is that the majority sink to the bottom of the bowl during sorting, if development is advanced.
Larva: The early larva has a characteristic pattern of yellow (C, D & E), and a high myomere count, which immediately identifies this species from all but the other two summer spawning scombrids E. affinis (LIIIA11A) and Katsuwonus (LIIIA11B). By day 4, all yellow pigment had disappeared (F). At 23 days a reared larva was postflexion (G2), with 5 preopercular spines, the longest equal to pupil diameter (G). At this stage it had developed a small crest above the eye (arrowed in H but more clearly seen in H1). The crest is further forward than the supraoccipital crest of Sarda and Scomberomorus (Richards, 2006). C: NH, D: 1 day, E: 2 days, F: 4 days, G, G1 & G2: 23 days (25-26°C).
The larva was not difficult to rear, but the species was neglected after an early success to 23 days. Twenty eggs have been barcoded, matching 2 locally collected adults (BOLD).
 |
 |
| Linked samples | Offshore | Inshore |
| Eggs | 11332 | 7573 |
| Hits | 160 | 119 |
This egg was common off Park Rynie, with as many as 4000 being collected in a single sample. Eggs were only recorded in summer (blue graph), although the species is seen all year round on the KZN coast. It was the 10th most common egg off Park Rynie (Table 3: Introductory Notes). It was seen twice in the DHM samples, in January and February. Abundance in samples through the years of the study has remained fairly constant (white graph). The Park Rynie linked samples showed slightly more of these eggs offshore (60%), but the low percentage suggests spawning is primarily inside the 30m contour. See Section 7.3 and Table 1 of the Introductory Notes, for more information on the linked samples.