Scombridae: L III A11

Auxis rochei (Risso, 1810), Katsuwonus pelamis (Linnaeus. 1758), and Euthynnus affinis (Cantor, 1849)

Bullet tuna, Skipjack tuna and Eastern little 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 a few pale yellow dots on the embryo, and black on the oil globule (A & A1). The oil globule is clear to pale amber. The yolk surface is finely rough (goose-pimpled). B-stage eggs have more and larger yellow spots on the embryo, forming into clusters. Just prior to hatching, the yellow pigment has formed 4 clusters on the embryo, behind the eyes, mid-trunk, anus and mid-tail, plus a cluster on the oil globule (B1). Black pigment follows a continuous line around the head and down the body (B2). 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, and a high myomere count, which immediately identifies this species (C, D & E).  By day 4, all yellow pigment had disappeared (G). At 23 days a reared larva was postflexion (H2), with 5 preopercular spines, the longest equal to pupil diameter (H). 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: 3 days, G: 4 days, H, H1 & H2: 23 days (25-26°C).

The larva was not difficult to rear, but the egg was neglected after an early success to 23 days. However, twentyone larvae have now been barcoded, revealing a complex of species. Fifteen have matched 2 adult A rochii, 5 have matched 3 K. pelamis, and 1 has matched 3 E. affinis (all adults locally collected). Two other larvae, collected on 29 February 2008, and submitted as LIIIB10, matched E. affinis, giving a clue as to the appearance of an E. affinis egg, and making sense of a note in the collection record that February was too early for LIIIB10 (Pachymetapon grandis is a winter spawner). Further sequences are needed, with more care to see how the two species are being confused. I believe the egg shown in B1 might be Auxis rochei.

Linked samples	Offshore	Inshore
Eggs	4827	3555
Hits	74	63

This egg was common off Park Rynie, with as many as 900 being collected in a single sample. Eggs were only recorded in summer (blue graph), probably due to spawning adults ranging south into KZN waters at that time, as do dorado (FIIA4). It was the 12^th 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 (57%), 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.