Ambassidae: K III B9

Ambassis dussumieri (=gymnocephalus)

Bald glassy

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
620-680	1	170-190	clear	narrow	bow	33% of NL	24

Egg: These eggs are characterised by heavy yellow pigment on the embryo and oil globule, but not on the yolk except close to the oil globule (A). The oil globule is pale amber, but in the later egg, is masked by pigment. Three or four distinctive dark blotches, two behind the eyes, one mid-trunk, and one associated with the yellow pigment in mid-tail, are visible on a white background (A1). Incubation is about 24 hours. 

Larva: The heavy yellow pigment of the early larva, along with oil globule position and clear yolk, are useful in the identification of this larva (B, C & D). By day 4 all yellow pigment is lost except in the gut (E). At 13 days the larva had already reached postflexion (F). A & A1: eggs DHM, A2: eggs from St Lucia, September 1993, B: NH, C: 1 day, D: 2 days, E: 4 days, F: 13 days, F1 wild collected from Lovu estuary mouth, circa 14 days, G: 37 days (23-24°C).

A wild collected larva of approximately the same stage as Plate F, is included for pigment comparison (F1).

This larva was quite easily reared, despite the small egg, and the 37 day juvenile positively identified.  No DNA barcoding results are currently available for this larva. It remains to be seen, whether the egg off Park Rynie is the same species, via DNA barcoding.

An Ambassis egg was recorded from St Lucia estuary during the closed mouth period of September 1993 (Connell, 1996), when salinity at the mouth was 38 ‰. The eggs were not successfully reared to confirm which species was involved. However, careful comparison of A1 and the photograph of the St Lucia eggs (A2 above), shows the same distinctive dark patches in the eye sockets, midbody and midtail, of the embryo, which were not seen in the Ambassis ambassis eggs taken from the Msimbazi estuary (KIIIB9C). Thus I believe the egg taken in St Lucia in 1993 was A. dussumieri, supported by the high salinity at the time (see comments below).

This was the 11^th most common egg in the DHM samples (Table 2: Introductory Notes). The species is a summer spawner (green graph). The egg was much less common in the Park Rynie samples, with a similar scatter over the year (blue graph). In the Park Rynie linked samples, only 10 eggs were seen, all in inshore samples. The water at the DHM sampling site is coastal seawater, and, of the three Ambassis species found in KZN estuaries, A. dussumieri is regarded as the species which prefers more saline waters (S Weerts, CSIR Durban pers. comm.).This egg has not been seen off Park Rynie since September 2001.