Lethrinidae: K III B3A

Gymnocranius cf griseus (Schlegel, 1844)

Grey barenose

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
625-720	1	145-190	clear	narrow	midway-bow	35% of NL	24

Egg: This egg has no outstanding features, and needs to be hatched to gain further clues to its identity. The oil globule is light pink to amber. The developing embryo has some pale yellow pigment which is difficult to see. The midway positioning of the oil globule, and summer spawning period are other clues. These eggs often hatch during the sample separation process, indicating that incubation is 24-28 hours in summer, assuming evening spawning. 

Larva: The early larva can be confused with the pale form of Secutor (LIIIF5), which can be avoided only by rearing to the 2-4 day stage, when the lack of yellow pigment, and lack of a line of “pimples” in the finfolds ( see LIIIF5), assist in separating the two. B: NH, C: 1 day, D: 2 days, E: 4 days (25°C).

This egg (and subsequent larva) is also similar to EIIIB8, but does not have a segmented yolk, and lacks the black spot on the snout of the Gerres early larva. The similarity to Secutor has probably resulted in undercounting of this egg, as it is not seen often, and spawns at the same time of the year. Twentyfour larvae have been barcoded, and match 6 adult Gymnocranius griseus collected locally (BOLD). Another 4 larvae, match the barcode of my adult Lethrinus rubrioperculatus, and another 4 larval sequences match my adult Parapercis maculata. Clearly this rather featureless egg is causing some confusion.

While Smith (1986a), lists both G. griseus and G. grandoculus (as robinsoni) occurring on the east coast of South Africa, more recent publications (Carpenter, 2001; Heemstra and Heemstra, 2004) state that G . griseus does not occur on the east coast of Africa. Barcoding of adult material from the KZN coast and Mozambique, has however revealed four species (my adult material, and specimens submitted to BOLD by SAIAB*; M Mwale pers. comm.). Whether the KZN G. griseus is identical to G. griseus from northern Australia, Malaysia, and Japan, requires investigation.

Linked samples	Offshore	Inshore
Eggs	234	156
Hits	26	32

The limited data suggests this species is a summer spawner (blue graph). The Park Rynie linked samples show 60% of these eggs in the offshore samples, suggesting they are spawning around the 30-40m contours. See Section 7.3 and Table 1 of the Introductory Notes, for more information on the linked samples.

SAIAB = South African Institute for Aquatic Biodiversity, Grahamstown.