Discussion

The eggs of Sprattus antipodum can be distinguished from all other non-clupeoid eggs in New Zealand waters by a combination of their size, segmented yolk, small perivitelline space, and absence of an oil globule. Although the eggs of the other two New Zealand clupeoids have segmented yolks, they are very distinctive and cannot be confused with those of the sprat: anchovy eggs are elongate-oval and measure 1.06 - 1.20mm by 0.48 -0.56mm (Marlborough Sounds collection) ; they have no oil globule. Pilchard eggs are spherical with a diameter range of 1.32 - 1.70mm (Baker, 1972). They have a wide (0.65 - 0.85mm) perivitelline space and the yolk contains a single oil globule.

The sprat and anchovy yolk-sac larvae are almost impossible to separate: their yolks lack oil globules and their body form is practically identical. The sprat larva appears to be slightly longer, and to have more pigment, than the anchovy larva at hatching, but I have insufficient material of the anchovy to support these apparent differences. Identification of the post-larvae of New Zealand clupeoid fishes has been dealt with in an earlier publication (Baker, 1972).

The eggs and larvae of the New Zealand sprat closely resemble those of the North Sea sprat, Sprattus sprattus L., in both morphology and development (see Fage, 1920 and Lebour, 1921).

The discovery of a long breeding season for S. antipodum confirms a suggestion to this effect by Morgans (1966), who made a detailed statistical study of the size distribution in a shoal of over 2,000 sprats stranded near Kaikoura. His results showed non-normal length distribution within year-classes, indicating that the sample consisted of mixed broods of sprats which were the result of a prolonged breeding season.