Identification

In the absence of a complete collection and identification of all species of eggs and larvae which may be present in the plankton, it is not possible, of course, to state with certainty that no other species will present some or all of the same characteristics as those described above. Indeed, the early developmental stages are conspicuously devoid of any prominent characters which immediately place them in any one restricted category. The eggs, for instance, belong to a very large group of pelagic teleostean eggs which have a smooth spherical membrane, a small perivitelline space, a single oil globule, and a clear, almost featureless, yolk. They lack the characteristic elliptical shape of the anchovy (Engraulis), the cellular yolk and large perivitteline space of the pilchard (Sardinops), or the multiple oil globule of the yellow-eyed mullet (Agonostomus forsteri). The description of the larval stages could also apply with only minor modifications to a great number of genera.

Perhaps the most useful general characteristic, particularly in the case of the egg, is size. By this means the eggs of a great number of other species may be immediately eliminated from any sample. Table II gives the diameters of various spherical eggs which have been collected in the Hauraki Gulf during the snapper spawning season. With the exception of Sardinops all eggs have been taken from the female of the species named, and thus are positively identified. The pilchard eggs were taken from the plankton and identified by their close resemblance to other species of the genus in Australia and South Africa (Munro 1945, Davies 1954). All measurements have been taken from material fixed in 5 per cent, formalin. At least in the case of the snapper, shrinkage of the egg membrane is so slight that the live material is not likely to deviate appreciably from these figures.