Synchrony of oocyte development with respect to vitellogenesis differs between fish with group-synchronous (left) and asynchronous (right) oocyte development.
Time is represented by discrete stanzas from the immature class (a, b), to the mature, pre-spawning class (c), to the spawning class (d, e). Prior to vitellogenesis, the pattern for each type of synchrony is the same among immature females (a,b): germ cells are initially composed of oogonia (a) and then primary oocytes emerge (b; oogonia + 1°, where the truncated dotted mode [right] represents a reservoir of both oogonia and previtellogenic oocytes that persists from year to year in iteroparous fishes). Once vitellogenesis occurs, it can occur in two patterns, each with different consequences. With group synchrony (left), annual fecundity equals the standing crop of vitellogenic (2°) oocytes once the 2° oocytes are readily distinguished (i.e., completely larger) from 1° oocytes but before spawning begins (c). Once spawning begins (d), the standing crop of 2° oocytes diminishes (e) as some cells become tertiary (= mature; 3°) oocytes, either in batches (shown here) or in one uninterrupted wave (i.e., total spawning, not shown). With asynchrony (right), annual fecundity cannot be determined at a single point in time because the standing crop of secondary oocytes is replenished during the spawning periods (i.e., de novo vitellogenesis). Oocyte size is scaled relative to a relative egg size of 1.0.