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Annual fishes can maintain permanent populations in temporary aquatic habitats since the population survives dry seasons in the form of diapausing eggs. Populations persist even though subject to erratic environmental cycles and recurrent ecological catastrophes.Developmental arrest occurs at one or all of the following stages: Diapause I (Dispersed cell phase); Diapause I1 (Long somite embryo); Diapause I11 (Prehatching). In Austrofundulus, Diapause Survival strategy is based on the "multiplier effect"; i.e., interposition into the developmental pathway of three branch points containing diapause stages of prolonged, variable duration generates eight different distributions of total developmental time. Thus, a single egg population of identical age can generate several subpopulations, all of which develop according to different schedules. A developmental program is established which permits the repeated loss of individual eggs under conditions which may initiate hatching but do not allow for maturation and successful reproduction. The "multiplier effect" augmented by other adaptations guarantees that some portion of the egg population will survive to reproduce.

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Comparative studies of annual fish development reveal a unique developmental pattern in which embryogenesis occurs within a reaggregated mass of previously dispersed cells. The normal development of Austrofundulus myersi Dahl, a representative annual fish, has been divided into 46 stages. Cleavage during Stages 1–11 produces a typical teleost blastula. At Stage 12 (a flat, hollow blastula), the blastomeres segregate into two populations. One population composed of deep blastomeres will disperse as amoeboid cells, while the other, an hemispherical shell of outer blastomeres, flattens to form the enveloping cell layer. The cells of the enveloping cell layer become multinucleate and the layer functions as an extra‐embryonic membrane which is shed at hatching. When epiboly commences (Stage 14), the deep blastomeres come together as a consolidated mass and then migrate outward as individual amoeboid cells into the space formed between the expanding enveloping cell layer and periblast. When epiboly is concluded (Stage 19), the deep blastomeres have completely dispersed over the surface of the periblast. The dispersed phase usually lasts for several days. Prior to epiboly and during the dispersed phase, no germ ring, embryonic shield, or axial organization is present. The dispersed cells come together to form a definitive aggregate (Stage 22) by day 4. Embryogenesis within the reaggregated mass of previously, dispersed cells produces a typical teleost embryo. The definitive embryonic axis and solid neural keel appear by Stage 28 (day 10). Growth and organogenesis proceeds and hatching occurs at Stage 44. Development through Stage 44 requires 39–40 days in non‐diapausing eggs. Eggs of A. myersi may enter diapause at three distinct stages: (1) dispersed cell phase; (2) long somite embryo; and (3) late pre‐hatching.

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