Physiology of early fish development: respiration and metabolism.

Several decades of intensive study on adult fishes have provided a relatively broad knowledge of gas exchange, iono- and osmoregulation, nitrogen excretion, as well as endocrine function. Much less is known, however, about these processes during early fish development. In oviparous fishes, the interaction between the developing embryo and the external environment is predicated by the physical structure of the encased embryo. The developing embryo proper and attached yolk sac are surrounded by the perivitelline fluid enclosed in a soft shell or chorion. After hatch, the gills are initially undeveloped and the cutaneous surface may play be an important exchange site. The major fuel is yolk protein and consequently, the nitrogen end-product ammonia may be a potential toxin to the developing embryo. In viviparous fishes, the maternal-fetal relationship must be considered, as well as the interaction with the environment. Another level of complexity when considering the physiology of early stages is changing nature of the growing and developing embryo and larvae. Papers on these and related topics are requested