Embryology, ethology and ecology of ontogenetic critical periods in fish.

Overviews of critical period concepts, as they appear at several biological levels, are presented. In embryology, critical periods generally refer to restricted periods in development during which undifferentiated groups of cells can be induced to differentiate. In neurobiology, critical periods are those during which neural circuits are particularly plastic and subject to molding by cellular processes and by experience. The ethological critical period concept advances the idea that an individual's behavioral characteristics can be more strongly influenced by a given event (some stimulus) at one stage of development than at others. For example, this is the period during which young birds imprint upon their parent(s) and learn their species' songs, or during which young salmon imprint to the odor of their home streams. The fisheries science critical period, an ecological concept, refers to a restricted time in the early life history of fish during which there is massive mortality. For many fish, this event is generally considered the primary factor controlling the size of the adult population. The cause of variable mortality between years is thought to be a result of differential food availability and predation during a critical stage in early fish larval development. At each biological level of the critical period, spatial and temporal overlap between the developing organism and specific environmental input is essential. It is likely that critical periods in embryology, neurobiology and ethology are causally interrelated in a hierarchical manner and that they can be manifested as ecological critical periods.(ABSTRACT TRUNCATED AT 250 WORDS)