age0

Age0, often written as age-0 or age-0+, is a term used in demography, ecology, and fisheries science to denote individuals in their first year of life. The concept serves as a practical life-stage category that helps researchers organize data, build population models, and assess growth and survival during the earliest stage after birth or hatching. In fisheries, age-0 typically refers to fish hatched in the current year and not yet reached one year of age; in broader ecological contexts, it can denote the initial life stage from birth through the end of the juvenile year. The exact duration of the age-0 period varies among species and taxa.

Age-0 is a focal point for studies of recruitment, because survival during this stage strongly influences year-class strength and future population levels. Factors affecting age-0 survival include temperature, food availability, predation pressure, habitat quality, and hydrological conditions. Researchers may measure age-0 populations using capture surveys, netting, or visual counts, and they often determine exact ages by examining growth indicators such as otoliths (ear bones) or scales, which reveal annual rings.

Limitations include variability in growth rates and aging methods, which can complicate classification and comparisons across regions or years. Misclassification of ages can occur if growth is rapid or environmental conditions suppress typical aging markers. Despite these caveats, age-0 remains a widely used shorthand for the initial life stage in many organisms, particularly fish, and it plays a central role in population dynamics, stock assessment, and ecological monitoring.