A

abbreviation for acre (4046.9 m², 0.405 ha, 43,560 ft², 4840 yd², 0.00156 mi²)

abbreviation for anal fin (rays)

annual total mortality rate (the number of fish which die during a year divided by the initial number. Also called actual mortality rate, coefficient of mortality (Ricker, 1975))

abbreviation for annum, meaning year. Usually used in combination, e.g. Ma, meaning million years