Дефиниција: Active swimming organisms that live in the water column and are able to move independently of the water mass (adapted from Lincoln et al., 1998).
Дефиниција: The mortality rate doubling time (MRDT) is considered to be a measure of the rate of ageing. It is estimated from the slope of the Gompertz curve by: MRDT = 0.693/G where G is the exponential (Gompertz) mortality rate coefficient.