Fish Population Dynamic and Stock Assessment

3.1.3.5. Growth rate

The growth rate is denoted by

$${\triangle L \over \triangle t}={L (t+\triangle t) - L(t) \over \triangle t}$$ ………………… (1)

Time (or age), t is usually expressed in units of years.

The mathematical relationship between the length of a fish and the growth rate at a given time is a linear function.

$${\triangle L \over \triangle t}= a + b ^\ast L(t)$$ …………………(2)

Using VBGF equation, linear relationship can be derived as follows :

$${\triangle L \over \triangle t}= K ^\ast (L_\infty - L(t)) \ cm/year$$ ………………… (3)

where K = - b and $$L_{\infty} = -a/b$$

The mean growth rate (in length) can be calculated using the equation

$${ \overline L_t}={L(t+ \triangle t) + L(t) \over 2 }$$ …………………………… (4)