2.2. Stock model
Shrimp biomass (bt) at time t was calculated using a stock model:
equation(1)
bt=wtnt
Turn MathJax off
where wt is mean individual weight of shrimp and nt is the surviving shrimp population.
A modification of the Hernandez-Llamas and Ratkowsky (2004) model was used to describe growth of shrimp:
equation(2)
wt=w0+(wf−w0)[(1−kt)(1−kc)]3,
Turn MathJax off
where w0 is the weight at the beginning of cultivation, wf is the weight at the conclusion of the cultivation period, k is a parameter representing the rate at which wt changes from w0 to wf , and c is the duration or conclusion of the period of cultivation (weeks).
Survival was modeled using the exponential equation:
equation(3)
nt=n0e−z.t
Turn MathJax off
where n0 is the initial population, and z is the instantaneous mortality rate. Nonlinear regression estimation was used to fit the growth and survival curves to data corresponding to each pond.