Optimum Harvest Time of the Nile Tilapia ( Oreochromis niloticus ) in Honduras: A Two Step OLS Procedure to Obtain the Growth Function

摘要

Several aquaculture firms in Honduras lack a profit function for tilapia production, which complicates their decision-making. Furthermore, several statistical procedures used to obtain a production function are too complex for these firms to implement on their own. Thus, a simple, yet efficient, model was developed for these firms to follow. The model for this function consists of a gross-margin function composed of an income and a cost function. The OLS procedure in this model differs from several studies by using the OLS obtained length-weight parameter, “b” as an input to estimate “k” in a second OLS regression. The latter regression is applied to a log-lin model of a weight-based von Bertalanffy growth function. The estimated length-weight exponent, “b” used in the growth function, the growth parameter per day, “k” and the mortality parameter per day, “z” are 2.92289, 0.00821 and 0.00086 respectively. The optimum harvest time estimated for one period is 199 Days after Stocking (DAS) when there is no restriction in the market for the size of fish and 208 DAS when minimum market length is 20 cm. The optimum harvest time for infinite time horizon is 117 DAS if there is no size restriction.