| In present, for equations describing the growth of fish, one of them is derived by von Bertalanffy, i. e. equation (1);
w=winfinity[1-e-k(t-t0)]3 (1)
another is equation (2) derived by author (1994)
w=winfinity[1-e-k(t-t0)]r (2)
In this paper, four kinds of methods estimating, the parameters in equations (1), (2) are introduced. Meanwhile, it is pointed out that these methods have certain deficiencies: either the models used are not appropriate or the assumptions made are unrealistic. Thus, in this study a new method (search and approximation method) is put forward based on equation (2) and less assumptions. To do this; r is discreted and remainder error is taken as a scale. Then much better parameters are obtained by searching and approximating. On the basis of the measurered data of the Platycephalus indicus, the equation of the body weight growth is derived as follows:
w=1256.156[1-e-0.2297(t-0.28976)]1.44
Let (For the equations please see the PDF file.)
where w^ ij denotes the weight of the flathead at age i by using the kind j of methods, j=1, 2, 3, 4, 5. Thus, S1 = 88.13, S2 = 69.59, S3 = 78.71, S4 = 84.29, S5 = 65.46. Taking δj = (Sj - S5)/S5, δ1 = 35% , δ2 = 6% , δ3 = 20%, δ4 = 29%. Obviously, the search and approximation method is advantage to the other methods.
In addition, the process of the sample data corresponding this method is also discussed much better in this paper. |
