Dear Mohammad!

C and WP are the seasonal parameteres of this growth function. 

C is the amplitude of seasonal growth oscillation and WP  is the Winter point

In the attached pdf you can find a description of these parameters and the calculation method of them.

Best wishes: Zoli

@Zoltan Podor

Thank you very much Zoli

Can we Estimate them in FISAT?

Dear Mohammad!

There is a package in R: fishmethods, I think you can use it, but i don't know it exactly

Zoli

I know its popular to do so, but 'm not sure that it is mathematically correct to use the Von Bertalanffy growth curve (which assumes continuous growth) to the discrete biphasic growth shown by Crustacea. You might be better to use a moult process model such as that described By Brylawski  et al. Canadian Journal of Fisheries and Aquatic Sciences, 2006, 63(6): 1298-1308. Apart from anything else, the VB curve assumes growth slows with age, but crustacean growth increment is a function of size at moult. It is the length of the intermoult period that determines if growth "slows". The resulting growth curve is not a classic VB curve.

See also Foo & Wang 2013 Stochastic growth models for analyzing crustacean data http://www.mssanz.org.au/modsim2013/B2/foo.pdf

C is the intensity of the (sinusoid) growth oscillations and determines the intensity of the seasonal growth. When C=0, seasonal growth is absent and the equation equals the standard VBGF. At C=1, growth comes to a standstill once a year at the winter point. Intermediate values of C indicate growth reduction during the winter, but growth never completely stops. In FiSAT both WP and C as entry (seed) value with step size. 

 WP is the Winter point or period with the slowest growth.

Yes, you can estimate in FiSAT. If your data is from tropical regions, this may be avoided.