Growth Curves and Accuracy?

Hello,

I have been working on some formulas to approximate the biological needs/impact of a fish as it grows. It is obvious to me that a growing fish is going to have a greater impact on its environment than an adult fish of equal length. What is not obvious is just how much more of an impact it will have. To that end I have created a few differential equations that all account for the endpoints of a fish's growth, but I am not sure about the middle. Any thoughts would be appreciated. I have made an image so that you guys can see what each one looks like (see attachment).

Thanks,
MOA

 

I think the curve is something along the bottom line because the mass grows proportionately greater with increase in length. Something on the line of double growth in length x quadrupled growth in mass.