No not so. If an experiment is performed on fish in isolation where only that fish can eat its ration the conversion properties can be determined. Experiments just like this have been performed many times over. To be sure, I know it won't help you in any way. But yes, if consumption is controlled then conversion can be determined. AND the variation for a group of fish is small and the functions resulting from the analysis practical and effective.
The problem with this is : these fish are not in isolation, they are free to roam a pond, you have no idea how each fish metabolizes its food or how much energy each fish expels on a given day. I have fish that sit under my dock all day, they are on the larger side, I also have fish that roam around and explore, they really like swimming with the GC, why ? I don’t know but these fish are much more average size.
All I was trying to do is explain why I wouldn't use functions of gain (that depend on consumption and maintenance) to model length.
I am not sure what you are getting at. You think LMB that you see swimming with GC have higher metabolism than the LMB you see under your dock? You think LMB swimming with GC consume more than LMB under your dock but way less because of it? You think LMB which are of same age but weigh more are more efficient at conversion? It's really not clear and I am neither going to argue for or against whatever you may be thinking.
In the end, the reason I accept the laboratory results is because I have asked all those questions long ago. Most tend to agree that it takes 5 lbs BG to support 1 lbs of LMB for a year IN A POND. The laboratory results are consistent with that. So why should I argue against the laboratory with arguments like you mentioned above? If it takes 5 lbs according to the laboratory tests across a full climactic year, then maybe it makes no difference where the fish are. I am satisfied that for a population of fish I can apply the laboratory relationships to model average growth as a function of consumption.
It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers
