"It is not possible to predict how much it will eat."
-I agree with this statement.
"But lets say I can know EXACTLY what each fish is going to eat each day because I give each fish a weighed ration in isolation of competitors."
-I'm not sure how you get to this statement from the previous sentence unless you are playing in the purely theoretical realm;
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.
