Question: ".won't the gape of an overweight fish be smaller than expected?"" You will see some variation in the mouth gape of individual fish species. The amount of variation is part of the data set for each species. The average or normal is what is most important to get general ideas about what that fish species can eat. IMO on average, overweight fish are not the average but the exception in most ponds. In reality based on how most ponds are managed, older bass are probably more often underweight than overweight.
When taking gape measurements you can include the fish's weight but it is not necessary. The total body length with mouth width is more important than weight IMO.
