I think we should reserve judgment as to the nutritional value of crayfish. Northern Crayfish have been shown to have an energy density comparable to RBT but to date I have not seen anything regarding nutritional value for LMB. Below is a listing I posted in an earlier post with reported energy densities.
Species................J/g Wet......Author
===========......======......================
Black crappie........4186..........Kitchell et al. 1974
Bluegill..................4186..........Kitchell et al. 1974
Common carp.......7524..........Cummins and Wuycheck 1971
Golden shiner.......4983..........Kelso 1972
Green sunfish.......4186..........Kitchell et al. 1974
Largemouth Bass..4186.........Rice et al. 1983
Northern crayfish...6153.........Stein and Murphy 1976
Northern pike.........3600.........Bevelheimer et al. 1985
Rainbow trout.........6069.........Rand et al. 1993
At first glance it may seem that northern crayfish are better than RBT but don't be quick to judge them to have more nutritional value than RBT
for LMB. Here is why. Crayfish are invertebrates and their exoskeleton comprises a not so negligible proportion of their weight and energy content. The exoskeleton is primarily composed of chitin. Chitin is a complex carbohydrate that is not easily digested. Only fish with the appropriate chitinase enzymes for digestion could extract energy from the chitin of crayfish. Part of that listed energy is probably not accessible to LMB. Are crayfish good forage? Yes, I think so. But we aren't going to understand crayfish digestible energy until we determine how well they support and grow LMB. This needs to be done in a laboratory setting to be reliable and to date I am not aware of any such tests.
Crayfish offer some benefits. They are a seasonal crop that is perishable and so when in abundant supply they are very cheap to buy relative to other forages. In the spring after winter consumption reduces forage numbers and before new crops of YOY replace them there is a window where Crayfish could provide a much needed supplement either to maintain or to grow large LMB. Regardless of the actual digestible energy, Crayfish are probably easier to consume than fish. So the time rate at which crayfish can be consumed is probably higher than fish giving LMB a leg up on total daily energy consumption. They have a place. It seems like Lusk once said that LMB will finish off crayfish supplements before resuming consumption of BG. This truly makes a lot of sense to me.
As Dave mentioned, everyone should have BG as core food produced in situ. Where the production is less than needed to achieve goals, any highly available forage at affordable prices can fill gaps that are occurring. It would seem to be important to understand when forage gaps will be occurring. Everyday is day that an LMB's metabolism is running and it will burn energy no matter what. They will eat everyday to maintain that energy burning and if they get any extra ... they will gain.
