I think is not possible to directly help, as we don't know the data, but I tend to be fan of not transforming the data (other than scaling).
I paste a couple of references regarding variable transformation issues, focusing on ecological research:
as a simple example on how misleading can be even simple data transformations, and assuming you have in one plot half the biomass than in other...
finding the right transformation may be harder than it looks. From these examples, the only one that that can be easily 'back-transformed' is
sqrt(20)/sqrt(40) , that goes back to 0.5.
Better check what are the standards on your area of research (and what I know about fish biomass, like growth, it is normally modelled as non linear)