My father always fed meat meal to the hens, which would be much the same as fish meal. It was readily available through Dairy farm stores and was made from rendered animals. Unfortunately the emergence of CJD and variant, has made this meal carry much stricter rules for feeding and it is harder to find as a result.

Also chook meal that has been prepared, has an animal (sometimes a soy)protein added, so just like a lot of human convenience feed, many of us find we don't need to mix our own.

I do however buy fish scraps (pet food) from the local fish monger. It is what is left over from filleting. I cook this under pressure in the pressure cooker as it makes the bones go soft and brittle, and I feed this to my hens. They get about .5 kilos between 10 hens about every 10 days when they first start to lay again after the winter. I also use it in the autumn when they start to moult.
They go into a feeding frenzy when I arrive with the fish, and they devour everything, including the bones.