I used a trout filet that weighed in at 0.384kg (a bit under a pound) and I added 100mg of B1 and 2tsp. of RepCal.
I don't know how much fish Alan started with, as I've not seen the original recipe, but it makes sense that you'd have to adjust according to the quantity.
*my jar of RepCal gives specific amounts to use per pound of food*