The number of fatheads per pound is directly dependant on how big the FHM are. Obviously if they were fry there would be a lot more per lb than if they were old broodstock. I recall that this information has been provided in a past post. Instead of looking it up, here is close to what I provided earlier.
At abt 1" = 700-800/lb (plump vs thin bodied)
at abt 1.5" = 500-600/lb
at 1.75" =350-450/lb
at 2" = 290-325/lb
at 2.5" = 150/lb.

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