Without turning this into a science fest, here's a brief overview from searching a few online database archives (they would be ones you have to pay to view, but my job comes with access passwords to keep on top of research papers)
You might ask...
What proteins, specifically in beefheart, are beneficial to fish, and what enzymes do fish have that allow them to utilise said proteins?
If the argument is simply that beefheart is high in protein, and therefore must be good for all animals that need protein, including fish, regardless of the type of protein that's either in beefheart, or the type that various animals use/need - that's not an argument. That's anecdotal assumptive reasoning with absolutely no logical or scientific base in fact. By that reasoning, I should be able to feed fish lionfish toxin as well.
Tropical fish nutrition was barely even a science back in 'the golden age of beefheart' and has advanced in huge strides since then.
When beefheart was first used/recommended, it was solely because of palatability, price, availability and resulting rapid growth - none of which reflect whether or not it's truly healthy for fish.
Understanding of proteins, fats/lipids in fish, and fish nutrition/metabolism was in its infancy (if even existent) when beefheart 'exploded' onto the Discus scene (as well as some of the fundamental differences between mammalian and fish protein structure/metabolism pathways)
Animal fats and oils are simply designed to be of the relative fluidity/solidity they are for a particular range of temperature, that of the mammals themselves. The oils in beefheart are liquid at the internal temperature of a cow, and will congeal to a semi solid in a fish, where internal temperature is lower.
(sourced from various Discus publications - Wattley, Axelrod
et al)
As I mention above, without turning this into a science fest, best I leave it there - if you'd like a list of further references to delve deeper, just PM me and I'll happily pass them on
TLDR: chuck the beefheart in the bin
Edited: spelling
