It took 100 million years for evolution to design cows and 400 million years of evolution have been impacting fish, so it will take approximately 4x as much investment or time to develop a "Further Than Fish" replacement
The replacement just has to taste very similar, not hurt animals, be reasonably priced, sustainable to produce and healthy or neutral for health.
Arguably cows have been impacted by as much evolution as any organism. It's not as though cows spontaneously generated 100M years ago - there were hundreds of millions of years leading up to cows becoming what we recognize today.