Cows eat grass for protein, we can't really skip the middle man and eat grass to get protein.
I don't know if it's true, but it wouldn't be unusual for there to be benefit from getting omega 3 from fish rather than algea because of something like this. AFAIK, we mostly only know about the benefits of eating fish.
for example, you can tell exactly how much protein is in 100g of a complete protein like tofu when compared to 100g of something gross like beef.
similarly, my algae-based capsules contain 1210 mg of omega3s per serving, with 660mg of EPA and 440 of DHA.
> we mostly only know about the benefits of eating fish
nope, this study describes consumption of omega3s, not fish per se.