The issue is not the absolute number but that you are using more to produce less. Off course as someone else mentionned not all those fish might be ready for consumption.
But at the same time Norway toot Salmon farming as efficient but are all externalities really taken into account ?
> The issue is not the absolute number but that you are using more to produce less.
But this will always be the case when growing animals. The 83% number seems quite efficient to me.
I'd bet that the weight of a cow is a way smaller percentage of the weight of grass needed to grow it. Surely closer to 1%.
Yes. The question is: should we continue growing animals then?
We cannot directly eat grass or grass products, grassy lands depend on big ruminants to thrive, and are often unsuitable for intense agriculture.
Grass is one of the most efficient ways of nature to turn sunlight and water into biomass. Feeding animals on it and using animals products for humans is a great way to use resources.
Of course, that doesn't necessarily imply eating their meat. In India, cows are holy and only their milk and milk products are used to feed people.
But it's quite certain it will stay more efficient than a cow (But efficiency is not everything since I can't eat grass; and yes I'm aware that quite a number of cow has never seen a blade of grass).
I was under the impression that's how it is with all animals, they always need to eat more than what you get from them in terms of calories which usually will also equate to more weight (the comparison used here) in than out.
Otherwise we'd have found some feeding process that's over 100% efficient which doesn't seem possible.
In other words, they poop while they grow, unlike plants where the efficiency looks better.
You are feeding fish to fish to produce fish. Of course this is not the exception as someone else mentioned:
> 95% of soybeans grown in South America are used to feed livestock in Europe, even though soy is already a complete protein and could be used
Sources (sorry, in Spanish... it's rather difficult to find info about fish in English if you're Spanish, because we don't eat the same species, we don't even name the same species, and when we do, there is not necessarily an one-to-one map between Spanish and English names).
https://www.elconfidencial.com/tecnologia/ciencia/2019-10-17... https://www.elmundo.es/elmundo/2012/04/24/natura/1335258947....
Personally I strongly prefer the taste of some of these species they feed farmed fish than that of the farmed fish themselves.