About a fifth of the world’s annual wild fish catch, amounting to about 18m tonnes of wild fish a year, is used to make fishmeal and fish oil, of which about 70% goes to fish farms

https://www.theguardian.com/environment/2021/feb/11/global-salmon-farming-harming-marine-life-and-costing-billions-in-damage

Among other environment impacts too. All kinds of fish farms dumps lage amounts of waste into the environment

For a world annual shrimp production [in fish farms] of around 5 million tons, 5.5 million tons of organic matter, 360,000 tons of nitrogen, and 125,000 tons of phosphorous are annually discharged to the environment

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3353277/

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[–] usernamesAreTricky@lemmy.ml 3 points 5 months ago* (last edited 5 months ago) (2 children)

Going to almost certainly be less than 1. Moving further up the food chain results in energy losses. Those fish are going to use energy for their own body and such

Moreover there's high mortality rates inside of fish farms for fish themselves. From the linked earlier article

Fish mortality has more than quadrupled, from 3% in 2002 to about 13.5% in 2019, in Scottish salmon farms alone. About a fifth of these deaths are recorded as being due to sea lice infestations, but about two thirds are unaccounted for so the real mortality owing to sea lice – which feed on salmon skin and mucus, effectively eating the fish alive – could be much higher.

[–] kogasa@programming.dev 2 points 5 months ago (1 children)

Going to almost certainly be less than 1. Moving further up the food chain results in energy losses. Those fish are going to use energy for their own body and such

For sure, which is why I said "another food source would be needed." I had in mind something like the wild-caught fish being processed into something useful as part of a more efficient food chain, e.g. combined with efficiently-farmed plant material.

Moreover there’s high mortality rates inside of fish farms for fish themselves.

I don't have any context on the other pros and cons of fish farming, so definitely not arguing whether they're a net positive or not.

[–] usernamesAreTricky@lemmy.ml 1 points 5 months ago (1 children)

Don't really see how it'd make it any more efficient

In a new study out Monday in the journal Fish and Fisheries, researchers say that the vast majority of fishmeal is actually made up of fish deemed suitable for "direct human consumption." [...] Researchers say a whopping 90 percent of that catch is considered "food grade" and could be eaten directly

https://www.npr.org/sections/thesalt/2017/02/13/515057834/90-percent-of-fish-we-use-for-fishmeal-could-be-used-to-feed-humans-instead

Not to mention there's other effects of fish farms outside of just the overfishing part that I didn't even list earlier. They're actually a big player in mangrove deforestation, for instance

Conversion to aquaculture is the most prevalent driver of mangrove deforestation across the tropics over the last 50 years generating substantial carbon emissions. Preventing further aquaculture expansion within mangrove forest areas will be essential to achieve national emission reduction targets in mangrove-holding countries.

https://onlinelibrary.wiley.com/doi/10.1111/gcb.14774

Or antibiotic usage

High frequencies of antibiotic-resistant bacteria have been reported in sites near aquaculture where antibiotics have been used, demonstrating that modified antibiotics in an aquaculture facility have a high potential to exert selective pressure and increase the frequency of antibiotic resistance in other environmental bacteria [40,41]. In the aquatic environment, 90% of aquatic bacteria show resistance to at least one antibiotic, and approximately 20% were multi antibiotic-resistant. [...] An important and at the same time worrying aspect is that the antibiotics used in aquaculture include those used in human therapies, thus inducing resistance to these antibiotics

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8198758/

[–] kogasa@programming.dev 1 points 5 months ago

Being suitable for human consumption doesn't mean it's not also suitable for playing a role in a more efficient food chain

[–] AnUnusualRelic@lemmy.world 1 points 5 months ago

Have we tried farming sea lice? It's probably just like shrimp.