Fish poop acts as a carbon sink

Anchove poop
It doesn’t look like much, but fish poop acts as an important carbon sink in our oceans.

Fish move carbon from the surface of the ocean to the depths when they eat algae and poop it out, shows a new study.

In effect, fish poop helps mitigate the effects of climate change and are a crucial part of the “lungs” of our entire planet.

It’s fascinating stuff, we recommend you take a look at the full study.

We’re interested in how this finding relates to salmon aquaculture, which is much maligned for its impacts on the seafloor.

Fish poop can pile up under salmon farm sites. It can have a negative impact on habitat for stationary creatures (which are pretty much just worms at the depths we farm at in B.C.) But it has positive benefits, too.

The fish poop from our farmed salmon is mainly stuff that didn’t get digested, the carbon and stuff that’s left over after the nutrients the salmon need are used up. That stuff sinks to the depths (our sites are typically in water hundreds of metres deep) where it won’t have any opportunity to re-enter the atmosphere. It  also provides food for bottom-feeders (numerous farm sites in B.C. have experienced a boom in the prawn population nearby) which scrounge nutrients from the waste, and deposit their own carbon-rich leavings on the sea floor.

In effect, we are taking carbon from the surface of the ocean via the fish used to make fishmeal and oil, and from on land, via the plants grown to use in fish feed, and depositing the carbon deep in the ocean.

And as we find better ways to make salmon feed with less fishmeal and oil, by using alternative protein sources such as algae, it won’t be long and salmon farms will be helping reduce greenhouse gas emissions even more than they already are (by being one of the best forms of agriculture when it comes to low greenhouse gas emissions).

Farmed algae will inhale carbon dioxide and exhale oxygen. That algae will be fed to fish, and the carbon taken out of the atmosphere and trapped in the algae will be pooped out and sink to the depths of the ocean.

So rather than complain about salmon farm waste, critics should be finding ways to help make fish feed free of fishmeal and oil, and to make it commercially viable. Some farmers have already had success with such feed in trials, and it’s only a matter of time before fishmeal and oil are phased out completely, algae becoming the industry standard.

The critics who work with the industry on this will be able to talk about how they helped “green” up salmon farming. It’s an opportunity they should seriously consider, rather than promoting the false hope, and resource hog, of “closed containment.”



2 thoughts on “Fish poop acts as a carbon sink”

  1. What kind of algae do you see as being good for fish food? I’m not a biologist, but i suspect there are various varieties. We had some trout out of a lake in Custer State Park that were horrible. They tasted like algae. Not sure why, but hopefully this wouldn’t happen to a fish fed just algae. There’s a farm in Wisconsin growing algae for fuel production. Maybe their approach could be redirected to make fish food instead of fuel.

    1. Thanks for pointing this out Curt, you have hit on one of the biggest challenges in making fish feed. What animals eat influences how they taste. Salmon feed companies have been working for years to fine-tune their recipes to make sure the fish eating the feed will be healthy, but will also taste good and provide humans with optimal nutritional benefits.

      It’s tricky to substitute out the traditional primary feed ingredients, fish meal and fish oil, which provide Omega-3s (and a lot of flavour), with algae and still retain the flavour and nutrition benefits. But it’s happening. There’s a lot of interesting research being done on this, and several companies are already doing trials, experimenting with many different strains of microalgae to see which ones provide the best health benefits and best-tasting product.

      To directly answer your question about which strain, there are many different varieties, and many have been developed in research labs by selecting and breeding existing strains for their beneficial properties. Quite a few of them can be grown for fuel (taking just the fat from the algae) as well as for fish feed (using what’s left over after taking the fat). Kona in Hawaii is experimenting with this, growing algae for fish feed and for fuel. Perhaps the farm in Wisconson you mention could grow algae for both uses, as well.

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