February 23, 2010 update: I discovered that the credit for the grasshopper photo was incorrect. The photo is actually from tazintosh's Flickr collection and the photo's Flickr page is here. My apologies to the photographer, who has a great collection of photos in his Flickr collection, including many other shots of plants and animals.
This is part 2 of a series on aquaculture, inspired by a recent article published by an international team of researchers in the Proceedings of the National Academy of Sciences. (See PNAS 106 (36), 15103–15110, doi: 10.1073/pnas.0905235106. Summaries available from Stanford University and Environmental Research Web.) My first Ethicurean post, "New research on aquaculture industry reveals murky waters surrounding fish-feed issue," looked at the current state of the industry: aquaculture supplies almost 50 percent of the world's seafood, but to do so it uses almost one-third of the wild fish captured at sea. This one will explore the pros and cons of the alternative feeds.
With almost all of the ocean's either fully exploited or overexploited, the future of our oceans and the aquaculture industry both depend on finding alternatives to wild fish. There are many alternatives currently available and many possibilities on the horizon, but they require us to ask a lot of difficult questions. Some of these are posed by the authors of "Feeding aquaculture in an era of finite resources":
...is the use of rendered animal products (e.g., feather meal, bone meal, blood meal) preferable to fishmeal as a protein source for farmed fish? Are genetically modified vegetable oils that provide LC omega-3 oils an acceptable substitute for fish oil? How should forage fish resources be allocated among competing uses: to the highest economic value (e.g., ranched bluefin tuna), to feeding the largest number of people, or to conserving natural ecosystems? What criteria should be used to assess the ecological effects of using forage fish for feeds?
These are tough calls, ones that will surely make waves in a variety of interest groups.
For an alternative feed to be a viable replacement for fish oil or fish meal, it needs to pass many tests. The feed must be nutritionally suitable, readily available, and easy to handle and ship. Some fish, like salmon, have additional needs, like high levels of omega-3 fatty acids, and so the overall feed package will need to result in fish with at least a minimum level of omega-3 fatty acids.
The authors of the article explored several alternatives to fish meal and fish oil: protein from plants grown on land, oils from plants, proteins and oil derives from single-celled organisms, rendered animal products, seafood by-products, and krill.
But before we examine these alternatives, an important note about how fish diets evolve as the fish grows. In many species, the youngest fish (often known as "starters" and "fry") require diets that contain a significant amount of fishmeal to help them grow. But as the fish reach their juvenile and "grow-out" stages (i.e., the period when the fish is being matured for harvest), they require less fishmeal, and so alternatives like the ones described below become more viable. It turns out that most farmed fish eat 95 percent of their lifetime food during these latter period, which means that finding alternatives appropriate for both the juvenile and "grow-out" fish will have a significant overall impact the fish meal and oil usage.
The feed alternatives
Proteins from plants: For these to be an option, they need to have low fiber and starch content. As the level of indigestible matter increases, so does the quantity of fish feces, and thus the environmental impact. It turns out that Tom Philpott's favorite item — distillers' grain (left) a waste byproduct of the ethanol process — has been used as feed for omnivorous fish. In cattle, its use seems to increase the amount of the deadly E. coli strain H7:O157, according to this KSU paper, among others. And in fish, too, distillers' grain has a significant downside: its high fiber content leads to more fish waste, and therefore more water pollution. In addition, the material is not palatable to fish, leading to a low feed efficiency.
Some in industry are thinking that the high waste rate from fish that are fed distillers' grain isn't a shortcoming of the feed, but indicates a problem with the fish. Basically, "if you can't get fish to eat what you're giving them, perhaps you need a new fish." And so, some are planning on selectively breeding fish to be more tolerant of plant-based feeds and other fish alternatives. If the breeding is done responsibly and doesn't create a new zebra mussel or other invasive pest, this seems like a potentially good approach. Fish have not been domesticated to the same extent as terrestrial livestock, so for most species breeding is a relatively young field. Breeding can create unwanted consequences, as we have seen in recent decades for many animals, like hogs that have been bred to be lean even on a grain diet, but have flavorless meat.
Oils from plants: Plants such as canola and soybean can be rich sources of oil that can be a limited substitute for fish oil. Current oils, however, have far lower omega-3 content, which makes them unsuitable for a complete replacement. The potential for this path is great: Atlantic (farmed) salmon can have 75% of fish oil replaced with good results, as long as omega-3 requirements are met by strategic doses of feed that contains fish oil (see this piece at Science Daily for more background).
A likely path to plant oils that contain high levels of omega-3 fatty acids is sure to cause a ruckus: creating them in the laboratory through transgenetic cross-breeding. The article suggests that we'll see such plants "within a decade," a promise I think we've heard before for a variety transgenic ventures (e.g. drought tolerance). With demand from the public for omega-3 supplements, there might be an additional financial incentive for plant developers to create crops that can also be fed to fish. A new transgenic soybean developed by Monsanto as a nutritional supplement and foods additive could be a possibility, as Science Daily reports.
The transgenic alternative made me wonder how long it will be before we see advertisements from biotechnology companies proclaiming that their genetically modified organisms (GMOs) are saving the oceans by offering a drop-in replacement for wild fish — if those ads don't already exist. For some, the fact that the transgenetic products are only in the feed — a situation analogous to the use of GM soy and corn in animal feeds, which even GMO-cautious Europe allows — makes their use palatable to many. Others won't be so easily swayed. (See previous Ethicurean posts on GMO crops from a farmer, agroecologist, nonfiction author, and genetic engineering expert.)
Single-cell protein and oil: Various single-celled organisms such as microalgae can be raised as a source of protein or oil. Some of the oils are high in omega-3 fatty acids — and are currently fed to chickens to encourage eggs with above-average omega-3 content — which makes them an excellent replacement for fish oil (Thraustochytrids have been used in the grow-out phase for Atlantic salmon). The cost for these oils and proteins is higher than fish oil, but the authors of the PNAS article expect that research aimed at producing biofuels from microalgae could lead to large cost reductions.
Rendered terrestrial animal products: The rendered leftovers from meat production — meat and bone meal, feather meal, blood meal, poultry byproduct meal, and more — are an economically attractive food source for aquaculture. The PNAS article states that poultry by-product costs $0.79 per kilogram of protein: by comparison, anchovies command $1.13 per kilogram of protein. Outside of price, they have advantages such as a better amino acid profile than vegetable proteins, but also disadvantages, such as higher rates of indigestibility because of high saturated fat content.
For those worried about the potential for "mad fish disease" (i.e., prions) from these feeds, the PNAS article claims that the rendering process destroys prions and that prions don't cross the intestinal barrier in the sea creature. Several scientists, writing in the Journal of Alzheimer's Disease, disagree, stating that "We are concerned that consumption of farmed fish may provide a means of transmission of infectious prions from cows with bovine spongiform encephalopathy to humans, causing variant Creutzfeldt Jakob disease."
If the aquaculture industry increases the level of transparency as they should, the inclusion of rendered wastes could lead to public outcry, as people are no more likely to want to buy farmed salmon that was fed rendered chicken dropping and waste than they are meat from cows that are fed this waste product today. (See Consumer Union reports for more about this horrid practice.)
Seafood byproducts: Fishing vessels and fish processing facilities generate a significant amount of material that could be used by aquaculture. But a sufficient quantity of byproduct is needed to justify the expense of a feed plant, so the opportunities for this alternative are limited to areas with high concentrations of fish processing, like the salmon plants in Alaska.
Krill: Krill, small shrimp-like invertebrates, are abundant in the world's oceans and could provide nutritious feed for farmed fish. However, they are one of the foundations of the aquatic food chain, and the authors caution that krill's role in aquatic ecosystems needs to be better understood before large-scale harvesting is undertaken. An article in the San Francisco Chronicle shows some of the ecological complexities off the coast of Northern California.
Insects: I was somewhat surprised that insects did not make the list of alternative. Insects can be easy to raise, will eat a wide variety of food, and can be highly nutritious. Over at Mental Masala, I wondered if swarms of locusts and other insects could serve as feed for livestock, noting that the Food Insects Newsletter had reported that the Philippine government encouraged people to harvest locusts as food for humans, cattle, and fish. I searched in the scientific literature for a few minutes and found a number of articles about the use of insects as fish food, including one in the Journal of the World Aquaculture Society that studies the use of black soldier fly prepupae (Hermetia illucens) or housefly pupae (Musca domestica) as a feed supplement for rainbow trout (Oncorhynchus mykiss); initial results were promising.
Since certain species of fly larvae eat manure, this creates the efficient and potentially unappetizing possibility of raising fly larvae on livestock manure, harvesting the larvae, then processing them for incorporation into fish feed, which would then help grow fish for human consumption, while the trimmings from the farmed fish could be turned into fish feed, livestock feed or another useful material. Some forward-thinking sustainable aquaculture operations already do this: as La Vida Locavore reports, Will Allen's amazing urban farm Growing Power feeds its farmed fish larvae from soldier flies that grow in its compost, for example.
The voyage ahead
Aquaculture feed alternatives are uncharted waters, with many hazards and uncertainties on the horizon: high costs, volatile markets for fish oil and fish meal, emerging feeds, consumer acceptance issues, a complicated regulatory framework, and more. So it's hard to know what will happen. And it's hard to know the best route to an aquaculture industry that doesn't empty the oceans. Market incentives are probably not strong enough, given the bizarre economics and distorted markets in the fishing industry. We may need a collection of national and international regulations to speed the adoption of alternatives. It's unclear whether these regulations should focus on the aquaculture industry, perhaps by limiting how much fish meal and fish oil they can use, or by regulating the fishing industry — setting and enforcing strict limits on catches.
Eaters also have a role in this, as do fish sellers at all levels: restaurant, retail, wholesale. We need to educate ourselves, ask tough questions and seek out more sustainable options. As with meat and dairy, it's not just about what we eat, but about what we eat eats, too.
Credits: Photoillustration is a composite by Ethicurean of jumping salmon from the Flickr collections of Gam_photodufffer's and from ; distillers grains photo from USDA's Rural Cooperatives magazine; grasshopper photo from tazintosh's Flickr collection. All Flickr photos are subject to Creative Commons Licenses.