Agriculture isn’t natural. Anywhere agriculture is practiced, natural systems are altered and replaced by something new that differs, quantitatively or qualitatively, from earlier wildness. Because all agriculture affects the environment, the measure of proper stewardship isn’t whether agriculture affects the environment. Rather it is what the farmer chooses to do about those effects.
How should we view aquaculture and just what constitutes aquacultural sustainability? The word has become so hackneyed that SUVs are now given sustainability awards (yeah, that was my reaction too). Let me offer an operational definition to use here. Environmental sustainability means practicing in ways now that don’t preclude the opportunity for others to practice in the future.
This leads to the notion that: It’s ok to use environmental resources but it’s not ok to use them up. From a practical standpoint we probably don’t have the omniscience to know what is truly sustainable. It may be best to view sustainability as a journey rather than an endpoint.
With that in mind, where does aquaculture sit on its sustainability journey? While there isn’t universal agreement on what practices need to be addressed and in what order, perhaps some of the most important considerations are: what fish are fed, the local environmental effects of farms and health of the fish raised on those farms.
Many farm raised fish are carnivorous. Fish such as salmon, trout, sea bass (branzino), Kampachi are all meat eaters; shellfish such as shrimp are omnivorous. In the 1970s and 1980s farmed fish were fed diets high in fish oil and fish meal rendered from captured wild fish such as sardines and anchovies. From a nutritional point of view this was completely reasonable.
However, in some species, it took as much as 5 kg of wild caught fish to make the diet for 1 kg of farmed fish (a fish in/fish out ratio of 5:1). Furthermore, the capture of wild fish for rendering cannot expand as these fisheries are harvested at their utmost limits. As aquaculture grows the demand for fish oil and meal in fish diets has increased while their supply has not. Thus the reliance on rendered wild fish isn’t sustainable from either an environmental or business perspective.
To address the fish meal problem many, including the USDA, are looking to fill aquaculture’s protein needs with vegetable proteins as substitutes for fish meal. For instance Kampachi Farms is testing diets without fish meal for the Kampachi (Seriola rivoliana) they raise. In salmon, many of the better producers regularly achieve fish in/fish out ratios for fish meal of less than 1:1 meaning they are net producers of fish protein.
For fish meal replacements, it seems like the glass far more than half full.
In contrast, a larger problem looms with fish oil. Fish oil is included in aquaculture diets for the essential omega 3 fatty acids they contain. In the ocean, the essential omega 3 oils EPA and DHA are made in phytoplankton and move their way up the food chain. There is, however, no terrestrial counterpart to this. With very few exceptions (rattlesnakes being one), our source for essential omega 3 oils comes from the ocean. With anchovies and other rendered fish harvested at their limits, we have neither the ability to expand our omega 3 supply meaningfully nor are we able to reduce pressure on wild fisheries by substituting land based ingredients in the same way that vegetable protein substitutes for fish meal.
While there is no bright light of hope for fish oil, perhaps there is a glimmer. Alltech from Nicholasville, Kentucky ferments algae as a source of omega 3 for fish diets. These algae, derived from plankton, were adapted to grow in large fermentation vats. They contain the essential omega 3 fatty acid DHA and their incorporation into fish diets substitutes well for fish oil that would otherwise provide required omega 3s. A second example is the salmon company Verlasso, a partnership between DuPont and AquaChile, that feeds salmon a yeast grown in a DuPont fermentation process that produces EPA. Verlasso’s contribution has been to reduce the fish in/fish out ratio for fish oil from a worldwide average of 3:1 down to about 1:1.
With either the inclusion of Alltech algae or Verlasso yeast into a fish’s diet the outcome is to reduce the amount of fish oil consumed through aquaculture. This is good as far as it goes, but approaches like these need to be expanded dramatically if we are to see anything similar to the notable reduction in aquaculture’s fish meal consumption that vegetable proteins have provided.
The approaches identified are good but because of the low implementation, the glass is almost empty.
The Environment Around Farms
Aquaculture contributes to dissolved nutrient loads (hence affecting water quality) around farms through both fish excrement and uneaten fish food. To achieve sustainable farming, release of nutrients such as nitrogen and phosphorus must be maintained at levels that do not harm marine environments. Though nutrient release per se is not harmful it is important to measure their levels, the effects they have on surrounding systems and the duration of those effects.
In a large meta-study Carol Price and her colleagues undertook to do exactly that; her findings are a bit of a mixed bag. A paper in 2008 found that for Atlantic salmon 44 kg of nitrogen were released into the environment per ton of fish produced and that decreased to 11 kg/ton of salmon in a 2014 study.
A very interesting technical innovation important to reducing nutrient release by salmon farms is to place cameras at the depth of a few meters in the salmon’s pen. Operators can then view real time images during feeding sessions. At the moment any uneaten feed begins to fall below the fish, feeding is stopped. Before the advent of cameras it took about 2 kg of feed over the lifetime of a fish to raise 1 kg of salmon. With the implementation of cameras feed requirements have decreased to about 1.25 kg for the kg of salmon grown.
The Monterey Bay Aquarium’s Seafood Watch scientists find that nutrient discharge “. . . . can be considered somewhat insignificant compared to the natural transport of nutrients in the coastal currents. . .”. In the same study nutrients were measured nearby and the finding was that levels were elevated as far away as 30 meters from the farm but, importantly, not beyond that.
Decreasing nutrient releases and learning their presence is local is encouraging. However, the understanding about whether discharges are associated meaningful effects is lagging. We don’t really know what good performance looks like; that is to say we don’t know which levels matter and which don’t.
Completeness and transparency of information influences how we view environmental effects of aquaculture. Data available in the Americas, EU and Scandinavian countries are rich while those from Asia are skimpier. For the former group, there seems to be documented continual improvement. The glass is well more than half full.
Fish Health & Diseases
Picture a long equation. On the right side you have a single result that includes many different inputs collected from the left side. This is a (perhaps tortured) analogy to animal health. On the left side of the equation you have all the many different variables and inputs required to raise fish well. On the right side you have the health status of the fish.
Most animal health and welfare studies in aquaculture have been with salmon followed by shrimp. Both are challenged by bacterial and viral diseases. Let’s start with a look at what’s being done with salmon.
Salmon are susceptible to a number of bacterial diseases. Norway, the world’s largest salmon producer, introduced vaccination programs in earnest in the early 1990s. Success of the vaccines resulted in considerably less antibiotic usage on Norwegian farms and, since the early 90s, antibiotic use decreased by about 99%. In 2014, Norway used 511 kg of antibiotics to produce 1.34 million tonnes of salmon or 0.3 mg/kg of salmon (or 6 millionths of an ounce of antibiotics per pound of fish produced). Dr Paul Midtlyng, a former officer for fish health in the Norwegian Ministry of Agriculture puts that use in perspective by saying that 50,000 kg of antibiotics are used to treat humans in Norway whose aggregate weight is somewhere around 375,000 tonnes-a million tonnes less than the amount of salmon grown.
Similar performance has been achieved in the Faroe Islands and in New Zealand both of which raise salmon with, essentially, no antibiotics at all.
A different picture emerges in Chile where 563,200 kg of antibiotics were used to raise 895,000 tonnes of salmon in 2014. This is 1,650 times the usage rate as in Norway. Clearly bacterial diseases remain a problem in Chile that must be addressed.
The most pernicious viral disease in salmon is Infectious Salmon Anemia (ISA). During the early 2000s in the Faroe Islands and 2008 in Chile, severe ISA outbreaks caused devastating loss of salmon. In both countries the outbreaks evoked significant regulatory changes that led to improved husbandry practices. The advent of ISA strain specific vaccines has been quite important in controlling the disease. Though ISA still occurs, when it does, the response is swift and extensive and the disease seems to be contained. Importantly, though, it is not eradicated.
Shrimp are also beset by both viral and bacterial diseases. A recent bacterial outbreak called EMS (Early Mortality Syndrome) is leading to farming improvements in an unexpected way. EMS, a bacterial disease, was first seen in southern China in 2010 and by 2013 it had spread throughout the world. Infection is cataclysmic and results in 100% mortality.
Paradoxically antibiotic treatments aren’t helpful. This is because EMS disease incidence is reduced in ponds that have mature ecosystems characterized by a rich and varied bacterial population. Killing the resident bacteria with antibiotics makes a pond even more susceptible to EMS infection. The ongoing response is to improve all aspects of shrimp farming and it is this that will result in control or eradication of EMS.
Disease speaks. When disease occurs something, somewhere is wrong. If disease should occur, of course it must be treated. However, far more important is to understand its root causes. Unfortunately, understanding disease on a fish farm is much like epidemiological research for human diseases. Untangling what is cause and what is correlation is hugely difficult. It is worth the effort though. The only path to sustainable aquaculture is to raise animals in a way that prevents disease.
So we come full circle to the original question: Where does aquaculture sit on its sustainability journey?
The changes in aquaculture over the past 25 years are enormous. Aquaculture is the most scrutinized than anything else in our agricultural system. That scrutiny has resulted in enormous improvement and practices are much better now than they were in the 1980s. Success in replacing fish meal is excellent. We have a body of knowledge for how to reduce the use of fish oil but successful implementations are few and small. The view on disease is moving from treatment to prevention. All these are so positive.
Elsewhere, however, we must learn our way into an evermore sustainable future. Applying what we already know is important. Equally important is that we need knowledge we don’t yet have. Commitment not to sit on the status quo is needed in all areas of aquaculture.
I’m back to sizing up my glasses. In keeping with the thought that continuous improvement along the path to sustainability is what is paramount, how about this for our glass. The tap is running and the glass is filling. We need to leave the tap on.
Next up-many organizations have gathered standards for what it means to raise fish sustainably. I will briefly review some of the major initiatives and what they are doing to help the development of ever more sustainable aquaculture.
 A disclosure-I have no current relationship with Verlasso. Previously, I was a Verlasso co-founder.
Copyright © Scott Nichols, 2016