Why sustainable aquaculture may be elusive?

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By Stephen G. Newman Ph.D. * President and CEO, AquaInTech Inc.

The second decade of the 21st century has been challenging for most of us. A rapidly mutating RNA virus (SARS-CoV-2) has been wreaking havoc on the global economy. Supply chains are damaged, and getting many things done in a timely manner is, at best, challenging. Attempts to keep the virus out via exclusion cannot work in the long term, and we are seeing repeated waves of variants that make immunization and wearing face masks crucial aspects of control. What is occurring is unprecedented in recent history.

With almost eight billion people, rapid movement between any two parts of the globe, and inadequate public health systems, we are likely many years away from the situation stabilizing despite pundits telling us otherwise. We are also continuing to see the impact of policies that deny that humans can impact their environment in any long-term negative way.

Rapid changes in localized ecosystems are occurring, and it looks as if humanity is just beginning to experience what could be a wild roller coaster ride.

There are few who will not agree that the need to be able to move forward without eroding the ability of the environment to support ongoing and future human activities is critical. The evidence is strong that we are failing at this in many ways.

“Atmospheric carbon dioxide levels are at concentrations that have not been seen for a very long time, not anytime in human history.”

Much of this is directly linked to human activities. We face an uncertain future as a species unless we figure out what we need to do and cooperatively work towards this common goal. We could very well be setting the planet on a course that will make it very difficult for humanity to continue to progress, i.e., the stage is being set for a grand failure of sustainability on a planet-wide scale.

Feeding 8 billion-plus people is no trivial matter. I firmly believe that aquaculture, when practiced sustainably, is an important part of the solution.

There are many reasons why I think this, although the bottom line is that seafood, in general, can be produced with much less of an environmental impact and at a lower monetary cost than most terrestrial sources of animal protein.

The challenge is to ensure that it is being done in a truly sustainable manner.

“The term “sustainable,” much as with other terms like green, eco, etc., has been widely twisted to suit marketing goals and unfortunately has lost any real meaning”.

The meaning of sustainability in aquaculture

What does sustainability mean for the aquaculturists, and is this even achievable? The Brundtland Commission, in its final report, Our Common Future, defined sustainability in simple terms:

It is not all that difficult to devote some percentage of a farm’s surface area to the collection, sedimentation, and treatment via aeration and bioremediation. There is a cost for this, but without it, sustainable production is not possible.

“Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.”

For aquaculture, this can be taken to mean that the production paradigms do not adversely impact the ability of subsequent generations to utilize a similar or evolved paradigm. Some of the issues that we face are:

  • 1. Cultural practices that negatively impact profitability and productivity have become SOPs.
  • 2. The impact of the production paradigm on the stability of the ecosystem that it is taking place in is rarely such that the result is a net-zero or a positive impact. The best example of this would be water being discharged is routinely heavily polluted with waste.
  • 3. Each step of the process has its constraints and should be considered on its own. These are linked, and fixing one does not mean that all are being addressed.
  • 4. Reducing the failure rate is essential for sustained profitability.

It is not possible in a short magazine article to cover even a small portion of this, so I am going to focus on shrimp farming as a working example. Land-based fish farming also has similar problems.

Applied sustainability in shrimp farming

Cage culture faces different constraints, although some such as fouling of net pens, the movement of pathogens from the wild into the captive animals, and the huge amounts of waste that are added to the immediate environment are obvious. SARGO had an innovative solution for this decades ago, but it was “cheaper’ to continue operating using the timehonored approaches.

From my perspective, the failure to deal with the underlying causes of the spread of disease is one of the major impediments to sustainability.”

In the Americas, the typical system entails the use of largely dirt ponds with inlet and outlet gates and low levels of stocking, typically under 30 per m2. This is slowly increasing as innovative technologies allow.

In SE Asia, the typical system involves much smaller ponds, often partially or wholly lined with plastic, with sumps in the middle of the ponds to collect the effluent and stocking at much higher densities, often many hundreds per m2. No one paradigm is universally used or consistently profitable, and while many claim sustainability, are they?

Discharging huge amounts of organic matter is not sustainable. Yet, in many parts of the world, this is the accepted practice.

“Water is heavily contaminated with organics from feed and feces and chemicals used to mitigate poor culture practices.”

Since the farms are on top of each other and there is no effective treatment before of the effluent after discharge, the water ends up being used by the adjacent farms. We are seeing a dramatic increase in localized algal blooms due to large amounts of organic matter entering formerly pristine ecosystems. Much of this is not from aquaculture (although it does contribute) as many agricultural practices don’t adequately treat effluents.

“Fisheries’ productivity is declining in areas that artisanal fishermen have relied on for millennia.”

Many think that because they do not see obvious problems, this means that there is not a problem. This may be true on a local level, but it still is not a sustainable practice.

Inadequate treatment of waste streams increases the risks of localized pollution with negative impacts on production.

It is not all that difficult to devote some percentage of a farm’s surface area to the collection, sedimentation, and treatment via aeration and bioremediation. There is a cost for this, but without it, sustainable production is not possible.

Polluting groundwater or overutilizing it is not a sustainable practice. Inland areas may use bore wells to fill the ponds and for daily water exchange.

This can deplete the water table. Deeper wells must be dug, and the result can be dry wells or water quality that is so poor that it cannot be used, and the farms must shut down. Limited water exchange by closing systems can offer some reprieve but without treating the resulting effluents is not a long-term solution.

Historically in some parts of the world, the best places for shrimp farms have been salt flats in mangrove swamps. In some areas cutting mangroves down to make way for farms is still a common practice.

Mangrove soils require extensive flushing before they are suitable for use for shrimp farming, although this is all too easily mitigated by lining the ponds and preventing any interaction between soils and the water.

“Mangroves are critical components of the global ecosystem, and much of the organic matter that is dumped, if it were discharged at reasonable levels, into these areas would foster growth.”

Mangroves should be cherished and allowed to thrive to stabilize soils and to lessen the impacts of the inevitable increases in sea level that human activity is bringing about. The aquatic animals that depend on the health of these ecosystems are a huge part of the food web.

Shrimp farming is approaching the 5 million MT a year level. The exact numbers are elusive, although most experts feel that this is a reasonable approximation.

Demand remains strong, and there is a great deal of economic pressure to continue to expand production. Even with production paradigms that are not sustainable global production could easily double in the coming decades.

Shrimp aquaculture consists of three or four distinct stages: broodstock production, production of larval and post-larval shrimp, nursery ponds that bridge this to the farm, and finally on the farm production.

These overlap, and even if exclusionary practices are successful in one component, it does not mean that all the other steps will also be free of the influence of pathogens.

Allowing large numbers of pathogens to enter production systems is not conducive to sustainability. Keeping pathogens out of production systems is challenging. However, it can be done.

Disease is a serious problem that consistently impacts shrimp farmers globally. Companies that claim to offer solutions without considering the nature by which pathogens enter production systems abound. One-step solutions to complex problems are rarely sustainable fixes.

Analysis of sustainability in shrimp farming

From my perspective, the failure to deal with the underlying causes of the spread of disease is one of the major impediments to sustainability. Each step in the process should be analyzed for each operation, and all sources of potential pathogen entry addressed. It is important to make a distinction between opportunistic and obligate pathogens.

There are many “experts” who will tell you that you need to control both. I believe that this is a fool’s errand. Control of obligate pathogens is via exclusion, although of course, it is not 100%. The movement of pathogens between the wild and the farmed environment is always going to be an element of production in systems that are open to the environment.

Control of opportunistic pathogens should be via exclusion where this is feasible and through the control of those factors that contribute to susceptibility. Some advocate that the environment be free of vibrios.

Broodstock are a major source of pathogens. Specific pathogenfree (SPF) does not mean all pathogen-free. Screening animals on a population basis is not sufficient for ensuring that pathogens cannot enter the production system via carriers.”

Frequently most are focused on those that cannot break down sucrose. This has no correlation with pathogenicity. Furthermore, microbiomes are complex, and when one creates a niche by eliminating or diminishing the presence of one species, it opens the niche for others.

Focusing on vibrios makes little sense without considering this. Many other species contain obligate and opportunistic pathogens that will adversely impact production if given the opening.

Reduction of stress is a critical element of production. Maintaining an environment that is consistent with this is not always a simple matter, and there are some that advocate that this is not needed.

Let animals die. After all, we want the strongest animals, and those will be the survivors. This might seem logical, but it is not consistent with sustainability and allows one to rationalize that the failure to address the underlying causes of these losses is acceptable.

Yields should be maximized to reduce the overall costs of production and improve profitability. Susceptibility to stress can be addressed via genetic programs that domesticate animals and by understanding the importance of well-aerated, clean production systems and high-quality, nutritious feeds.

Broodstock are a major source of pathogens. Specific pathogen-free (SPF) does not mean all pathogenfree. Screening animals on a population basis is not sufficient for ensuring that pathogens cannot enter the production system via carriers.

“Tolerance to the presence of most obligate pathogens should be as close to zero as one can realistically achieve.”

Typically, anything beyond 2% is not statistically achievable using current common approaches. This can and often is still too high. Failing to consider a given pathogens’ nature and ignoring what might be needed in an animal to force the pathogen to reveal itself also is an issue. It is simple to appear to be free of WSSV if the testing is done at temperatures where the virus cannot grow.

Failure to closely follow the histories of stocked animals to verify the effectiveness of screening protocols is as important, if not more so, than the screening itself. When there are disease outbreaks, the pathogens more than likely originated in carriers. It is well documented that pathogens can be missed in routine screening protocols.

Furthermore, there are many as of yet uncharacterized pathogens. Following OIE guidelines is not going to afford the level of cleanliness that is necessary for one to consider that this first and crucial step in the process is not resulting in problems downstream. Be open to looking for any and all obligate pathogens as they are discovered.

“If you have truly pathogen-free broodstock (not solely based on OIE criteria), the moment they leave a biosecure facility, one must consider that they may no longer be clean. It is routine practice in many areas to mix broodstock selected from ponds with “clean” animals.”

The hatchery then becomes a focal point for the proliferation of these pathogens. This is a high-density production environment where the potential for movement of pathogens between animals can be great.

Failure to understand this is a cause of many problems on the farm and a major source of disease issues. Live feeds must not be contaminated with obligate pathogens, and in stressful environments, one is much better off limiting the load of as many potential obligate pathogens as possible.

Algal and artemia production are sources of many bacterial and fungal pathogens. Most of these are opportunistic. They are easily controlled.

“There are many farmers who think that high survivals in the hatchery do not equate with high survivals on the farm.”

The opposite is the reality—high survivals in the hatchery and the nursery bode well for higher productivity on the farm. Income depends on growth, survival rates, and feed conversion ratios. Slow growth and low survival rates often result in high feed costs as a result of poor feed conversions, and consistent profitability becomes elusive.

Shrimp farming is not sustainable if the only time that farmers can make a profit is when competitors have problems. This, for the most part, is the state of the industry in 2021. Countries with high productivity often have serious disease problems which significantly impact the overall production.

Other countries can fill this void because they have not had the same problem. The balance shifts until the pathogens have moved into new areas or new pathogens arise.

“Sustainable shrimp farming will remain elusive until there are some fundamental changes in how shrimp are farmed.”

The economic incentives would be there if long-term profitability was the primary concern instead of the current “take what we can while we can get it” approach.

The cyclical shifts from country to country will continue until there is a global recognition that shrimp are a prized food item and production methods become more favorable towards less costly production. Sustainable production will ensure that the industry achieves this.

Stephen G. Newman has a bachelor’s degree from the University of Maryland in Conservation and Resource Management (ecology) and a Ph.D. from the University of Miami, in Marine Microbiology. He has over 40 years of experience working within a range of topics and approaches on aquaculture such as water quality, animal health, biosecurity with special focus on shrimp and salmonids. He founded Aquaintech in 1996 and continues to be CEO of this company to the present day. It is heavily focused on providing consulting services around the world on microbial technologies and biosecurity issues. sgnewm@aqua-in-tech.com www.aqua-in-tech.com www.bioremediationaquaculture.com www.sustainablegreenaquaculture.com

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