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Why Sustainable Aquaculture May Be Elusive?

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.


What does sustainability mean for the aquaculturist and is this even achievable? The Brundtland Commission in its final report, Our Common Future, defined sustainability in simple terms: "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. However, when we examine the current practices further and their impact on productivity, profitability, and the environment, sustainability is a goal not yet attained.


Sustainable shrimp farming will remain elusive until there are some fundamental changes in how shrimp are farmed. Let's look at some of the problems we face in current practices and what changes are needed for a sustainable future.


Shrimp harvest in Indonesia



SOME OF THE ISSUES WE FACE:

  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.

I am going to focus on shrimp farming as a working example. Land based fish farming also has similar problems. 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 time honored approaches.


There are many different production paradigms. Note that I have simplified things for the sake of this discussion. 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?


Heavily polluted pond effluent



WATER POLLUTION

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 are not seeing 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 farms 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 ground water 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.


Hainan Tilapia Pond



DESTRUCTION OF THE GLOBAL ECOSYSTEM

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.



Dead shrimp outside of the exit gate with blackened discharge.



PATHOGENS IN PRODUCTION SYSTEMS

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. 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%.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. Frequently most are focused on those that cannot breakdown 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 pathogen free. 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.


If you have truly pathogen free broodstock (not solely based on OIE criteria), the moment they leave a bio secure 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 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 is 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 in 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.


CONCLUSION

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 some fundamental changes in how shrimp are farmed. The economic incentives are 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.




This article will soon be published in Aquaculture Magazine. This is an edited version. Please look for the full article in Aquaculture Magazine or on their website https://aquaculturemag.com/.


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